Error if naked return when result variables are shadowed.

[pf3gnuchains/gcc-fork.git] / gcc / go / gofrontend / parse.cc

// parse.cc -- Go frontend parser.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "go-system.h"

#include "lex.h"
#include "gogo.h"
#include "types.h"
#include "statements.h"
#include "expressions.h"
#include "parse.h"

// Struct Parse::Enclosing_var_comparison.

// Return true if v1 should be considered to be less than v2.

bool
Parse::Enclosing_var_comparison::operator()(const Enclosing_var& v1,
                                            const Enclosing_var& v2)
{
  if (v1.var() == v2.var())
    return false;

  const std::string& n1(v1.var()->name());
  const std::string& n2(v2.var()->name());
  int i = n1.compare(n2);
  if (i < 0)
    return true;
  else if (i > 0)
    return false;

  // If we get here it means that a single nested function refers to
  // two different variables defined in enclosing functions, and both
  // variables have the same name.  I think this is impossible.
  go_unreachable();
}

// Class Parse.

Parse::Parse(Lex* lex, Gogo* gogo)
  : lex_(lex),
    token_(Token::make_invalid_token(0)),
    unget_token_(Token::make_invalid_token(0)),
    unget_token_valid_(false),
    gogo_(gogo),
    break_stack_(NULL),
    continue_stack_(NULL),
    iota_(0),
    enclosing_vars_()
{
}

// Return the current token.

const Token*
Parse::peek_token()
{
  if (this->unget_token_valid_)
    return &this->unget_token_;
  if (this->token_.is_invalid())
    this->token_ = this->lex_->next_token();
  return &this->token_;
}

// Advance to the next token and return it.

const Token*
Parse::advance_token()
{
  if (this->unget_token_valid_)
    {
      this->unget_token_valid_ = false;
      if (!this->token_.is_invalid())
        return &this->token_;
    }
  this->token_ = this->lex_->next_token();
  return &this->token_;
}

// Push a token back on the input stream.

void
Parse::unget_token(const Token& token)
{
  go_assert(!this->unget_token_valid_);
  this->unget_token_ = token;
  this->unget_token_valid_ = true;
}

// The location of the current token.

source_location
Parse::location()
{
  return this->peek_token()->location();
}

// IdentifierList = identifier { "," identifier } .

void
Parse::identifier_list(Typed_identifier_list* til)
{
  const Token* token = this->peek_token();
  while (true)
    {
      if (!token->is_identifier())
        {
          error_at(this->location(), "expected identifier");
          return;
        }
      std::string name =
        this->gogo_->pack_hidden_name(token->identifier(),
                                      token->is_identifier_exported());
      til->push_back(Typed_identifier(name, NULL, token->location()));
      token = this->advance_token();
      if (!token->is_op(OPERATOR_COMMA))
        return;
      token = this->advance_token();
    }
}

// ExpressionList = Expression { "," Expression } .

// If MAY_BE_SINK is true, the expressions in the list may be "_".

Expression_list*
Parse::expression_list(Expression* first, bool may_be_sink)
{
  Expression_list* ret = new Expression_list();
  if (first != NULL)
    ret->push_back(first);
  while (true)
    {
      ret->push_back(this->expression(PRECEDENCE_NORMAL, may_be_sink, true,
                                      NULL));

      const Token* token = this->peek_token();
      if (!token->is_op(OPERATOR_COMMA))
        return ret;

      // Most expression lists permit a trailing comma.
      source_location location = token->location();
      this->advance_token();
      if (!this->expression_may_start_here())
        {
          this->unget_token(Token::make_operator_token(OPERATOR_COMMA,
                                                       location));
          return ret;
        }
    }
}

// QualifiedIdent = [ PackageName "." ] identifier .
// PackageName = identifier .

// This sets *PNAME to the identifier and sets *PPACKAGE to the
// package or NULL if there isn't one.  This returns true on success,
// false on failure in which case it will have emitted an error
// message.

bool
Parse::qualified_ident(std::string* pname, Named_object** ppackage)
{
  const Token* token = this->peek_token();
  if (!token->is_identifier())
    {
      error_at(this->location(), "expected identifier");
      return false;
    }

  std::string name = token->identifier();
  bool is_exported = token->is_identifier_exported();
  name = this->gogo_->pack_hidden_name(name, is_exported);

  token = this->advance_token();
  if (!token->is_op(OPERATOR_DOT))
    {
      *pname = name;
      *ppackage = NULL;
      return true;
    }

  Named_object* package = this->gogo_->lookup(name, NULL);
  if (package == NULL || !package->is_package())
    {
      error_at(this->location(), "expected package");
      // We expect . IDENTIFIER; skip both.
      if (this->advance_token()->is_identifier())
        this->advance_token();
      return false;
    }

  package->package_value()->set_used();

  token = this->advance_token();
  if (!token->is_identifier())
    {
      error_at(this->location(), "expected identifier");
      return false;
    }

  name = token->identifier();

  if (name == "_")
    {
      error_at(this->location(), "invalid use of %<_%>");
      name = "blank";
    }

  if (package->name() == this->gogo_->package_name())
    name = this->gogo_->pack_hidden_name(name,
                                         token->is_identifier_exported());

  *pname = name;
  *ppackage = package;

  this->advance_token();

  return true;
}

// Type = TypeName | TypeLit | "(" Type ")" .
// TypeLit =
//      ArrayType | StructType | PointerType | FunctionType | InterfaceType |
//      SliceType | MapType | ChannelType .

Type*
Parse::type()
{
  const Token* token = this->peek_token();
  if (token->is_identifier())
    return this->type_name(true);
  else if (token->is_op(OPERATOR_LSQUARE))
    return this->array_type(false);
  else if (token->is_keyword(KEYWORD_CHAN)
           || token->is_op(OPERATOR_CHANOP))
    return this->channel_type();
  else if (token->is_keyword(KEYWORD_INTERFACE))
    return this->interface_type();
  else if (token->is_keyword(KEYWORD_FUNC))
    {
      source_location location = token->location();
      this->advance_token();
      Type* type = this->signature(NULL, location);
      if (type == NULL)
        return Type::make_error_type();
      return type;
    }
  else if (token->is_keyword(KEYWORD_MAP))
    return this->map_type();
  else if (token->is_keyword(KEYWORD_STRUCT))
    return this->struct_type();
  else if (token->is_op(OPERATOR_MULT))
    return this->pointer_type();
  else if (token->is_op(OPERATOR_LPAREN))
    {
      this->advance_token();
      Type* ret = this->type();
      if (this->peek_token()->is_op(OPERATOR_RPAREN))
        this->advance_token();
      else
        {
          if (!ret->is_error_type())
            error_at(this->location(), "expected %<)%>");
        }
      return ret;
    }
  else
    {
      error_at(token->location(), "expected type");
      return Type::make_error_type();
    }
}

bool
Parse::type_may_start_here()
{
  const Token* token = this->peek_token();
  return (token->is_identifier()
          || token->is_op(OPERATOR_LSQUARE)
          || token->is_op(OPERATOR_CHANOP)
          || token->is_keyword(KEYWORD_CHAN)
          || token->is_keyword(KEYWORD_INTERFACE)
          || token->is_keyword(KEYWORD_FUNC)
          || token->is_keyword(KEYWORD_MAP)
          || token->is_keyword(KEYWORD_STRUCT)
          || token->is_op(OPERATOR_MULT)
          || token->is_op(OPERATOR_LPAREN));
}

// TypeName = QualifiedIdent .

// If MAY_BE_NIL is true, then an identifier with the value of the
// predefined constant nil is accepted, returning the nil type.

Type*
Parse::type_name(bool issue_error)
{
  source_location location = this->location();

  std::string name;
  Named_object* package;
  if (!this->qualified_ident(&name, &package))
    return Type::make_error_type();

  Named_object* named_object;
  if (package == NULL)
    named_object = this->gogo_->lookup(name, NULL);
  else
    {
      named_object = package->package_value()->lookup(name);
      if (named_object == NULL
          && issue_error
          && package->name() != this->gogo_->package_name())
        {
          // Check whether the name is there but hidden.
          std::string s = ('.' + package->package_value()->unique_prefix()
                           + '.' + package->package_value()->name()
                           + '.' + name);
          named_object = package->package_value()->lookup(s);
          if (named_object != NULL)
            {
              const std::string& packname(package->package_value()->name());
              error_at(location, "invalid reference to hidden type %<%s.%s%>",
                       Gogo::message_name(packname).c_str(),
                       Gogo::message_name(name).c_str());
              issue_error = false;
            }
        }
    }

  bool ok = true;
  if (named_object == NULL)
    {
      if (package == NULL)
        named_object = this->gogo_->add_unknown_name(name, location);
      else
        {
          const std::string& packname(package->package_value()->name());
          error_at(location, "reference to undefined identifier %<%s.%s%>",
                   Gogo::message_name(packname).c_str(),
                   Gogo::message_name(name).c_str());
          issue_error = false;
          ok = false;
        }
    }
  else if (named_object->is_type())
    {
      if (!named_object->type_value()->is_visible())
        ok = false;
    }
  else if (named_object->is_unknown() || named_object->is_type_declaration())
    ;
  else
    ok = false;

  if (!ok)
    {
      if (issue_error)
        error_at(location, "expected type");
      return Type::make_error_type();
    }

  if (named_object->is_type())
    return named_object->type_value();
  else if (named_object->is_unknown() || named_object->is_type_declaration())
    return Type::make_forward_declaration(named_object);
  else
    go_unreachable();
}

// ArrayType = "[" [ ArrayLength ] "]" ElementType .
// ArrayLength = Expression .
// ElementType = CompleteType .

Type*
Parse::array_type(bool may_use_ellipsis)
{
  go_assert(this->peek_token()->is_op(OPERATOR_LSQUARE));
  const Token* token = this->advance_token();

  Expression* length = NULL;
  if (token->is_op(OPERATOR_RSQUARE))
    this->advance_token();
  else
    {
      if (!token->is_op(OPERATOR_ELLIPSIS))
        length = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
      else if (may_use_ellipsis)
        {
          // An ellipsis is used in composite literals to represent a
          // fixed array of the size of the number of elements.  We
          // use a length of nil to represent this, and change the
          // length when parsing the composite literal.
          length = Expression::make_nil(this->location());
          this->advance_token();
        }
      else
        {
          error_at(this->location(),
                   "use of %<[...]%> outside of array literal");
          length = Expression::make_error(this->location());
          this->advance_token();
        }
      if (!this->peek_token()->is_op(OPERATOR_RSQUARE))
        {
          error_at(this->location(), "expected %<]%>");
          return Type::make_error_type();
        }
      this->advance_token();
    }

  Type* element_type = this->type();

  return Type::make_array_type(element_type, length);
}

// MapType = "map" "[" KeyType "]" ValueType .
// KeyType = CompleteType .
// ValueType = CompleteType .

Type*
Parse::map_type()
{
  source_location location = this->location();
  go_assert(this->peek_token()->is_keyword(KEYWORD_MAP));
  if (!this->advance_token()->is_op(OPERATOR_LSQUARE))
    {
      error_at(this->location(), "expected %<[%>");
      return Type::make_error_type();
    }
  this->advance_token();

  Type* key_type = this->type();

  if (!this->peek_token()->is_op(OPERATOR_RSQUARE))
    {
      error_at(this->location(), "expected %<]%>");
      return Type::make_error_type();
    }
  this->advance_token();

  Type* value_type = this->type();

  if (key_type->is_error_type() || value_type->is_error_type())
    return Type::make_error_type();

  return Type::make_map_type(key_type, value_type, location);
}

// StructType     = "struct" "{" { FieldDecl ";" } "}" .

Type*
Parse::struct_type()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_STRUCT));
  source_location location = this->location();
  if (!this->advance_token()->is_op(OPERATOR_LCURLY))
    {
      source_location token_loc = this->location();
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON)
          && this->advance_token()->is_op(OPERATOR_LCURLY))
        error_at(token_loc, "unexpected semicolon or newline before %<{%>");
      else
        {
          error_at(this->location(), "expected %<{%>");
          return Type::make_error_type();
        }
    }
  this->advance_token();

  Struct_field_list* sfl = new Struct_field_list;
  while (!this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      this->field_decl(sfl);
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
        this->advance_token();
      else if (!this->peek_token()->is_op(OPERATOR_RCURLY))
        {
          error_at(this->location(), "expected %<;%> or %<}%> or newline");
          if (!this->skip_past_error(OPERATOR_RCURLY))
            return Type::make_error_type();
        }
    }
  this->advance_token();

  for (Struct_field_list::const_iterator pi = sfl->begin();
       pi != sfl->end();
       ++pi)
    {
      if (pi->type()->is_error_type())
        return pi->type();
      for (Struct_field_list::const_iterator pj = pi + 1;
           pj != sfl->end();
           ++pj)
        {
          if (pi->field_name() == pj->field_name()
              && !Gogo::is_sink_name(pi->field_name()))
            error_at(pi->location(), "duplicate field name %<%s%>",
                     Gogo::message_name(pi->field_name()).c_str());
        }
    }

  return Type::make_struct_type(sfl, location);
}

// FieldDecl = (IdentifierList CompleteType | TypeName) [ Tag ] .
// Tag = string_lit .

void
Parse::field_decl(Struct_field_list* sfl)
{
  const Token* token = this->peek_token();
  source_location location = token->location();
  bool is_anonymous;
  bool is_anonymous_pointer;
  if (token->is_op(OPERATOR_MULT))
    {
      is_anonymous = true;
      is_anonymous_pointer = true;
    }
  else if (token->is_identifier())
    {
      std::string id = token->identifier();
      bool is_id_exported = token->is_identifier_exported();
      source_location id_location = token->location();
      token = this->advance_token();
      is_anonymous = (token->is_op(OPERATOR_SEMICOLON)
                      || token->is_op(OPERATOR_RCURLY)
                      || token->is_op(OPERATOR_DOT)
                      || token->is_string());
      is_anonymous_pointer = false;
      this->unget_token(Token::make_identifier_token(id, is_id_exported,
                                                     id_location));
    }
  else
    {
      error_at(this->location(), "expected field name");
      while (!token->is_op(OPERATOR_SEMICOLON)
             && !token->is_op(OPERATOR_RCURLY)
             && !token->is_eof())
        token = this->advance_token();
      return;
    }

  if (is_anonymous)
    {
      if (is_anonymous_pointer)
        {
          this->advance_token();
          if (!this->peek_token()->is_identifier())
            {
              error_at(this->location(), "expected field name");
              while (!token->is_op(OPERATOR_SEMICOLON)
                     && !token->is_op(OPERATOR_RCURLY)
                     && !token->is_eof())
                token = this->advance_token();
              return;
            }
        }
      Type* type = this->type_name(true);

      std::string tag;
      if (this->peek_token()->is_string())
        {
          tag = this->peek_token()->string_value();
          this->advance_token();
        }

      if (!type->is_error_type())
        {
          if (is_anonymous_pointer)
            type = Type::make_pointer_type(type);
          sfl->push_back(Struct_field(Typed_identifier("", type, location)));
          if (!tag.empty())
            sfl->back().set_tag(tag);
        }
    }
  else
    {
      Typed_identifier_list til;
      while (true)
        {
          token = this->peek_token();
          if (!token->is_identifier())
            {
              error_at(this->location(), "expected identifier");
              return;
            }
          std::string name =
            this->gogo_->pack_hidden_name(token->identifier(),
                                          token->is_identifier_exported());
          til.push_back(Typed_identifier(name, NULL, token->location()));
          if (!this->advance_token()->is_op(OPERATOR_COMMA))
            break;
          this->advance_token();
        }

      Type* type = this->type();

      std::string tag;
      if (this->peek_token()->is_string())
        {
          tag = this->peek_token()->string_value();
          this->advance_token();
        }

      for (Typed_identifier_list::iterator p = til.begin();
           p != til.end();
           ++p)
        {
          p->set_type(type);
          sfl->push_back(Struct_field(*p));
          if (!tag.empty())
            sfl->back().set_tag(tag);
        }
    }
}

// PointerType = "*" Type .

Type*
Parse::pointer_type()
{
  go_assert(this->peek_token()->is_op(OPERATOR_MULT));
  this->advance_token();
  Type* type = this->type();
  if (type->is_error_type())
    return type;
  return Type::make_pointer_type(type);
}

// ChannelType   = Channel | SendChannel | RecvChannel .
// Channel       = "chan" ElementType .
// SendChannel   = "chan" "<-" ElementType .
// RecvChannel   = "<-" "chan" ElementType .

Type*
Parse::channel_type()
{
  const Token* token = this->peek_token();
  bool send = true;
  bool receive = true;
  if (token->is_op(OPERATOR_CHANOP))
    {
      if (!this->advance_token()->is_keyword(KEYWORD_CHAN))
        {
          error_at(this->location(), "expected %<chan%>");
          return Type::make_error_type();
        }
      send = false;
      this->advance_token();
    }
  else
    {
      go_assert(token->is_keyword(KEYWORD_CHAN));
      if (this->advance_token()->is_op(OPERATOR_CHANOP))
        {
          receive = false;
          this->advance_token();
        }
    }

  // Better error messages for the common error of omitting the
  // channel element type.
  if (!this->type_may_start_here())
    {
      token = this->peek_token();
      if (token->is_op(OPERATOR_RCURLY))
        error_at(this->location(), "unexpected %<}%> in channel type");
      else if (token->is_op(OPERATOR_RPAREN))
        error_at(this->location(), "unexpected %<)%> in channel type");
      else if (token->is_op(OPERATOR_COMMA))
        error_at(this->location(), "unexpected comma in channel type");
      else
        error_at(this->location(), "expected channel element type");
      return Type::make_error_type();
    }

  Type* element_type = this->type();
  return Type::make_channel_type(send, receive, element_type);
}

// Give an error for a duplicate parameter or receiver name.

void
Parse::check_signature_names(const Typed_identifier_list* params,
                             Parse::Names* names)
{
  for (Typed_identifier_list::const_iterator p = params->begin();
       p != params->end();
       ++p)
    {
      if (p->name().empty() || Gogo::is_sink_name(p->name()))
        continue;
      std::pair<std::string, const Typed_identifier*> val =
        std::make_pair(p->name(), &*p);
      std::pair<Parse::Names::iterator, bool> ins = names->insert(val);
      if (!ins.second)
        {
          error_at(p->location(), "redefinition of %qs",
                   Gogo::message_name(p->name()).c_str());
          inform(ins.first->second->location(),
                 "previous definition of %qs was here",
                 Gogo::message_name(p->name()).c_str());
        }
    }
}

// Signature      = Parameters [ Result ] .

// RECEIVER is the receiver if there is one, or NULL.  LOCATION is the
// location of the start of the type.

// This returns NULL on a parse error.

Function_type*
Parse::signature(Typed_identifier* receiver, source_location location)
{
  bool is_varargs = false;
  Typed_identifier_list* params;
  bool params_ok = this->parameters(&params, &is_varargs);

  Typed_identifier_list* results = NULL;
  if (this->peek_token()->is_op(OPERATOR_LPAREN)
      || this->type_may_start_here())
    {
      if (!this->result(&results))
        return NULL;
    }

  if (!params_ok)
    return NULL;

  Parse::Names names;
  if (params != NULL)
    this->check_signature_names(params, &names);
  if (results != NULL)
    this->check_signature_names(results, &names);

  Function_type* ret = Type::make_function_type(receiver, params, results,
                                                location);
  if (is_varargs)
    ret->set_is_varargs();
  return ret;
}

// Parameters     = "(" [ ParameterList [ "," ] ] ")" .

// This returns false on a parse error.

bool
Parse::parameters(Typed_identifier_list** pparams, bool* is_varargs)
{
  *pparams = NULL;

  if (!this->peek_token()->is_op(OPERATOR_LPAREN))
    {
      error_at(this->location(), "expected %<(%>");
      return false;
    }

  Typed_identifier_list* params = NULL;
  bool saw_error = false;

  const Token* token = this->advance_token();
  if (!token->is_op(OPERATOR_RPAREN))
    {
      params = this->parameter_list(is_varargs);
      if (params == NULL)
        saw_error = true;
      token = this->peek_token();
    }

  // The optional trailing comma is picked up in parameter_list.

  if (!token->is_op(OPERATOR_RPAREN))
    error_at(this->location(), "expected %<)%>");
  else
    this->advance_token();

  if (saw_error)
    return false;

  *pparams = params;
  return true;
}

// ParameterList  = ParameterDecl { "," ParameterDecl } .

// This sets *IS_VARARGS if the list ends with an ellipsis.
// IS_VARARGS will be NULL if varargs are not permitted.

// We pick up an optional trailing comma.

// This returns NULL if some error is seen.

Typed_identifier_list*
Parse::parameter_list(bool* is_varargs)
{
  source_location location = this->location();
  Typed_identifier_list* ret = new Typed_identifier_list();

  bool saw_error = false;

  // If we see an identifier and then a comma, then we don't know
  // whether we are looking at a list of identifiers followed by a
  // type, or a list of types given by name.  We have to do an
  // arbitrary lookahead to figure it out.

  bool parameters_have_names;
  const Token* token = this->peek_token();
  if (!token->is_identifier())
    {
      // This must be a type which starts with something like '*'.
      parameters_have_names = false;
    }
  else
    {
      std::string name = token->identifier();
      bool is_exported = token->is_identifier_exported();
      source_location location = token->location();
      token = this->advance_token();
      if (!token->is_op(OPERATOR_COMMA))
        {
          if (token->is_op(OPERATOR_DOT))
            {
              // This is a qualified identifier, which must turn out
              // to be a type.
              parameters_have_names = false;
            }
          else if (token->is_op(OPERATOR_RPAREN))
            {
              // A single identifier followed by a parenthesis must be
              // a type name.
              parameters_have_names = false;
            }
          else
            {
              // An identifier followed by something other than a
              // comma or a dot or a right parenthesis must be a
              // parameter name followed by a type.
              parameters_have_names = true;
            }

          this->unget_token(Token::make_identifier_token(name, is_exported,
                                                         location));
        }
      else
        {
          // An identifier followed by a comma may be the first in a
          // list of parameter names followed by a type, or it may be
          // the first in a list of types without parameter names.  To
          // find out we gather as many identifiers separated by
          // commas as we can.
          std::string id_name = this->gogo_->pack_hidden_name(name,
                                                              is_exported);
          ret->push_back(Typed_identifier(id_name, NULL, location));
          bool just_saw_comma = true;
          while (this->advance_token()->is_identifier())
            {
              name = this->peek_token()->identifier();
              is_exported = this->peek_token()->is_identifier_exported();
              location = this->peek_token()->location();
              id_name = this->gogo_->pack_hidden_name(name, is_exported);
              ret->push_back(Typed_identifier(id_name, NULL, location));
              if (!this->advance_token()->is_op(OPERATOR_COMMA))
                {
                  just_saw_comma = false;
                  break;
                }
            }

          if (just_saw_comma)
            {
              // We saw ID1 "," ID2 "," followed by something which
              // was not an identifier.  We must be seeing the start
              // of a type, and ID1 and ID2 must be types, and the
              // parameters don't have names.
              parameters_have_names = false;
            }
          else if (this->peek_token()->is_op(OPERATOR_RPAREN))
            {
              // We saw ID1 "," ID2 ")".  ID1 and ID2 must be types,
              // and the parameters don't have names.
              parameters_have_names = false;
            }
          else if (this->peek_token()->is_op(OPERATOR_DOT))
            {
              // We saw ID1 "," ID2 ".".  ID2 must be a package name,
              // ID1 must be a type, and the parameters don't have
              // names.
              parameters_have_names = false;
              this->unget_token(Token::make_identifier_token(name, is_exported,
                                                             location));
              ret->pop_back();
              just_saw_comma = true;
            }
          else
            {
              // We saw ID1 "," ID2 followed by something other than
              // ",", ".", or ")".  We must be looking at the start of
              // a type, and ID1 and ID2 must be parameter names.
              parameters_have_names = true;
            }

          if (parameters_have_names)
            {
              go_assert(!just_saw_comma);
              // We have just seen ID1, ID2 xxx.
              Type* type;
              if (!this->peek_token()->is_op(OPERATOR_ELLIPSIS))
                type = this->type();
              else
                {
                  error_at(this->location(), "%<...%> only permits one name");
                  saw_error = true;
                  this->advance_token();
                  type = this->type();
                }
              for (size_t i = 0; i < ret->size(); ++i)
                ret->set_type(i, type);
              if (!this->peek_token()->is_op(OPERATOR_COMMA))
                return saw_error ? NULL : ret;
              if (this->advance_token()->is_op(OPERATOR_RPAREN))
                return saw_error ? NULL : ret;
            }
          else
            {
              Typed_identifier_list* tret = new Typed_identifier_list();
              for (Typed_identifier_list::const_iterator p = ret->begin();
                   p != ret->end();
                   ++p)
                {
                  Named_object* no = this->gogo_->lookup(p->name(), NULL);
                  Type* type;
                  if (no == NULL)
                    no = this->gogo_->add_unknown_name(p->name(),
                                                       p->location());

                  if (no->is_type())
                    type = no->type_value();
                  else if (no->is_unknown() || no->is_type_declaration())
                    type = Type::make_forward_declaration(no);
                  else
                    {
                      error_at(p->location(), "expected %<%s%> to be a type",
                               Gogo::message_name(p->name()).c_str());
                      saw_error = true;
                      type = Type::make_error_type();
                    }
                  tret->push_back(Typed_identifier("", type, p->location()));
                }
              delete ret;
              ret = tret;
              if (!just_saw_comma
                  || this->peek_token()->is_op(OPERATOR_RPAREN))
                return saw_error ? NULL : ret;
            }
        }
    }

  bool mix_error = false;
  this->parameter_decl(parameters_have_names, ret, is_varargs, &mix_error);
  while (this->peek_token()->is_op(OPERATOR_COMMA))
    {
      if (is_varargs != NULL && *is_varargs)
        {
          error_at(this->location(), "%<...%> must be last parameter");
          saw_error = true;
        }
      if (this->advance_token()->is_op(OPERATOR_RPAREN))
        break;
      this->parameter_decl(parameters_have_names, ret, is_varargs, &mix_error);
    }
  if (mix_error)
    {
      error_at(location, "invalid named/anonymous mix");
      saw_error = true;
    }
  if (saw_error)
    {
      delete ret;
      return NULL;
    }
  return ret;
}

// ParameterDecl  = [ IdentifierList ] [ "..." ] Type .

void
Parse::parameter_decl(bool parameters_have_names,
                      Typed_identifier_list* til,
                      bool* is_varargs,
                      bool* mix_error)
{
  if (!parameters_have_names)
    {
      Type* type;
      source_location location = this->location();
      if (!this->peek_token()->is_identifier())
        {
          if (!this->peek_token()->is_op(OPERATOR_ELLIPSIS))
            type = this->type();
          else
            {
              if (is_varargs == NULL)
                error_at(this->location(), "invalid use of %<...%>");
              else
                *is_varargs = true;
              this->advance_token();
              if (is_varargs == NULL
                  && this->peek_token()->is_op(OPERATOR_RPAREN))
                type = Type::make_error_type();
              else
                {
                  Type* element_type = this->type();
                  type = Type::make_array_type(element_type, NULL);
                }
            }
        }
      else
        {
          type = this->type_name(false);
          if (type->is_error_type()
              || (!this->peek_token()->is_op(OPERATOR_COMMA)
                  && !this->peek_token()->is_op(OPERATOR_RPAREN)))
            {
              *mix_error = true;
              while (!this->peek_token()->is_op(OPERATOR_COMMA)
                     && !this->peek_token()->is_op(OPERATOR_RPAREN))
                this->advance_token();
            }
        }
      if (!type->is_error_type())
        til->push_back(Typed_identifier("", type, location));
    }
  else
    {
      size_t orig_count = til->size();
      if (this->peek_token()->is_identifier())
        this->identifier_list(til);
      else
        *mix_error = true;
      size_t new_count = til->size();

      Type* type;
      if (!this->peek_token()->is_op(OPERATOR_ELLIPSIS))
        type = this->type();
      else
        {
          if (is_varargs == NULL)
            error_at(this->location(), "invalid use of %<...%>");
          else if (new_count > orig_count + 1)
            error_at(this->location(), "%<...%> only permits one name");
          else
            *is_varargs = true;
          this->advance_token();
          Type* element_type = this->type();
          type = Type::make_array_type(element_type, NULL);
        }
      for (size_t i = orig_count; i < new_count; ++i)
        til->set_type(i, type);
    }
}

// Result         = Parameters | Type .

// This returns false on a parse error.

bool
Parse::result(Typed_identifier_list** presults)
{
  if (this->peek_token()->is_op(OPERATOR_LPAREN))
    return this->parameters(presults, NULL);
  else
    {
      source_location location = this->location();
      Type* type = this->type();
      if (type->is_error_type())
        {
          *presults = NULL;
          return false;
        }
      Typed_identifier_list* til = new Typed_identifier_list();
      til->push_back(Typed_identifier("", type, location));
      *presults = til;
      return true;
    }
}

// Block = "{" [ StatementList ] "}" .

// Returns the location of the closing brace.

source_location
Parse::block()
{
  if (!this->peek_token()->is_op(OPERATOR_LCURLY))
    {
      source_location loc = this->location();
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON)
          && this->advance_token()->is_op(OPERATOR_LCURLY))
        error_at(loc, "unexpected semicolon or newline before %<{%>");
      else
        {
          error_at(this->location(), "expected %<{%>");
          return UNKNOWN_LOCATION;
        }
    }

  const Token* token = this->advance_token();

  if (!token->is_op(OPERATOR_RCURLY))
    {
      this->statement_list();
      token = this->peek_token();
      if (!token->is_op(OPERATOR_RCURLY))
        {
          if (!token->is_eof() || !saw_errors())
            error_at(this->location(), "expected %<}%>");

          // Skip ahead to the end of the block, in hopes of avoiding
          // lots of meaningless errors.
          source_location ret = token->location();
          int nest = 0;
          while (!token->is_eof())
            {
              if (token->is_op(OPERATOR_LCURLY))
                ++nest;
              else if (token->is_op(OPERATOR_RCURLY))
                {
                  --nest;
                  if (nest < 0)
                    {
                      this->advance_token();
                      break;
                    }
                }
              token = this->advance_token();
              ret = token->location();
            }
          return ret;
        }
    }

  source_location ret = token->location();
  this->advance_token();
  return ret;
}

// InterfaceType      = "interface" "{" [ MethodSpecList ] "}" .
// MethodSpecList     = MethodSpec { ";" MethodSpec } [ ";" ] .

Type*
Parse::interface_type()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_INTERFACE));
  source_location location = this->location();

  if (!this->advance_token()->is_op(OPERATOR_LCURLY))
    {
      source_location token_loc = this->location();
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON)
          && this->advance_token()->is_op(OPERATOR_LCURLY))
        error_at(token_loc, "unexpected semicolon or newline before %<{%>");
      else
        {
          error_at(this->location(), "expected %<{%>");
          return Type::make_error_type();
        }
    }
  this->advance_token();

  Typed_identifier_list* methods = new Typed_identifier_list();
  if (!this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      this->method_spec(methods);
      while (this->peek_token()->is_op(OPERATOR_SEMICOLON))
        {
          if (this->advance_token()->is_op(OPERATOR_RCURLY))
            break;
          this->method_spec(methods);
        }
      if (!this->peek_token()->is_op(OPERATOR_RCURLY))
        {
          error_at(this->location(), "expected %<}%>");
          while (!this->advance_token()->is_op(OPERATOR_RCURLY))
            {
              if (this->peek_token()->is_eof())
                return Type::make_error_type();
            }
        }
    }
  this->advance_token();

  if (methods->empty())
    {
      delete methods;
      methods = NULL;
    }

  Interface_type* ret = Type::make_interface_type(methods, location);
  this->gogo_->record_interface_type(ret);
  return ret;
}

// MethodSpec         = MethodName Signature | InterfaceTypeName .
// MethodName         = identifier .
// InterfaceTypeName  = TypeName .

void
Parse::method_spec(Typed_identifier_list* methods)
{
  const Token* token = this->peek_token();
  if (!token->is_identifier())
    {
      error_at(this->location(), "expected identifier");
      return;
    }

  std::string name = token->identifier();
  bool is_exported = token->is_identifier_exported();
  source_location location = token->location();

  if (this->advance_token()->is_op(OPERATOR_LPAREN))
    {
      // This is a MethodName.
      name = this->gogo_->pack_hidden_name(name, is_exported);
      Type* type = this->signature(NULL, location);
      if (type == NULL)
        return;
      methods->push_back(Typed_identifier(name, type, location));
    }
  else
    {
      this->unget_token(Token::make_identifier_token(name, is_exported,
                                                     location));
      Type* type = this->type_name(false);
      if (type->is_error_type()
          || (!this->peek_token()->is_op(OPERATOR_SEMICOLON)
              && !this->peek_token()->is_op(OPERATOR_RCURLY)))
        {
          if (this->peek_token()->is_op(OPERATOR_COMMA))
            error_at(this->location(),
                     "name list not allowed in interface type");
          else
            error_at(location, "expected signature or type name");
          token = this->peek_token();
          while (!token->is_eof()
                 && !token->is_op(OPERATOR_SEMICOLON)
                 && !token->is_op(OPERATOR_RCURLY))
            token = this->advance_token();
          return;
        }
      // This must be an interface type, but we can't check that now.
      // We check it and pull out the methods in
      // Interface_type::do_verify.
      methods->push_back(Typed_identifier("", type, location));
    }
}

// Declaration = ConstDecl | TypeDecl | VarDecl | FunctionDecl | MethodDecl .

void
Parse::declaration()
{
  const Token* token = this->peek_token();
  if (token->is_keyword(KEYWORD_CONST))
    this->const_decl();
  else if (token->is_keyword(KEYWORD_TYPE))
    this->type_decl();
  else if (token->is_keyword(KEYWORD_VAR))
    this->var_decl();
  else if (token->is_keyword(KEYWORD_FUNC))
    this->function_decl();
  else
    {
      error_at(this->location(), "expected declaration");
      this->advance_token();
    }
}

bool
Parse::declaration_may_start_here()
{
  const Token* token = this->peek_token();
  return (token->is_keyword(KEYWORD_CONST)
          || token->is_keyword(KEYWORD_TYPE)
          || token->is_keyword(KEYWORD_VAR)
          || token->is_keyword(KEYWORD_FUNC));
}

// Decl<P> = P | "(" [ List<P> ] ")" .

void
Parse::decl(void (Parse::*pfn)(void*), void* varg)
{
  if (this->peek_token()->is_eof())
    {
      if (!saw_errors())
        error_at(this->location(), "unexpected end of file");
      return;
    }

  if (!this->peek_token()->is_op(OPERATOR_LPAREN))
    (this->*pfn)(varg);
  else
    {
      if (!this->advance_token()->is_op(OPERATOR_RPAREN))
        {
          this->list(pfn, varg, true);
          if (!this->peek_token()->is_op(OPERATOR_RPAREN))
            {
              error_at(this->location(), "missing %<)%>");
              while (!this->advance_token()->is_op(OPERATOR_RPAREN))
                {
                  if (this->peek_token()->is_eof())
                    return;
                }
            }
        }
      this->advance_token();
    }
}

// List<P> = P { ";" P } [ ";" ] .

// In order to pick up the trailing semicolon we need to know what
// might follow.  This is either a '}' or a ')'.

void
Parse::list(void (Parse::*pfn)(void*), void* varg, bool follow_is_paren)
{
  (this->*pfn)(varg);
  Operator follow = follow_is_paren ? OPERATOR_RPAREN : OPERATOR_RCURLY;
  while (this->peek_token()->is_op(OPERATOR_SEMICOLON)
         || this->peek_token()->is_op(OPERATOR_COMMA))
    {
      if (this->peek_token()->is_op(OPERATOR_COMMA))
        error_at(this->location(), "unexpected comma");
      if (this->advance_token()->is_op(follow))
        break;
      (this->*pfn)(varg);
    }
}

// ConstDecl      = "const" ( ConstSpec | "(" { ConstSpec ";" } ")" ) .

void
Parse::const_decl()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_CONST));
  this->advance_token();
  this->reset_iota();

  Type* last_type = NULL;
  Expression_list* last_expr_list = NULL;

  if (!this->peek_token()->is_op(OPERATOR_LPAREN))
    this->const_spec(&last_type, &last_expr_list);
  else
    {
      this->advance_token();
      while (!this->peek_token()->is_op(OPERATOR_RPAREN))
        {
          this->const_spec(&last_type, &last_expr_list);
          if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
            this->advance_token();
          else if (!this->peek_token()->is_op(OPERATOR_RPAREN))
            {
              error_at(this->location(), "expected %<;%> or %<)%> or newline");
              if (!this->skip_past_error(OPERATOR_RPAREN))
                return;
            }
        }
      this->advance_token();
    }

  if (last_expr_list != NULL)
    delete last_expr_list;
}

// ConstSpec = IdentifierList [ [ CompleteType ] "=" ExpressionList ] .

void
Parse::const_spec(Type** last_type, Expression_list** last_expr_list)
{
  Typed_identifier_list til;
  this->identifier_list(&til);

  Type* type = NULL;
  if (this->type_may_start_here())
    {
      type = this->type();
      *last_type = NULL;
      *last_expr_list = NULL;
    }

  Expression_list *expr_list;
  if (!this->peek_token()->is_op(OPERATOR_EQ))
    {
      if (*last_expr_list == NULL)
        {
          error_at(this->location(), "expected %<=%>");
          return;
        }
      type = *last_type;
      expr_list = new Expression_list;
      for (Expression_list::const_iterator p = (*last_expr_list)->begin();
           p != (*last_expr_list)->end();
           ++p)
        expr_list->push_back((*p)->copy());
    }
  else
    {
      this->advance_token();
      expr_list = this->expression_list(NULL, false);
      *last_type = type;
      if (*last_expr_list != NULL)
        delete *last_expr_list;
      *last_expr_list = expr_list;
    }

  Expression_list::const_iterator pe = expr_list->begin();
  for (Typed_identifier_list::iterator pi = til.begin();
       pi != til.end();
       ++pi, ++pe)
    {
      if (pe == expr_list->end())
        {
          error_at(this->location(), "not enough initializers");
          return;
        }
      if (type != NULL)
        pi->set_type(type);

      if (!Gogo::is_sink_name(pi->name()))
        this->gogo_->add_constant(*pi, *pe, this->iota_value());
    }
  if (pe != expr_list->end())
    error_at(this->location(), "too many initializers");

  this->increment_iota();

  return;
}

// TypeDecl = "type" Decl<TypeSpec> .

void
Parse::type_decl()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_TYPE));
  this->advance_token();
  this->decl(&Parse::type_spec, NULL);
}

// TypeSpec = identifier Type .

void
Parse::type_spec(void*)
{
  const Token* token = this->peek_token();
  if (!token->is_identifier())
    {
      error_at(this->location(), "expected identifier");
      return;
    }
  std::string name = token->identifier();
  bool is_exported = token->is_identifier_exported();
  source_location location = token->location();
  token = this->advance_token();

  // The scope of the type name starts at the point where the
  // identifier appears in the source code.  We implement this by
  // declaring the type before we read the type definition.
  Named_object* named_type = NULL;
  if (name != "_")
    {
      name = this->gogo_->pack_hidden_name(name, is_exported);
      named_type = this->gogo_->declare_type(name, location);
    }

  Type* type;
  if (!this->peek_token()->is_op(OPERATOR_SEMICOLON))
    type = this->type();
  else
    {
      error_at(this->location(),
               "unexpected semicolon or newline in type declaration");
      type = Type::make_error_type();
      this->advance_token();
    }

  if (type->is_error_type())
    {
      while (!this->peek_token()->is_op(OPERATOR_SEMICOLON)
             && !this->peek_token()->is_eof())
        this->advance_token();
    }

  if (name != "_")
    {
      if (named_type->is_type_declaration())
        {
          Type* ftype = type->forwarded();
          if (ftype->forward_declaration_type() != NULL
              && (ftype->forward_declaration_type()->named_object()
                  == named_type))
            {
              error_at(location, "invalid recursive type");
              type = Type::make_error_type();
            }

          this->gogo_->define_type(named_type,
                                   Type::make_named_type(named_type, type,
                                                         location));
          go_assert(named_type->package() == NULL);
        }
      else
        {
          // This will probably give a redefinition error.
          this->gogo_->add_type(name, type, location);
        }
    }
}

// VarDecl = "var" Decl<VarSpec> .

void
Parse::var_decl()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_VAR));
  this->advance_token();
  this->decl(&Parse::var_spec, NULL);
}

// VarSpec = IdentifierList
//             ( CompleteType [ "=" ExpressionList ] | "=" ExpressionList ) .

void
Parse::var_spec(void*)
{
  // Get the variable names.
  Typed_identifier_list til;
  this->identifier_list(&til);

  source_location location = this->location();

  Type* type = NULL;
  Expression_list* init = NULL;
  if (!this->peek_token()->is_op(OPERATOR_EQ))
    {
      type = this->type();
      if (type->is_error_type())
        {
          while (!this->peek_token()->is_op(OPERATOR_EQ)
                 && !this->peek_token()->is_op(OPERATOR_SEMICOLON)
                 && !this->peek_token()->is_eof())
            this->advance_token();
        }
      if (this->peek_token()->is_op(OPERATOR_EQ))
        {
          this->advance_token();
          init = this->expression_list(NULL, false);
        }
    }
  else
    {
      this->advance_token();
      init = this->expression_list(NULL, false);
    }

  this->init_vars(&til, type, init, false, location);

  if (init != NULL)
    delete init;
}

// Create variables.  TIL is a list of variable names.  If TYPE is not
// NULL, it is the type of all the variables.  If INIT is not NULL, it
// is an initializer list for the variables.

void
Parse::init_vars(const Typed_identifier_list* til, Type* type,
                 Expression_list* init, bool is_coloneq,
                 source_location location)
{
  // Check for an initialization which can yield multiple values.
  if (init != NULL && init->size() == 1 && til->size() > 1)
    {
      if (this->init_vars_from_call(til, type, *init->begin(), is_coloneq,
                                    location))
        return;
      if (this->init_vars_from_map(til, type, *init->begin(), is_coloneq,
                                   location))
        return;
      if (this->init_vars_from_receive(til, type, *init->begin(), is_coloneq,
                                       location))
        return;
      if (this->init_vars_from_type_guard(til, type, *init->begin(),
                                          is_coloneq, location))
        return;
    }

  if (init != NULL && init->size() != til->size())
    {
      if (init->empty() || !init->front()->is_error_expression())
        error_at(location, "wrong number of initializations");
      init = NULL;
      if (type == NULL)
        type = Type::make_error_type();
    }

  // Note that INIT was already parsed with the old name bindings, so
  // we don't have to worry that it will accidentally refer to the
  // newly declared variables.

  Expression_list::const_iterator pexpr;
  if (init != NULL)
    pexpr = init->begin();
  bool any_new = false;
  for (Typed_identifier_list::const_iterator p = til->begin();
       p != til->end();
       ++p)
    {
      if (init != NULL)
        go_assert(pexpr != init->end());
      this->init_var(*p, type, init == NULL ? NULL : *pexpr, is_coloneq,
                     false, &any_new);
      if (init != NULL)
        ++pexpr;
    }
  if (init != NULL)
    go_assert(pexpr == init->end());
  if (is_coloneq && !any_new)
    error_at(location, "variables redeclared but no variable is new");
}

// See if we need to initialize a list of variables from a function
// call.  This returns true if we have set up the variables and the
// initialization.

bool
Parse::init_vars_from_call(const Typed_identifier_list* vars, Type* type,
                           Expression* expr, bool is_coloneq,
                           source_location location)
{
  Call_expression* call = expr->call_expression();
  if (call == NULL)
    return false;

  // This is a function call.  We can't check here whether it returns
  // the right number of values, but it might.  Declare the variables,
  // and then assign the results of the call to them.

  unsigned int index = 0;
  bool any_new = false;
  for (Typed_identifier_list::const_iterator pv = vars->begin();
       pv != vars->end();
       ++pv, ++index)
    {
      Expression* init = Expression::make_call_result(call, index);
      this->init_var(*pv, type, init, is_coloneq, false, &any_new);
    }

  if (is_coloneq && !any_new)
    error_at(location, "variables redeclared but no variable is new");

  return true;
}

// See if we need to initialize a pair of values from a map index
// expression.  This returns true if we have set up the variables and
// the initialization.

bool
Parse::init_vars_from_map(const Typed_identifier_list* vars, Type* type,
                          Expression* expr, bool is_coloneq,
                          source_location location)
{
  Index_expression* index = expr->index_expression();
  if (index == NULL)
    return false;
  if (vars->size() != 2)
    return false;

  // This is an index which is being assigned to two variables.  It
  // must be a map index.  Declare the variables, and then assign the
  // results of the map index.
  bool any_new = false;
  Typed_identifier_list::const_iterator p = vars->begin();
  Expression* init = type == NULL ? index : NULL;
  Named_object* val_no = this->init_var(*p, type, init, is_coloneq,
                                        type == NULL, &any_new);
  if (type == NULL && any_new && val_no->is_variable())
    val_no->var_value()->set_type_from_init_tuple();
  Expression* val_var = Expression::make_var_reference(val_no, location);

  ++p;
  Type* var_type = type;
  if (var_type == NULL)
    var_type = Type::lookup_bool_type();
  Named_object* no = this->init_var(*p, var_type, NULL, is_coloneq, false,
                                    &any_new);
  Expression* present_var = Expression::make_var_reference(no, location);

  if (is_coloneq && !any_new)
    error_at(location, "variables redeclared but no variable is new");

  Statement* s = Statement::make_tuple_map_assignment(val_var, present_var,
                                                      index, location);

  if (!this->gogo_->in_global_scope())
    this->gogo_->add_statement(s);
  else if (!val_no->is_sink())
    {
      if (val_no->is_variable())
        val_no->var_value()->add_preinit_statement(this->gogo_, s);
    }
  else if (!no->is_sink())
    {
      if (no->is_variable())
        no->var_value()->add_preinit_statement(this->gogo_, s);
    }
  else
    {
      // Execute the map index expression just so that we can fail if
      // the map is nil.
      Named_object* dummy = this->create_dummy_global(Type::lookup_bool_type(),
                                                      NULL, location);
      dummy->var_value()->add_preinit_statement(this->gogo_, s);
    }

  return true;
}

// See if we need to initialize a pair of values from a receive
// expression.  This returns true if we have set up the variables and
// the initialization.

bool
Parse::init_vars_from_receive(const Typed_identifier_list* vars, Type* type,
                              Expression* expr, bool is_coloneq,
                              source_location location)
{
  Receive_expression* receive = expr->receive_expression();
  if (receive == NULL)
    return false;
  if (vars->size() != 2)
    return false;

  // This is a receive expression which is being assigned to two
  // variables.  Declare the variables, and then assign the results of
  // the receive.
  bool any_new = false;
  Typed_identifier_list::const_iterator p = vars->begin();
  Expression* init = type == NULL ? receive : NULL;
  Named_object* val_no = this->init_var(*p, type, init, is_coloneq,
                                        type == NULL, &any_new);
  if (type == NULL && any_new && val_no->is_variable())
    val_no->var_value()->set_type_from_init_tuple();
  Expression* val_var = Expression::make_var_reference(val_no, location);

  ++p;
  Type* var_type = type;
  if (var_type == NULL)
    var_type = Type::lookup_bool_type();
  Named_object* no = this->init_var(*p, var_type, NULL, is_coloneq, false,
                                    &any_new);
  Expression* received_var = Expression::make_var_reference(no, location);

  if (is_coloneq && !any_new)
    error_at(location, "variables redeclared but no variable is new");

  Statement* s = Statement::make_tuple_receive_assignment(val_var,
                                                          received_var,
                                                          receive->channel(),
                                                          false,
                                                          location);

  if (!this->gogo_->in_global_scope())
    this->gogo_->add_statement(s);
  else if (!val_no->is_sink())
    {
      if (val_no->is_variable())
        val_no->var_value()->add_preinit_statement(this->gogo_, s);
    }
  else if (!no->is_sink())
    {
      if (no->is_variable())
        no->var_value()->add_preinit_statement(this->gogo_, s);
    }
  else
    {
      Named_object* dummy = this->create_dummy_global(Type::lookup_bool_type(),
                                                      NULL, location);
      dummy->var_value()->add_preinit_statement(this->gogo_, s);
    }

  return true;
}

// See if we need to initialize a pair of values from a type guard
// expression.  This returns true if we have set up the variables and
// the initialization.

bool
Parse::init_vars_from_type_guard(const Typed_identifier_list* vars,
                                 Type* type, Expression* expr,
                                 bool is_coloneq, source_location location)
{
  Type_guard_expression* type_guard = expr->type_guard_expression();
  if (type_guard == NULL)
    return false;
  if (vars->size() != 2)
    return false;

  // This is a type guard expression which is being assigned to two
  // variables.  Declare the variables, and then assign the results of
  // the type guard.
  bool any_new = false;
  Typed_identifier_list::const_iterator p = vars->begin();
  Type* var_type = type;
  if (var_type == NULL)
    var_type = type_guard->type();
  Named_object* val_no = this->init_var(*p, var_type, NULL, is_coloneq, false,
                                        &any_new);
  Expression* val_var = Expression::make_var_reference(val_no, location);

  ++p;
  var_type = type;
  if (var_type == NULL)
    var_type = Type::lookup_bool_type();
  Named_object* no = this->init_var(*p, var_type, NULL, is_coloneq, false,
                                    &any_new);
  Expression* ok_var = Expression::make_var_reference(no, location);

  Expression* texpr = type_guard->expr();
  Type* t = type_guard->type();
  Statement* s = Statement::make_tuple_type_guard_assignment(val_var, ok_var,
                                                             texpr, t,
                                                             location);

  if (is_coloneq && !any_new)
    error_at(location, "variables redeclared but no variable is new");

  if (!this->gogo_->in_global_scope())
    this->gogo_->add_statement(s);
  else if (!val_no->is_sink())
    {
      if (val_no->is_variable())
        val_no->var_value()->add_preinit_statement(this->gogo_, s);
    }
  else if (!no->is_sink())
    {
      if (no->is_variable())
        no->var_value()->add_preinit_statement(this->gogo_, s);
    }
  else
    {
      Named_object* dummy = this->create_dummy_global(type, NULL, location);
      dummy->var_value()->add_preinit_statement(this->gogo_, s);
    }

  return true;
}

// Create a single variable.  If IS_COLONEQ is true, we permit
// redeclarations in the same block, and we set *IS_NEW when we find a
// new variable which is not a redeclaration.

Named_object*
Parse::init_var(const Typed_identifier& tid, Type* type, Expression* init,
                bool is_coloneq, bool type_from_init, bool* is_new)
{
  source_location location = tid.location();

  if (Gogo::is_sink_name(tid.name()))
    {
      if (!type_from_init && init != NULL)
        {
          if (!this->gogo_->in_global_scope())
            this->gogo_->add_statement(Statement::make_statement(init, true));
          else
            return this->create_dummy_global(type, init, location);
        }
      return this->gogo_->add_sink();
    }

  if (is_coloneq)
    {
      Named_object* no = this->gogo_->lookup_in_block(tid.name());
      if (no != NULL
          && (no->is_variable() || no->is_result_variable()))
        {
          // INIT may be NULL even when IS_COLONEQ is true for cases
          // like v, ok := x.(int).
          if (!type_from_init && init != NULL)
            {
              Expression *v = Expression::make_var_reference(no, location);
              Statement *s = Statement::make_assignment(v, init, location);
              this->gogo_->add_statement(s);
            }
          return no;
        }
    }
  *is_new = true;
  Variable* var = new Variable(type, init, this->gogo_->in_global_scope(),
                               false, false, location);
  Named_object* no = this->gogo_->add_variable(tid.name(), var);
  if (!no->is_variable())
    {
      // The name is already defined, so we just gave an error.
      return this->gogo_->add_sink();
    }
  return no;
}

// Create a dummy global variable to force an initializer to be run in
// the right place.  This is used when a sink variable is initialized
// at global scope.

Named_object*
Parse::create_dummy_global(Type* type, Expression* init,
                           source_location location)
{
  if (type == NULL && init == NULL)
    type = Type::lookup_bool_type();
  Variable* var = new Variable(type, init, true, false, false, location);
  static int count;
  char buf[30];
  snprintf(buf, sizeof buf, "_.%d", count);
  ++count;
  return this->gogo_->add_variable(buf, var);
}

// SimpleVarDecl = identifier ":=" Expression .

// We've already seen the identifier.

// FIXME: We also have to implement
//  IdentifierList ":=" ExpressionList
// In order to support both "a, b := 1, 0" and "a, b = 1, 0" we accept
// tuple assignments here as well.

// If P_RANGE_CLAUSE is not NULL, then this will recognize a
// RangeClause.

// If P_TYPE_SWITCH is not NULL, this will recognize a type switch
// guard (var := expr.("type") using the literal keyword "type").

void
Parse::simple_var_decl_or_assignment(const std::string& name,
                                     source_location location,
                                     Range_clause* p_range_clause,
                                     Type_switch* p_type_switch)
{
  Typed_identifier_list til;
  til.push_back(Typed_identifier(name, NULL, location));

  // We've seen one identifier.  If we see a comma now, this could be
  // "a, *p = 1, 2".
  if (this->peek_token()->is_op(OPERATOR_COMMA))
    {
      go_assert(p_type_switch == NULL);
      while (true)
        {
          const Token* token = this->advance_token();
          if (!token->is_identifier())
            break;

          std::string id = token->identifier();
          bool is_id_exported = token->is_identifier_exported();
          source_location id_location = token->location();

          token = this->advance_token();
          if (!token->is_op(OPERATOR_COMMA))
            {
              if (token->is_op(OPERATOR_COLONEQ))
                {
                  id = this->gogo_->pack_hidden_name(id, is_id_exported);
                  til.push_back(Typed_identifier(id, NULL, location));
                }
              else
                this->unget_token(Token::make_identifier_token(id,
                                                               is_id_exported,
                                                               id_location));
              break;
            }

          id = this->gogo_->pack_hidden_name(id, is_id_exported);
          til.push_back(Typed_identifier(id, NULL, location));
        }

      // We have a comma separated list of identifiers in TIL.  If the
      // next token is COLONEQ, then this is a simple var decl, and we
      // have the complete list of identifiers.  If the next token is
      // not COLONEQ, then the only valid parse is a tuple assignment.
      // The list of identifiers we have so far is really a list of
      // expressions.  There are more expressions following.

      if (!this->peek_token()->is_op(OPERATOR_COLONEQ))
        {
          Expression_list* exprs = new Expression_list;
          for (Typed_identifier_list::const_iterator p = til.begin();
               p != til.end();
               ++p)
            exprs->push_back(this->id_to_expression(p->name(),
                                                    p->location()));

          Expression_list* more_exprs = this->expression_list(NULL, true);
          for (Expression_list::const_iterator p = more_exprs->begin();
               p != more_exprs->end();
               ++p)
            exprs->push_back(*p);
          delete more_exprs;

          this->tuple_assignment(exprs, p_range_clause);
          return;
        }
    }

  go_assert(this->peek_token()->is_op(OPERATOR_COLONEQ));
  const Token* token = this->advance_token();

  if (p_range_clause != NULL && token->is_keyword(KEYWORD_RANGE))
    {
      this->range_clause_decl(&til, p_range_clause);
      return;
    }

  Expression_list* init;
  if (p_type_switch == NULL)
    init = this->expression_list(NULL, false);
  else
    {
      bool is_type_switch = false;
      Expression* expr = this->expression(PRECEDENCE_NORMAL, false, true,
                                          &is_type_switch);
      if (is_type_switch)
        {
          p_type_switch->found = true;
          p_type_switch->name = name;
          p_type_switch->location = location;
          p_type_switch->expr = expr;
          return;
        }

      if (!this->peek_token()->is_op(OPERATOR_COMMA))
        {
          init = new Expression_list();
          init->push_back(expr);
        }
      else
        {
          this->advance_token();
          init = this->expression_list(expr, false);
        }
    }

  this->init_vars(&til, NULL, init, true, location);
}

// FunctionDecl = "func" identifier Signature [ Block ] .
// MethodDecl = "func" Receiver identifier Signature [ Block ] .

// gcc extension:
//   FunctionDecl = "func" identifier Signature
//                    __asm__ "(" string_lit ")" .
// This extension means a function whose real name is the identifier
// inside the asm.

void
Parse::function_decl()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_FUNC));
  source_location location = this->location();
  const Token* token = this->advance_token();

  Typed_identifier* rec = NULL;
  if (token->is_op(OPERATOR_LPAREN))
    {
      rec = this->receiver();
      token = this->peek_token();
    }

  if (!token->is_identifier())
    {
      error_at(this->location(), "expected function name");
      return;
    }

  std::string name =
    this->gogo_->pack_hidden_name(token->identifier(),
                                  token->is_identifier_exported());

  this->advance_token();

  Function_type* fntype = this->signature(rec, this->location());
  if (fntype == NULL)
    return;

  Named_object* named_object = NULL;

  if (this->peek_token()->is_keyword(KEYWORD_ASM))
    {
      if (!this->advance_token()->is_op(OPERATOR_LPAREN))
        {
          error_at(this->location(), "expected %<(%>");
          return;
        }
      token = this->advance_token();
      if (!token->is_string())
        {
          error_at(this->location(), "expected string");
          return;
        }
      std::string asm_name = token->string_value();
      if (!this->advance_token()->is_op(OPERATOR_RPAREN))
        {
          error_at(this->location(), "expected %<)%>");
          return;
        }
      this->advance_token();
      if (!Gogo::is_sink_name(name))
        {
          named_object = this->gogo_->declare_function(name, fntype, location);
          if (named_object->is_function_declaration())
            named_object->func_declaration_value()->set_asm_name(asm_name);
        }
    }

  // Check for the easy error of a newline before the opening brace.
  if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
    {
      source_location semi_loc = this->location();
      if (this->advance_token()->is_op(OPERATOR_LCURLY))
        error_at(this->location(),
                 "unexpected semicolon or newline before %<{%>");
      else
        this->unget_token(Token::make_operator_token(OPERATOR_SEMICOLON,
                                                     semi_loc));
    }

  if (!this->peek_token()->is_op(OPERATOR_LCURLY))
    {
      if (named_object == NULL && !Gogo::is_sink_name(name))
        this->gogo_->declare_function(name, fntype, location);
    }
  else
    {
      this->gogo_->start_function(name, fntype, true, location);
      source_location end_loc = this->block();
      this->gogo_->finish_function(end_loc);
    }
}

// Receiver     = "(" [ identifier ] [ "*" ] BaseTypeName ")" .
// BaseTypeName = identifier .

Typed_identifier*
Parse::receiver()
{
  go_assert(this->peek_token()->is_op(OPERATOR_LPAREN));

  std::string name;
  const Token* token = this->advance_token();
  source_location location = token->location();
  if (!token->is_op(OPERATOR_MULT))
    {
      if (!token->is_identifier())
        {
          error_at(this->location(), "method has no receiver");
          while (!token->is_eof() && !token->is_op(OPERATOR_RPAREN))
            token = this->advance_token();
          if (!token->is_eof())
            this->advance_token();
          return NULL;
        }
      name = token->identifier();
      bool is_exported = token->is_identifier_exported();
      token = this->advance_token();
      if (!token->is_op(OPERATOR_DOT) && !token->is_op(OPERATOR_RPAREN))
        {
          // An identifier followed by something other than a dot or a
          // right parenthesis must be a receiver name followed by a
          // type.
          name = this->gogo_->pack_hidden_name(name, is_exported);
        }
      else
        {
          // This must be a type name.
          this->unget_token(Token::make_identifier_token(name, is_exported,
                                                         location));
          token = this->peek_token();
          name.clear();
        }
    }

  // Here the receiver name is in NAME (it is empty if the receiver is
  // unnamed) and TOKEN is the first token in the type.

  bool is_pointer = false;
  if (token->is_op(OPERATOR_MULT))
    {
      is_pointer = true;
      token = this->advance_token();
    }

  if (!token->is_identifier())
    {
      error_at(this->location(), "expected receiver name or type");
      int c = token->is_op(OPERATOR_LPAREN) ? 1 : 0;
      while (!token->is_eof())
        {
          token = this->advance_token();
          if (token->is_op(OPERATOR_LPAREN))
            ++c;
          else if (token->is_op(OPERATOR_RPAREN))
            {
              if (c == 0)
                break;
              --c;
            }
        }
      if (!token->is_eof())
        this->advance_token();
      return NULL;
    }

  Type* type = this->type_name(true);

  if (is_pointer && !type->is_error_type())
    type = Type::make_pointer_type(type);

  if (this->peek_token()->is_op(OPERATOR_RPAREN))
    this->advance_token();
  else
    {
      if (this->peek_token()->is_op(OPERATOR_COMMA))
        error_at(this->location(), "method has multiple receivers");
      else
        error_at(this->location(), "expected %<)%>");
      while (!token->is_eof() && !token->is_op(OPERATOR_RPAREN))
        token = this->advance_token();
      if (!token->is_eof())
        this->advance_token();
      return NULL;
    }

  return new Typed_identifier(name, type, location);
}

// Operand    = Literal | QualifiedIdent | MethodExpr | "(" Expression ")" .
// Literal    = BasicLit | CompositeLit | FunctionLit .
// BasicLit   = int_lit | float_lit | imaginary_lit | char_lit | string_lit .

// If MAY_BE_SINK is true, this operand may be "_".

Expression*
Parse::operand(bool may_be_sink)
{
  const Token* token = this->peek_token();
  Expression* ret;
  switch (token->classification())
    {
    case Token::TOKEN_IDENTIFIER:
      {
        source_location location = token->location();
        std::string id = token->identifier();
        bool is_exported = token->is_identifier_exported();
        std::string packed = this->gogo_->pack_hidden_name(id, is_exported);

        Named_object* in_function;
        Named_object* named_object = this->gogo_->lookup(packed, &in_function);

        Package* package = NULL;
        if (named_object != NULL && named_object->is_package())
          {
            if (!this->advance_token()->is_op(OPERATOR_DOT)
                || !this->advance_token()->is_identifier())
              {
                error_at(location, "unexpected reference to package");
                return Expression::make_error(location);
              }
            package = named_object->package_value();
            package->set_used();
            id = this->peek_token()->identifier();
            is_exported = this->peek_token()->is_identifier_exported();
            packed = this->gogo_->pack_hidden_name(id, is_exported);
            named_object = package->lookup(packed);
            location = this->location();
            go_assert(in_function == NULL);
          }

        this->advance_token();

        if (named_object != NULL
            && named_object->is_type()
            && !named_object->type_value()->is_visible())
          {
            go_assert(package != NULL);
            error_at(location, "invalid reference to hidden type %<%s.%s%>",
                     Gogo::message_name(package->name()).c_str(),
                     Gogo::message_name(id).c_str());
            return Expression::make_error(location);
          }


        if (named_object == NULL)
          {
            if (package != NULL)
              {
                std::string n1 = Gogo::message_name(package->name());
                std::string n2 = Gogo::message_name(id);
                if (!is_exported)
                  error_at(location,
                           ("invalid reference to unexported identifier "
                            "%<%s.%s%>"),
                           n1.c_str(), n2.c_str());
                else
                  error_at(location,
                           "reference to undefined identifier %<%s.%s%>",
                           n1.c_str(), n2.c_str());
                return Expression::make_error(location);
              }

            named_object = this->gogo_->add_unknown_name(packed, location);
          }

        if (in_function != NULL
            && in_function != this->gogo_->current_function()
            && (named_object->is_variable()
                || named_object->is_result_variable()))
          return this->enclosing_var_reference(in_function, named_object,
                                               location);

        switch (named_object->classification())
          {
          case Named_object::NAMED_OBJECT_CONST:
            return Expression::make_const_reference(named_object, location);
          case Named_object::NAMED_OBJECT_TYPE:
            return Expression::make_type(named_object->type_value(), location);
          case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
            {
              Type* t = Type::make_forward_declaration(named_object);
              return Expression::make_type(t, location);
            }
          case Named_object::NAMED_OBJECT_VAR:
          case Named_object::NAMED_OBJECT_RESULT_VAR:
            return Expression::make_var_reference(named_object, location);
          case Named_object::NAMED_OBJECT_SINK:
            if (may_be_sink)
              return Expression::make_sink(location);
            else
              {
                error_at(location, "cannot use _ as value");
                return Expression::make_error(location);
              }
          case Named_object::NAMED_OBJECT_FUNC:
          case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
            return Expression::make_func_reference(named_object, NULL,
                                                   location);
          case Named_object::NAMED_OBJECT_UNKNOWN:
            return Expression::make_unknown_reference(named_object, location);
          default:
            go_unreachable();
          }
      }
      go_unreachable();

    case Token::TOKEN_STRING:
      ret = Expression::make_string(token->string_value(), token->location());
      this->advance_token();
      return ret;

    case Token::TOKEN_INTEGER:
      ret = Expression::make_integer(token->integer_value(), NULL,
                                     token->location());
      this->advance_token();
      return ret;

    case Token::TOKEN_FLOAT:
      ret = Expression::make_float(token->float_value(), NULL,
                                   token->location());
      this->advance_token();
      return ret;

    case Token::TOKEN_IMAGINARY:
      {
        mpfr_t zero;
        mpfr_init_set_ui(zero, 0, GMP_RNDN);
        ret = Expression::make_complex(&zero, token->imaginary_value(),
                                       NULL, token->location());
        mpfr_clear(zero);
        this->advance_token();
        return ret;
      }

    case Token::TOKEN_KEYWORD:
      switch (token->keyword())
        {
        case KEYWORD_FUNC:
          return this->function_lit();
        case KEYWORD_CHAN:
        case KEYWORD_INTERFACE:
        case KEYWORD_MAP:
        case KEYWORD_STRUCT:
          {
            source_location location = token->location();
            return Expression::make_type(this->type(), location);
          }
        default:
          break;
        }
      break;

    case Token::TOKEN_OPERATOR:
      if (token->is_op(OPERATOR_LPAREN))
        {
          this->advance_token();
          ret = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
          if (!this->peek_token()->is_op(OPERATOR_RPAREN))
            error_at(this->location(), "missing %<)%>");
          else
            this->advance_token();
          return ret;
        }
      else if (token->is_op(OPERATOR_LSQUARE))
        {
          // Here we call array_type directly, as this is the only
          // case where an ellipsis is permitted for an array type.
          source_location location = token->location();
          return Expression::make_type(this->array_type(true), location);
        }
      break;

    default:
      break;
    }

  error_at(this->location(), "expected operand");
  return Expression::make_error(this->location());
}

// Handle a reference to a variable in an enclosing function.  We add
// it to a list of such variables.  We return a reference to a field
// in a struct which will be passed on the static chain when calling
// the current function.

Expression*
Parse::enclosing_var_reference(Named_object* in_function, Named_object* var,
                               source_location location)
{
  go_assert(var->is_variable() || var->is_result_variable());

  Named_object* this_function = this->gogo_->current_function();
  Named_object* closure = this_function->func_value()->closure_var();

  Enclosing_var ev(var, in_function, this->enclosing_vars_.size());
  std::pair<Enclosing_vars::iterator, bool> ins =
    this->enclosing_vars_.insert(ev);
  if (ins.second)
    {
      // This is a variable we have not seen before.  Add a new field
      // to the closure type.
      this_function->func_value()->add_closure_field(var, location);
    }

  Expression* closure_ref = Expression::make_var_reference(closure,
                                                           location);
  closure_ref = Expression::make_unary(OPERATOR_MULT, closure_ref, location);

  // The closure structure holds pointers to the variables, so we need
  // to introduce an indirection.
  Expression* e = Expression::make_field_reference(closure_ref,
                                                   ins.first->index(),
                                                   location);
  e = Expression::make_unary(OPERATOR_MULT, e, location);
  return e;
}

// CompositeLit  = LiteralType LiteralValue .
// LiteralType   = StructType | ArrayType | "[" "..." "]" ElementType |
//                 SliceType | MapType | TypeName .
// LiteralValue  = "{" [ ElementList [ "," ] ] "}" .
// ElementList   = Element { "," Element } .
// Element       = [ Key ":" ] Value .
// Key           = FieldName | ElementIndex .
// FieldName     = identifier .
// ElementIndex  = Expression .
// Value         = Expression | LiteralValue .

// We have already seen the type if there is one, and we are now
// looking at the LiteralValue.  The case "[" "..."  "]" ElementType
// will be seen here as an array type whose length is "nil".  The
// DEPTH parameter is non-zero if this is an embedded composite
// literal and the type was omitted.  It gives the number of steps up
// to the type which was provided.  E.g., in [][]int{{1}} it will be
// 1.  In [][][]int{{{1}}} it will be 2.

Expression*
Parse::composite_lit(Type* type, int depth, source_location location)
{
  go_assert(this->peek_token()->is_op(OPERATOR_LCURLY));
  this->advance_token();

  if (this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      this->advance_token();
      return Expression::make_composite_literal(type, depth, false, NULL,
                                                location);
    }

  bool has_keys = false;
  Expression_list* vals = new Expression_list;
  while (true)
    {
      Expression* val;
      bool is_type_omitted = false;

      const Token* token = this->peek_token();

      if (token->is_identifier())
        {
          std::string identifier = token->identifier();
          bool is_exported = token->is_identifier_exported();
          source_location location = token->location();

          if (this->advance_token()->is_op(OPERATOR_COLON))
            {
              // This may be a field name.  We don't know for sure--it
              // could also be an expression for an array index.  We
              // don't want to parse it as an expression because may
              // trigger various errors, e.g., if this identifier
              // happens to be the name of a package.
              Gogo* gogo = this->gogo_;
              val = this->id_to_expression(gogo->pack_hidden_name(identifier,
                                                                  is_exported),
                                           location);
            }
          else
            {
              this->unget_token(Token::make_identifier_token(identifier,
                                                             is_exported,
                                                             location));
              val = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
            }
        }
      else if (!token->is_op(OPERATOR_LCURLY))
        val = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
      else
        {
          // This must be a composite literal inside another composite
          // literal, with the type omitted for the inner one.
          val = this->composite_lit(type, depth + 1, token->location());
          is_type_omitted = true;
        }

      token = this->peek_token();
      if (!token->is_op(OPERATOR_COLON))
        {
          if (has_keys)
            vals->push_back(NULL);
        }
      else
        {
          if (is_type_omitted && !val->is_error_expression())
            {
              error_at(this->location(), "unexpected %<:%>");
              val = Expression::make_error(this->location());
            }

          this->advance_token();

          if (!has_keys && !vals->empty())
            {
              Expression_list* newvals = new Expression_list;
              for (Expression_list::const_iterator p = vals->begin();
                   p != vals->end();
                   ++p)
                {
                  newvals->push_back(NULL);
                  newvals->push_back(*p);
                }
              delete vals;
              vals = newvals;
            }
          has_keys = true;

          if (val->unknown_expression() != NULL)
            val->unknown_expression()->set_is_composite_literal_key();

          vals->push_back(val);

          if (!token->is_op(OPERATOR_LCURLY))
            val = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
          else
            {
              // This must be a composite literal inside another
              // composite literal, with the type omitted for the
              // inner one.
              val = this->composite_lit(type, depth + 1, token->location());
            }

          token = this->peek_token();
        }

      vals->push_back(val);

      if (token->is_op(OPERATOR_COMMA))
        {
          if (this->advance_token()->is_op(OPERATOR_RCURLY))
            {
              this->advance_token();
              break;
            }
        }
      else if (token->is_op(OPERATOR_RCURLY))
        {
          this->advance_token();
          break;
        }
      else
        {
          error_at(this->location(), "expected %<,%> or %<}%>");

          int depth = 0;
          while (!token->is_eof()
                 && (depth > 0 || !token->is_op(OPERATOR_RCURLY)))
            {
              if (token->is_op(OPERATOR_LCURLY))
                ++depth;
              else if (token->is_op(OPERATOR_RCURLY))
                --depth;
              token = this->advance_token();
            }
          if (token->is_op(OPERATOR_RCURLY))
            this->advance_token();

          return Expression::make_error(location);
        }
    }

  return Expression::make_composite_literal(type, depth, has_keys, vals,
                                            location);
}

// FunctionLit = "func" Signature Block .

Expression*
Parse::function_lit()
{
  source_location location = this->location();
  go_assert(this->peek_token()->is_keyword(KEYWORD_FUNC));
  this->advance_token();

  Enclosing_vars hold_enclosing_vars;
  hold_enclosing_vars.swap(this->enclosing_vars_);

  Function_type* type = this->signature(NULL, location);
  if (type == NULL)
    type = Type::make_function_type(NULL, NULL, NULL, location);

  // For a function literal, the next token must be a '{'.  If we
  // don't see that, then we may have a type expression.
  if (!this->peek_token()->is_op(OPERATOR_LCURLY))
    return Expression::make_type(type, location);

  Bc_stack* hold_break_stack = this->break_stack_;
  Bc_stack* hold_continue_stack = this->continue_stack_;
  this->break_stack_ = NULL;
  this->continue_stack_ = NULL;

  Named_object* no = this->gogo_->start_function("", type, true, location);

  source_location end_loc = this->block();

  this->gogo_->finish_function(end_loc);

  if (this->break_stack_ != NULL)
    delete this->break_stack_;
  if (this->continue_stack_ != NULL)
    delete this->continue_stack_;
  this->break_stack_ = hold_break_stack;
  this->continue_stack_ = hold_continue_stack;

  hold_enclosing_vars.swap(this->enclosing_vars_);

  Expression* closure = this->create_closure(no, &hold_enclosing_vars,
                                             location);

  return Expression::make_func_reference(no, closure, location);
}

// Create a closure for the nested function FUNCTION.  This is based
// on ENCLOSING_VARS, which is a list of all variables defined in
// enclosing functions and referenced from FUNCTION.  A closure is the
// address of a struct which contains the addresses of all the
// referenced variables.  This returns NULL if no closure is required.

Expression*
Parse::create_closure(Named_object* function, Enclosing_vars* enclosing_vars,
                      source_location location)
{
  if (enclosing_vars->empty())
    return NULL;

  // Get the variables in order by their field index.

  size_t enclosing_var_count = enclosing_vars->size();
  std::vector<Enclosing_var> ev(enclosing_var_count);
  for (Enclosing_vars::const_iterator p = enclosing_vars->begin();
       p != enclosing_vars->end();
       ++p)
    ev[p->index()] = *p;

  // Build an initializer for a composite literal of the closure's
  // type.

  Named_object* enclosing_function = this->gogo_->current_function();
  Expression_list* initializer = new Expression_list;
  for (size_t i = 0; i < enclosing_var_count; ++i)
    {
      go_assert(ev[i].index() == i);
      Named_object* var = ev[i].var();
      Expression* ref;
      if (ev[i].in_function() == enclosing_function)
        ref = Expression::make_var_reference(var, location);
      else
        ref = this->enclosing_var_reference(ev[i].in_function(), var,
                                            location);
      Expression* refaddr = Expression::make_unary(OPERATOR_AND, ref,
                                                   location);
      initializer->push_back(refaddr);
    }

  Named_object* closure_var = function->func_value()->closure_var();
  Struct_type* st = closure_var->var_value()->type()->deref()->struct_type();
  Expression* cv = Expression::make_struct_composite_literal(st, initializer,
                                                             location);
  return Expression::make_heap_composite(cv, location);
}

// PrimaryExpr = Operand { Selector | Index | Slice | TypeGuard | Call } .

// If MAY_BE_SINK is true, this expression may be "_".

// If MAY_BE_COMPOSITE_LIT is true, this expression may be a composite
// literal.

// If IS_TYPE_SWITCH is not NULL, this will recognize a type switch
// guard (var := expr.("type") using the literal keyword "type").

Expression*
Parse::primary_expr(bool may_be_sink, bool may_be_composite_lit,
                    bool* is_type_switch)
{
  source_location start_loc = this->location();
  bool is_parenthesized = this->peek_token()->is_op(OPERATOR_LPAREN);

  Expression* ret = this->operand(may_be_sink);

  // An unknown name followed by a curly brace must be a composite
  // literal, and the unknown name must be a type.
  if (may_be_composite_lit
      && !is_parenthesized
      && ret->unknown_expression() != NULL
      && this->peek_token()->is_op(OPERATOR_LCURLY))
    {
      Named_object* no = ret->unknown_expression()->named_object();
      Type* type = Type::make_forward_declaration(no);
      ret = Expression::make_type(type, ret->location());
    }

  // We handle composite literals and type casts here, as it is the
  // easiest way to handle types which are in parentheses, as in
  // "((uint))(1)".
  if (ret->is_type_expression())
    {
      if (this->peek_token()->is_op(OPERATOR_LCURLY))
        {
          if (is_parenthesized)
            error_at(start_loc,
                     "cannot parenthesize type in composite literal");
          ret = this->composite_lit(ret->type(), 0, ret->location());
        }
      else if (this->peek_token()->is_op(OPERATOR_LPAREN))
        {
          source_location loc = this->location();
          this->advance_token();
          Expression* expr = this->expression(PRECEDENCE_NORMAL, false, true,
                                              NULL);
          if (this->peek_token()->is_op(OPERATOR_ELLIPSIS))
            {
              error_at(this->location(),
                       "invalid use of %<...%> in type conversion");
              this->advance_token();
            }
          if (!this->peek_token()->is_op(OPERATOR_RPAREN))
            error_at(this->location(), "expected %<)%>");
          else
            this->advance_token();
          if (expr->is_error_expression())
            ret = expr;
          else
            {
              Type* t = ret->type();
              if (t->classification() == Type::TYPE_ARRAY
                  && t->array_type()->length() != NULL
                  && t->array_type()->length()->is_nil_expression())
                {
                  error_at(ret->location(),
                           "invalid use of %<...%> in type conversion");
                  ret = Expression::make_error(loc);
                }
              else
                ret = Expression::make_cast(t, expr, loc);
            }
        }
    }

  while (true)
    {
      const Token* token = this->peek_token();
      if (token->is_op(OPERATOR_LPAREN))
        ret = this->call(this->verify_not_sink(ret));
      else if (token->is_op(OPERATOR_DOT))
        {
          ret = this->selector(this->verify_not_sink(ret), is_type_switch);
          if (is_type_switch != NULL && *is_type_switch)
            break;
        }
      else if (token->is_op(OPERATOR_LSQUARE))
        ret = this->index(this->verify_not_sink(ret));
      else
        break;
    }

  return ret;
}

// Selector = "." identifier .
// TypeGuard = "." "(" QualifiedIdent ")" .

// Note that Operand can expand to QualifiedIdent, which contains a
// ".".  That is handled directly in operand when it sees a package
// name.

// If IS_TYPE_SWITCH is not NULL, this will recognize a type switch
// guard (var := expr.("type") using the literal keyword "type").

Expression*
Parse::selector(Expression* left, bool* is_type_switch)
{
  go_assert(this->peek_token()->is_op(OPERATOR_DOT));
  source_location location = this->location();

  const Token* token = this->advance_token();
  if (token->is_identifier())
    {
      // This could be a field in a struct, or a method in an
      // interface, or a method associated with a type.  We can't know
      // which until we have seen all the types.
      std::string name =
        this->gogo_->pack_hidden_name(token->identifier(),
                                      token->is_identifier_exported());
      if (token->identifier() == "_")
        {
          error_at(this->location(), "invalid use of %<_%>");
          name = this->gogo_->pack_hidden_name("blank", false);
        }
      this->advance_token();
      return Expression::make_selector(left, name, location);
    }
  else if (token->is_op(OPERATOR_LPAREN))
    {
      this->advance_token();
      Type* type = NULL;
      if (!this->peek_token()->is_keyword(KEYWORD_TYPE))
        type = this->type();
      else
        {
          if (is_type_switch != NULL)
            *is_type_switch = true;
          else
            {
              error_at(this->location(),
                       "use of %<.(type)%> outside type switch");
              type = Type::make_error_type();
            }
          this->advance_token();
        }
      if (!this->peek_token()->is_op(OPERATOR_RPAREN))
        error_at(this->location(), "missing %<)%>");
      else
        this->advance_token();
      if (is_type_switch != NULL && *is_type_switch)
        return left;
      return Expression::make_type_guard(left, type, location);
    }
  else
    {
      error_at(this->location(), "expected identifier or %<(%>");
      return left;
    }
}

// Index          = "[" Expression "]" .
// Slice          = "[" Expression ":" [ Expression ] "]" .

Expression*
Parse::index(Expression* expr)
{
  source_location location = this->location();
  go_assert(this->peek_token()->is_op(OPERATOR_LSQUARE));
  this->advance_token();

  Expression* start;
  if (!this->peek_token()->is_op(OPERATOR_COLON))
    start = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
  else
    {
      mpz_t zero;
      mpz_init_set_ui(zero, 0);
      start = Expression::make_integer(&zero, NULL, location);
      mpz_clear(zero);
    }

  Expression* end = NULL;
  if (this->peek_token()->is_op(OPERATOR_COLON))
    {
      // We use nil to indicate a missing high expression.
      if (this->advance_token()->is_op(OPERATOR_RSQUARE))
        end = Expression::make_nil(this->location());
      else
        end = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
    }
  if (!this->peek_token()->is_op(OPERATOR_RSQUARE))
    error_at(this->location(), "missing %<]%>");
  else
    this->advance_token();
  return Expression::make_index(expr, start, end, location);
}

// Call           = "(" [ ArgumentList [ "," ] ] ")" .
// ArgumentList   = ExpressionList [ "..." ] .

Expression*
Parse::call(Expression* func)
{
  go_assert(this->peek_token()->is_op(OPERATOR_LPAREN));
  Expression_list* args = NULL;
  bool is_varargs = false;
  const Token* token = this->advance_token();
  if (!token->is_op(OPERATOR_RPAREN))
    {
      args = this->expression_list(NULL, false);
      token = this->peek_token();
      if (token->is_op(OPERATOR_ELLIPSIS))
        {
          is_varargs = true;
          token = this->advance_token();
        }
    }
  if (token->is_op(OPERATOR_COMMA))
    token = this->advance_token();
  if (!token->is_op(OPERATOR_RPAREN))
    error_at(this->location(), "missing %<)%>");
  else
    this->advance_token();
  if (func->is_error_expression())
    return func;
  return Expression::make_call(func, args, is_varargs, func->location());
}

// Return an expression for a single unqualified identifier.

Expression*
Parse::id_to_expression(const std::string& name, source_location location)
{
  Named_object* in_function;
  Named_object* named_object = this->gogo_->lookup(name, &in_function);
  if (named_object == NULL)
    named_object = this->gogo_->add_unknown_name(name, location);

  if (in_function != NULL
      && in_function != this->gogo_->current_function()
      && (named_object->is_variable() || named_object->is_result_variable()))
    return this->enclosing_var_reference(in_function, named_object,
                                         location);

  switch (named_object->classification())
    {
    case Named_object::NAMED_OBJECT_CONST:
      return Expression::make_const_reference(named_object, location);
    case Named_object::NAMED_OBJECT_VAR:
    case Named_object::NAMED_OBJECT_RESULT_VAR:
      return Expression::make_var_reference(named_object, location);
    case Named_object::NAMED_OBJECT_SINK:
      return Expression::make_sink(location);
    case Named_object::NAMED_OBJECT_FUNC:
    case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
      return Expression::make_func_reference(named_object, NULL, location);
    case Named_object::NAMED_OBJECT_UNKNOWN:
      return Expression::make_unknown_reference(named_object, location);
    case Named_object::NAMED_OBJECT_PACKAGE:
    case Named_object::NAMED_OBJECT_TYPE:
    case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
      // These cases can arise for a field name in a composite
      // literal.
      return Expression::make_unknown_reference(named_object, location);
    default:
      error_at(this->location(), "unexpected type of identifier");
      return Expression::make_error(location);
    }
}

// Expression = UnaryExpr { binary_op Expression } .

// PRECEDENCE is the precedence of the current operator.

// If MAY_BE_SINK is true, this expression may be "_".

// If MAY_BE_COMPOSITE_LIT is true, this expression may be a composite
// literal.

// If IS_TYPE_SWITCH is not NULL, this will recognize a type switch
// guard (var := expr.("type") using the literal keyword "type").

Expression*
Parse::expression(Precedence precedence, bool may_be_sink,
                  bool may_be_composite_lit, bool* is_type_switch)
{
  Expression* left = this->unary_expr(may_be_sink, may_be_composite_lit,
                                      is_type_switch);

  while (true)
    {
      if (is_type_switch != NULL && *is_type_switch)
        return left;

      const Token* token = this->peek_token();
      if (token->classification() != Token::TOKEN_OPERATOR)
        {
          // Not a binary_op.
          return left;
        }

      Precedence right_precedence;
      switch (token->op())
        {
        case OPERATOR_OROR:
          right_precedence = PRECEDENCE_OROR;
          break;
        case OPERATOR_ANDAND:
          right_precedence = PRECEDENCE_ANDAND;
          break;
        case OPERATOR_EQEQ:
        case OPERATOR_NOTEQ:
        case OPERATOR_LT:
        case OPERATOR_LE:
        case OPERATOR_GT:
        case OPERATOR_GE:
          right_precedence = PRECEDENCE_RELOP;
          break;
        case OPERATOR_PLUS:
        case OPERATOR_MINUS:
        case OPERATOR_OR:
        case OPERATOR_XOR:
          right_precedence = PRECEDENCE_ADDOP;
          break;
        case OPERATOR_MULT:
        case OPERATOR_DIV:
        case OPERATOR_MOD:
        case OPERATOR_LSHIFT:
        case OPERATOR_RSHIFT:
        case OPERATOR_AND:
        case OPERATOR_BITCLEAR:
          right_precedence = PRECEDENCE_MULOP;
          break;
        default:
          right_precedence = PRECEDENCE_INVALID;
          break;
        }

      if (right_precedence == PRECEDENCE_INVALID)
        {
          // Not a binary_op.
          return left;
        }

      Operator op = token->op();
      source_location binop_location = token->location();

      if (precedence >= right_precedence)
        {
          // We've already seen A * B, and we see + C.  We want to
          // return so that A * B becomes a group.
          return left;
        }

      this->advance_token();

      left = this->verify_not_sink(left);
      Expression* right = this->expression(right_precedence, false,
                                           may_be_composite_lit,
                                           NULL);
      left = Expression::make_binary(op, left, right, binop_location);
    }
}

bool
Parse::expression_may_start_here()
{
  const Token* token = this->peek_token();
  switch (token->classification())
    {
    case Token::TOKEN_INVALID:
    case Token::TOKEN_EOF:
      return false;
    case Token::TOKEN_KEYWORD:
      switch (token->keyword())
        {
        case KEYWORD_CHAN:
        case KEYWORD_FUNC:
        case KEYWORD_MAP:
        case KEYWORD_STRUCT:
        case KEYWORD_INTERFACE:
          return true;
        default:
          return false;
        }
    case Token::TOKEN_IDENTIFIER:
      return true;
    case Token::TOKEN_STRING:
      return true;
    case Token::TOKEN_OPERATOR:
      switch (token->op())
        {
        case OPERATOR_PLUS:
        case OPERATOR_MINUS:
        case OPERATOR_NOT:
        case OPERATOR_XOR:
        case OPERATOR_MULT:
        case OPERATOR_CHANOP:
        case OPERATOR_AND:
        case OPERATOR_LPAREN:
        case OPERATOR_LSQUARE:
          return true;
        default:
          return false;
        }
    case Token::TOKEN_INTEGER:
    case Token::TOKEN_FLOAT:
    case Token::TOKEN_IMAGINARY:
      return true;
    default:
      go_unreachable();
    }
}

// UnaryExpr = unary_op UnaryExpr | PrimaryExpr .

// If MAY_BE_SINK is true, this expression may be "_".

// If MAY_BE_COMPOSITE_LIT is true, this expression may be a composite
// literal.

// If IS_TYPE_SWITCH is not NULL, this will recognize a type switch
// guard (var := expr.("type") using the literal keyword "type").

Expression*
Parse::unary_expr(bool may_be_sink, bool may_be_composite_lit,
                  bool* is_type_switch)
{
  const Token* token = this->peek_token();
  if (token->is_op(OPERATOR_PLUS)
      || token->is_op(OPERATOR_MINUS)
      || token->is_op(OPERATOR_NOT)
      || token->is_op(OPERATOR_XOR)
      || token->is_op(OPERATOR_CHANOP)
      || token->is_op(OPERATOR_MULT)
      || token->is_op(OPERATOR_AND))
    {
      source_location location = token->location();
      Operator op = token->op();
      this->advance_token();

      if (op == OPERATOR_CHANOP
          && this->peek_token()->is_keyword(KEYWORD_CHAN))
        {
          // This is "<- chan" which must be the start of a type.
          this->unget_token(Token::make_operator_token(op, location));
          return Expression::make_type(this->type(), location);
        }

      Expression* expr = this->unary_expr(false, may_be_composite_lit, NULL);
      if (expr->is_error_expression())
        ;
      else if (op == OPERATOR_MULT && expr->is_type_expression())
        expr = Expression::make_type(Type::make_pointer_type(expr->type()),
                                     location);
      else if (op == OPERATOR_AND && expr->is_composite_literal())
        expr = Expression::make_heap_composite(expr, location);
      else if (op != OPERATOR_CHANOP)
        expr = Expression::make_unary(op, expr, location);
      else
        expr = Expression::make_receive(expr, location);
      return expr;
    }
  else
    return this->primary_expr(may_be_sink, may_be_composite_lit,
                              is_type_switch);
}

// Statement =
//      Declaration | LabeledStmt | SimpleStmt |
//      GoStmt | ReturnStmt | BreakStmt | ContinueStmt | GotoStmt |
//      FallthroughStmt | Block | IfStmt | SwitchStmt | SelectStmt | ForStmt |
//      DeferStmt .

// LABEL is the label of this statement if it has one.

void
Parse::statement(Label* label)
{
  const Token* token = this->peek_token();
  switch (token->classification())
    {
    case Token::TOKEN_KEYWORD:
      {
        switch (token->keyword())
          {
          case KEYWORD_CONST:
          case KEYWORD_TYPE:
          case KEYWORD_VAR:
            this->declaration();
            break;
          case KEYWORD_FUNC:
          case KEYWORD_MAP:
          case KEYWORD_STRUCT:
          case KEYWORD_INTERFACE:
            this->simple_stat(true, NULL, NULL, NULL);
            break;
          case KEYWORD_GO:
          case KEYWORD_DEFER:
            this->go_or_defer_stat();
            break;
          case KEYWORD_RETURN:
            this->return_stat();
            break;
          case KEYWORD_BREAK:
            this->break_stat();
            break;
          case KEYWORD_CONTINUE:
            this->continue_stat();
            break;
          case KEYWORD_GOTO:
            this->goto_stat();
            break;
          case KEYWORD_IF:
            this->if_stat();
            break;
          case KEYWORD_SWITCH:
            this->switch_stat(label);
            break;
          case KEYWORD_SELECT:
            this->select_stat(label);
            break;
          case KEYWORD_FOR:
            this->for_stat(label);
            break;
          default:
            error_at(this->location(), "expected statement");
            this->advance_token();
            break;
          }
      }
      break;

    case Token::TOKEN_IDENTIFIER:
      {
        std::string identifier = token->identifier();
        bool is_exported = token->is_identifier_exported();
        source_location location = token->location();
        if (this->advance_token()->is_op(OPERATOR_COLON))
          {
            this->advance_token();
            this->labeled_stmt(identifier, location);
          }
        else
          {
            this->unget_token(Token::make_identifier_token(identifier,
                                                           is_exported,
                                                           location));
            this->simple_stat(true, NULL, NULL, NULL);
          }
      }
      break;

    case Token::TOKEN_OPERATOR:
      if (token->is_op(OPERATOR_LCURLY))
        {
          source_location location = token->location();
          this->gogo_->start_block(location);
          source_location end_loc = this->block();
          this->gogo_->add_block(this->gogo_->finish_block(end_loc),
                                 location);
        }
      else if (!token->is_op(OPERATOR_SEMICOLON))
        this->simple_stat(true, NULL, NULL, NULL);
      break;

    case Token::TOKEN_STRING:
    case Token::TOKEN_INTEGER:
    case Token::TOKEN_FLOAT:
    case Token::TOKEN_IMAGINARY:
      this->simple_stat(true, NULL, NULL, NULL);
      break;

    default:
      error_at(this->location(), "expected statement");
      this->advance_token();
      break;
    }
}

bool
Parse::statement_may_start_here()
{
  const Token* token = this->peek_token();
  switch (token->classification())
    {
    case Token::TOKEN_KEYWORD:
      {
        switch (token->keyword())
          {
          case KEYWORD_CONST:
          case KEYWORD_TYPE:
          case KEYWORD_VAR:
          case KEYWORD_FUNC:
          case KEYWORD_MAP:
          case KEYWORD_STRUCT:
          case KEYWORD_INTERFACE:
          case KEYWORD_GO:
          case KEYWORD_DEFER:
          case KEYWORD_RETURN:
          case KEYWORD_BREAK:
          case KEYWORD_CONTINUE:
          case KEYWORD_GOTO:
          case KEYWORD_IF:
          case KEYWORD_SWITCH:
          case KEYWORD_SELECT:
          case KEYWORD_FOR:
            return true;

          default:
            return false;
          }
      }
      break;

    case Token::TOKEN_IDENTIFIER:
      return true;

    case Token::TOKEN_OPERATOR:
      if (token->is_op(OPERATOR_LCURLY)
          || token->is_op(OPERATOR_SEMICOLON))
        return true;
      else
        return this->expression_may_start_here();

    case Token::TOKEN_STRING:
    case Token::TOKEN_INTEGER:
    case Token::TOKEN_FLOAT:
    case Token::TOKEN_IMAGINARY:
      return true;

    default:
      return false;
    }
}

// LabeledStmt = Label ":" Statement .
// Label       = identifier .

void
Parse::labeled_stmt(const std::string& label_name, source_location location)
{
  Label* label = this->gogo_->add_label_definition(label_name, location);

  if (this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      // This is a label at the end of a block.  A program is
      // permitted to omit a semicolon here.
      return;
    }

  if (!this->statement_may_start_here())
    {
      // Mark the label as used to avoid a useless error about an
      // unused label.
      label->set_is_used();

      error_at(location, "missing statement after label");
      this->unget_token(Token::make_operator_token(OPERATOR_SEMICOLON,
                                                   location));
      return;
    }

  this->statement(label);
}

// SimpleStmt = EmptyStmt | ExpressionStmt | SendStmt | IncDecStmt |
//      Assignment | ShortVarDecl .

// EmptyStmt was handled in Parse::statement.

// In order to make this work for if and switch statements, if
// RETURN_EXP is not NULL, and we see an ExpressionStat, we return the
// expression rather than adding an expression statement to the
// current block.  If we see something other than an ExpressionStat,
// we add the statement, set *RETURN_EXP to true if we saw a send
// statement, and return NULL.  The handling of send statements is for
// better error messages.

// If P_RANGE_CLAUSE is not NULL, then this will recognize a
// RangeClause.

// If P_TYPE_SWITCH is not NULL, this will recognize a type switch
// guard (var := expr.("type") using the literal keyword "type").

Expression*
Parse::simple_stat(bool may_be_composite_lit, bool* return_exp,
                   Range_clause* p_range_clause, Type_switch* p_type_switch)
{
  const Token* token = this->peek_token();

  // An identifier follow by := is a SimpleVarDecl.
  if (token->is_identifier())
    {
      std::string identifier = token->identifier();
      bool is_exported = token->is_identifier_exported();
      source_location location = token->location();

      token = this->advance_token();
      if (token->is_op(OPERATOR_COLONEQ)
          || token->is_op(OPERATOR_COMMA))
        {
          identifier = this->gogo_->pack_hidden_name(identifier, is_exported);
          this->simple_var_decl_or_assignment(identifier, location,
                                              p_range_clause,
                                              (token->is_op(OPERATOR_COLONEQ)
                                               ? p_type_switch
                                               : NULL));
          return NULL;
        }

      this->unget_token(Token::make_identifier_token(identifier, is_exported,
                                                     location));
    }

  Expression* exp = this->expression(PRECEDENCE_NORMAL, true,
                                     may_be_composite_lit,
                                     (p_type_switch == NULL
                                      ? NULL
                                      : &p_type_switch->found));
  if (p_type_switch != NULL && p_type_switch->found)
    {
      p_type_switch->name.clear();
      p_type_switch->location = exp->location();
      p_type_switch->expr = this->verify_not_sink(exp);
      return NULL;
    }
  token = this->peek_token();
  if (token->is_op(OPERATOR_CHANOP))
    {
      this->send_stmt(this->verify_not_sink(exp));
      if (return_exp != NULL)
        *return_exp = true;
    }
  else if (token->is_op(OPERATOR_PLUSPLUS)
           || token->is_op(OPERATOR_MINUSMINUS))
    this->inc_dec_stat(this->verify_not_sink(exp));
  else if (token->is_op(OPERATOR_COMMA)
           || token->is_op(OPERATOR_EQ))
    this->assignment(exp, p_range_clause);
  else if (token->is_op(OPERATOR_PLUSEQ)
           || token->is_op(OPERATOR_MINUSEQ)
           || token->is_op(OPERATOR_OREQ)
           || token->is_op(OPERATOR_XOREQ)
           || token->is_op(OPERATOR_MULTEQ)
           || token->is_op(OPERATOR_DIVEQ)
           || token->is_op(OPERATOR_MODEQ)
           || token->is_op(OPERATOR_LSHIFTEQ)
           || token->is_op(OPERATOR_RSHIFTEQ)
           || token->is_op(OPERATOR_ANDEQ)
           || token->is_op(OPERATOR_BITCLEAREQ))
    this->assignment(this->verify_not_sink(exp), p_range_clause);
  else if (return_exp != NULL)
    return this->verify_not_sink(exp);
  else
    {
      exp = this->verify_not_sink(exp);

      if (token->is_op(OPERATOR_COLONEQ))
        {
          if (!exp->is_error_expression())
            error_at(token->location(), "non-name on left side of %<:=%>");
          while (!token->is_op(OPERATOR_SEMICOLON)
                 && !token->is_eof())
            token = this->advance_token();
          return NULL;
        }

      this->expression_stat(exp);
    }

  return NULL;
}

bool
Parse::simple_stat_may_start_here()
{
  return this->expression_may_start_here();
}

// Parse { Statement ";" } which is used in a few places.  The list of
// statements may end with a right curly brace, in which case the
// semicolon may be omitted.

void
Parse::statement_list()
{
  while (this->statement_may_start_here())
    {
      this->statement(NULL);
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
        this->advance_token();
      else if (this->peek_token()->is_op(OPERATOR_RCURLY))
        break;
      else
        {
          if (!this->peek_token()->is_eof() || !saw_errors())
            error_at(this->location(), "expected %<;%> or %<}%> or newline");
          if (!this->skip_past_error(OPERATOR_RCURLY))
            return;
        }
    }
}

bool
Parse::statement_list_may_start_here()
{
  return this->statement_may_start_here();
}

// ExpressionStat = Expression .

void
Parse::expression_stat(Expression* exp)
{
  this->gogo_->add_statement(Statement::make_statement(exp, false));
}

// SendStmt = Channel "&lt;-" Expression .
// Channel  = Expression .

void
Parse::send_stmt(Expression* channel)
{
  go_assert(this->peek_token()->is_op(OPERATOR_CHANOP));
  source_location loc = this->location();
  this->advance_token();
  Expression* val = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
  Statement* s = Statement::make_send_statement(channel, val, loc);
  this->gogo_->add_statement(s);
}

// IncDecStat = Expression ( "++" | "--" ) .

void
Parse::inc_dec_stat(Expression* exp)
{
  const Token* token = this->peek_token();

  // Lvalue maps require special handling.
  if (exp->index_expression() != NULL)
    exp->index_expression()->set_is_lvalue();

  if (token->is_op(OPERATOR_PLUSPLUS))
    this->gogo_->add_statement(Statement::make_inc_statement(exp));
  else if (token->is_op(OPERATOR_MINUSMINUS))
    this->gogo_->add_statement(Statement::make_dec_statement(exp));
  else
    go_unreachable();
  this->advance_token();
}

// Assignment = ExpressionList assign_op ExpressionList .

// EXP is an expression that we have already parsed.

// If RANGE_CLAUSE is not NULL, then this will recognize a
// RangeClause.

void
Parse::assignment(Expression* expr, Range_clause* p_range_clause)
{
  Expression_list* vars;
  if (!this->peek_token()->is_op(OPERATOR_COMMA))
    {
      vars = new Expression_list();
      vars->push_back(expr);
    }
  else
    {
      this->advance_token();
      vars = this->expression_list(expr, true);
    }

  this->tuple_assignment(vars, p_range_clause);
}

// An assignment statement.  LHS is the list of expressions which
// appear on the left hand side.

// If RANGE_CLAUSE is not NULL, then this will recognize a
// RangeClause.

void
Parse::tuple_assignment(Expression_list* lhs, Range_clause* p_range_clause)
{
  const Token* token = this->peek_token();
  if (!token->is_op(OPERATOR_EQ)
      && !token->is_op(OPERATOR_PLUSEQ)
      && !token->is_op(OPERATOR_MINUSEQ)
      && !token->is_op(OPERATOR_OREQ)
      && !token->is_op(OPERATOR_XOREQ)
      && !token->is_op(OPERATOR_MULTEQ)
      && !token->is_op(OPERATOR_DIVEQ)
      && !token->is_op(OPERATOR_MODEQ)
      && !token->is_op(OPERATOR_LSHIFTEQ)
      && !token->is_op(OPERATOR_RSHIFTEQ)
      && !token->is_op(OPERATOR_ANDEQ)
      && !token->is_op(OPERATOR_BITCLEAREQ))
    {
      error_at(this->location(), "expected assignment operator");
      return;
    }
  Operator op = token->op();
  source_location location = token->location();

  token = this->advance_token();

  if (p_range_clause != NULL && token->is_keyword(KEYWORD_RANGE))
    {
      if (op != OPERATOR_EQ)
        error_at(this->location(), "range clause requires %<=%>");
      this->range_clause_expr(lhs, p_range_clause);
      return;
    }

  Expression_list* vals = this->expression_list(NULL, false);

  // We've parsed everything; check for errors.
  if (lhs == NULL || vals == NULL)
    return;
  for (Expression_list::const_iterator pe = lhs->begin();
       pe != lhs->end();
       ++pe)
    {
      if ((*pe)->is_error_expression())
        return;
      if (op != OPERATOR_EQ && (*pe)->is_sink_expression())
        error_at((*pe)->location(), "cannot use _ as value");
    }
  for (Expression_list::const_iterator pe = vals->begin();
       pe != vals->end();
       ++pe)
    {
      if ((*pe)->is_error_expression())
        return;
    }

  // Map expressions act differently when they are lvalues.
  for (Expression_list::iterator plv = lhs->begin();
       plv != lhs->end();
       ++plv)
    if ((*plv)->index_expression() != NULL)
      (*plv)->index_expression()->set_is_lvalue();

  Call_expression* call;
  Index_expression* map_index;
  Receive_expression* receive;
  Type_guard_expression* type_guard;
  if (lhs->size() == vals->size())
    {
      Statement* s;
      if (lhs->size() > 1)
        {
          if (op != OPERATOR_EQ)
            error_at(location, "multiple values only permitted with %<=%>");
          s = Statement::make_tuple_assignment(lhs, vals, location);
        }
      else
        {
          if (op == OPERATOR_EQ)
            s = Statement::make_assignment(lhs->front(), vals->front(),
                                           location);
          else
            s = Statement::make_assignment_operation(op, lhs->front(),
                                                     vals->front(), location);
          delete lhs;
          delete vals;
        }
      this->gogo_->add_statement(s);
    }
  else if (vals->size() == 1
           && (call = (*vals->begin())->call_expression()) != NULL)
    {
      if (op != OPERATOR_EQ)
        error_at(location, "multiple results only permitted with %<=%>");
      delete vals;
      vals = new Expression_list;
      for (unsigned int i = 0; i < lhs->size(); ++i)
        vals->push_back(Expression::make_call_result(call, i));
      Statement* s = Statement::make_tuple_assignment(lhs, vals, location);
      this->gogo_->add_statement(s);
    }
  else if (lhs->size() == 2
           && vals->size() == 1
           && (map_index = (*vals->begin())->index_expression()) != NULL)
    {
      if (op != OPERATOR_EQ)
        error_at(location, "two values from map requires %<=%>");
      Expression* val = lhs->front();
      Expression* present = lhs->back();
      Statement* s = Statement::make_tuple_map_assignment(val, present,
                                                          map_index, location);
      this->gogo_->add_statement(s);
    }
  else if (lhs->size() == 1
           && vals->size() == 2
           && (map_index = lhs->front()->index_expression()) != NULL)
    {
      if (op != OPERATOR_EQ)
        error_at(location, "assigning tuple to map index requires %<=%>");
      Expression* val = vals->front();
      Expression* should_set = vals->back();
      Statement* s = Statement::make_map_assignment(map_index, val, should_set,
                                                    location);
      this->gogo_->add_statement(s);
    }
  else if (lhs->size() == 2
           && vals->size() == 1
           && (receive = (*vals->begin())->receive_expression()) != NULL)
    {
      if (op != OPERATOR_EQ)
        error_at(location, "two values from receive requires %<=%>");
      Expression* val = lhs->front();
      Expression* success = lhs->back();
      Expression* channel = receive->channel();
      Statement* s = Statement::make_tuple_receive_assignment(val, success,
                                                              channel,
                                                              false,
                                                              location);
      this->gogo_->add_statement(s);
    }
  else if (lhs->size() == 2
           && vals->size() == 1
           && (type_guard = (*vals->begin())->type_guard_expression()) != NULL)
    {
      if (op != OPERATOR_EQ)
        error_at(location, "two values from type guard requires %<=%>");
      Expression* val = lhs->front();
      Expression* ok = lhs->back();
      Expression* expr = type_guard->expr();
      Type* type = type_guard->type();
      Statement* s = Statement::make_tuple_type_guard_assignment(val, ok,
                                                                 expr, type,
                                                                 location);
      this->gogo_->add_statement(s);
    }
  else
    {
      error_at(location, "number of variables does not match number of values");
    }
}

// GoStat = "go" Expression .
// DeferStat = "defer" Expression .

void
Parse::go_or_defer_stat()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_GO)
             || this->peek_token()->is_keyword(KEYWORD_DEFER));
  bool is_go = this->peek_token()->is_keyword(KEYWORD_GO);
  source_location stat_location = this->location();
  this->advance_token();
  source_location expr_location = this->location();
  Expression* expr = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
  Call_expression* call_expr = expr->call_expression();
  if (call_expr == NULL)
    {
      error_at(expr_location, "expected call expression");
      return;
    }

  // Make it easier to simplify go/defer statements by putting every
  // statement in its own block.
  this->gogo_->start_block(stat_location);
  Statement* stat;
  if (is_go)
    stat = Statement::make_go_statement(call_expr, stat_location);
  else
    stat = Statement::make_defer_statement(call_expr, stat_location);
  this->gogo_->add_statement(stat);
  this->gogo_->add_block(this->gogo_->finish_block(stat_location),
                         stat_location);
}

// ReturnStat = "return" [ ExpressionList ] .

void
Parse::return_stat()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_RETURN));
  source_location location = this->location();
  this->advance_token();
  Expression_list* vals = NULL;
  if (this->expression_may_start_here())
    vals = this->expression_list(NULL, false);
  this->gogo_->add_statement(Statement::make_return_statement(vals, location));

  if (vals == NULL
      && this->gogo_->current_function()->func_value()->results_are_named())
    {
      Named_object* function = this->gogo_->current_function();
      Function::Results* results = function->func_value()->result_variables();
      for (Function::Results::const_iterator p = results->begin();
           p != results->end();
           ++p)
        {
          Named_object* no = this->gogo_->lookup((*p)->name(), NULL);
          go_assert(no != NULL);
          if (!no->is_result_variable())
            error_at(location, "%qs is shadowed during return",
                     (*p)->message_name().c_str());
        }
    }
}

// IfStmt = "if" [ SimpleStmt ";" ] Expression Block
//          [ "else" ( IfStmt | Block ) ] .

void
Parse::if_stat()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_IF));
  source_location location = this->location();
  this->advance_token();

  this->gogo_->start_block(location);

  bool saw_simple_stat = false;
  Expression* cond = NULL;
  bool saw_send_stmt;
  if (this->simple_stat_may_start_here())
    {
      cond = this->simple_stat(false, &saw_send_stmt, NULL, NULL);
      saw_simple_stat = true;
    }
  if (cond != NULL && this->peek_token()->is_op(OPERATOR_SEMICOLON))
    {
      // The SimpleStat is an expression statement.
      this->expression_stat(cond);
      cond = NULL;
    }
  if (cond == NULL)
    {
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
        this->advance_token();
      else if (saw_simple_stat)
        {
          if (saw_send_stmt)
            error_at(this->location(),
                     ("send statement used as value; "
                      "use select for non-blocking send"));
          else
            error_at(this->location(),
                     "expected %<;%> after statement in if expression");
          if (!this->expression_may_start_here())
            cond = Expression::make_error(this->location());
        }
      if (cond == NULL && this->peek_token()->is_op(OPERATOR_LCURLY))
        {
          error_at(this->location(),
                   "missing condition in if statement");
          cond = Expression::make_error(this->location());
        }
      if (cond == NULL)
        cond = this->expression(PRECEDENCE_NORMAL, false, false, NULL);
    }

  this->gogo_->start_block(this->location());
  source_location end_loc = this->block();
  Block* then_block = this->gogo_->finish_block(end_loc);

  // Check for the easy error of a newline before "else".
  if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
    {
      source_location semi_loc = this->location();
      if (this->advance_token()->is_keyword(KEYWORD_ELSE))
        error_at(this->location(),
                 "unexpected semicolon or newline before %<else%>");
      else
        this->unget_token(Token::make_operator_token(OPERATOR_SEMICOLON,
                                                     semi_loc));
    }

  Block* else_block = NULL;
  if (this->peek_token()->is_keyword(KEYWORD_ELSE))
    {
      this->gogo_->start_block(this->location());
      const Token* token = this->advance_token();
      if (token->is_keyword(KEYWORD_IF))
        this->if_stat();
      else if (token->is_op(OPERATOR_LCURLY))
        this->block();
      else
        {
          error_at(this->location(), "expected %<if%> or %<{%>");
          this->statement(NULL);
        }
      else_block = this->gogo_->finish_block(this->location());
    }

  this->gogo_->add_statement(Statement::make_if_statement(cond, then_block,
                                                          else_block,
                                                          location));

  this->gogo_->add_block(this->gogo_->finish_block(this->location()),
                         location);
}

// SwitchStmt = ExprSwitchStmt | TypeSwitchStmt .
// ExprSwitchStmt = "switch" [ [ SimpleStat ] ";" ] [ Expression ]
//                      "{" { ExprCaseClause } "}" .
// TypeSwitchStmt  = "switch" [ [ SimpleStat ] ";" ] TypeSwitchGuard
//                      "{" { TypeCaseClause } "}" .
// TypeSwitchGuard = [ identifier ":=" ] Expression "." "(" "type" ")" .

void
Parse::switch_stat(Label* label)
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_SWITCH));
  source_location location = this->location();
  this->advance_token();

  this->gogo_->start_block(location);

  bool saw_simple_stat = false;
  Expression* switch_val = NULL;
  bool saw_send_stmt;
  Type_switch type_switch;
  if (this->simple_stat_may_start_here())
    {
      switch_val = this->simple_stat(false, &saw_send_stmt, NULL,
                                     &type_switch);
      saw_simple_stat = true;
    }
  if (switch_val != NULL && this->peek_token()->is_op(OPERATOR_SEMICOLON))
    {
      // The SimpleStat is an expression statement.
      this->expression_stat(switch_val);
      switch_val = NULL;
    }
  if (switch_val == NULL && !type_switch.found)
    {
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
        this->advance_token();
      else if (saw_simple_stat)
        {
          if (saw_send_stmt)
            error_at(this->location(),
                     ("send statement used as value; "
                      "use select for non-blocking send"));
          else
            error_at(this->location(),
                     "expected %<;%> after statement in switch expression");
        }
      if (!this->peek_token()->is_op(OPERATOR_LCURLY))
        {
          if (this->peek_token()->is_identifier())
            {
              const Token* token = this->peek_token();
              std::string identifier = token->identifier();
              bool is_exported = token->is_identifier_exported();
              source_location id_loc = token->location();

              token = this->advance_token();
              bool is_coloneq = token->is_op(OPERATOR_COLONEQ);
              this->unget_token(Token::make_identifier_token(identifier,
                                                             is_exported,
                                                             id_loc));
              if (is_coloneq)
                {
                  // This must be a TypeSwitchGuard.
                  switch_val = this->simple_stat(false, &saw_send_stmt, NULL,
                                                 &type_switch);
                  if (!type_switch.found)
                    {
                      if (switch_val == NULL
                          || !switch_val->is_error_expression())
                        {
                          error_at(id_loc, "expected type switch assignment");
                          switch_val = Expression::make_error(id_loc);
                        }
                    }
                }
            }
          if (switch_val == NULL && !type_switch.found)
            {
              switch_val = this->expression(PRECEDENCE_NORMAL, false, false,
                                            &type_switch.found);
              if (type_switch.found)
                {
                  type_switch.name.clear();
                  type_switch.expr = switch_val;
                  type_switch.location = switch_val->location();
                }
            }
        }
    }

  if (!this->peek_token()->is_op(OPERATOR_LCURLY))
    {
      source_location token_loc = this->location();
      if (this->peek_token()->is_op(OPERATOR_SEMICOLON)
          && this->advance_token()->is_op(OPERATOR_LCURLY))
        error_at(token_loc, "unexpected semicolon or newline before %<{%>");
      else if (this->peek_token()->is_op(OPERATOR_COLONEQ))
        {
          error_at(token_loc, "invalid variable name");
          this->advance_token();
          this->expression(PRECEDENCE_NORMAL, false, false,
                           &type_switch.found);
          if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
            this->advance_token();
          if (!this->peek_token()->is_op(OPERATOR_LCURLY))
            return;
          if (type_switch.found)
            type_switch.expr = Expression::make_error(location);
        }
      else
        {
          error_at(this->location(), "expected %<{%>");
          this->gogo_->add_block(this->gogo_->finish_block(this->location()),
                                 location);
          return;
        }
    }
  this->advance_token();

  Statement* statement;
  if (type_switch.found)
    statement = this->type_switch_body(label, type_switch, location);
  else
    statement = this->expr_switch_body(label, switch_val, location);

  if (statement != NULL)
    this->gogo_->add_statement(statement);

  this->gogo_->add_block(this->gogo_->finish_block(this->location()),
                         location);
}

// The body of an expression switch.
//   "{" { ExprCaseClause } "}"

Statement*
Parse::expr_switch_body(Label* label, Expression* switch_val,
                        source_location location)
{
  Switch_statement* statement = Statement::make_switch_statement(switch_val,
                                                                 location);

  this->push_break_statement(statement, label);

  Case_clauses* case_clauses = new Case_clauses();
  bool saw_default = false;
  while (!this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      if (this->peek_token()->is_eof())
        {
          if (!saw_errors())
            error_at(this->location(), "missing %<}%>");
          return NULL;
        }
      this->expr_case_clause(case_clauses, &saw_default);
    }
  this->advance_token();

  statement->add_clauses(case_clauses);

  this->pop_break_statement();

  return statement;
}

// ExprCaseClause = ExprSwitchCase ":" [ StatementList ] .
// FallthroughStat = "fallthrough" .

void
Parse::expr_case_clause(Case_clauses* clauses, bool* saw_default)
{
  source_location location = this->location();

  bool is_default = false;
  Expression_list* vals = this->expr_switch_case(&is_default);

  if (!this->peek_token()->is_op(OPERATOR_COLON))
    {
      if (!saw_errors())
        error_at(this->location(), "expected %<:%>");
      return;
    }
  else
    this->advance_token();

  Block* statements = NULL;
  if (this->statement_list_may_start_here())
    {
      this->gogo_->start_block(this->location());
      this->statement_list();
      statements = this->gogo_->finish_block(this->location());
    }

  bool is_fallthrough = false;
  if (this->peek_token()->is_keyword(KEYWORD_FALLTHROUGH))
    {
      is_fallthrough = true;
      if (this->advance_token()->is_op(OPERATOR_SEMICOLON))
        this->advance_token();
    }

  if (is_default)
    {
      if (*saw_default)
        {
          error_at(location, "multiple defaults in switch");
          return;
        }
      *saw_default = true;
    }

  if (is_default || vals != NULL)
    clauses->add(vals, is_default, statements, is_fallthrough, location);
}

// ExprSwitchCase = "case" ExpressionList | "default" .

Expression_list*
Parse::expr_switch_case(bool* is_default)
{
  const Token* token = this->peek_token();
  if (token->is_keyword(KEYWORD_CASE))
    {
      this->advance_token();
      return this->expression_list(NULL, false);
    }
  else if (token->is_keyword(KEYWORD_DEFAULT))
    {
      this->advance_token();
      *is_default = true;
      return NULL;
    }
  else
    {
      if (!saw_errors())
        error_at(this->location(), "expected %<case%> or %<default%>");
      if (!token->is_op(OPERATOR_RCURLY))
        this->advance_token();
      return NULL;
    }
}

// The body of a type switch.
//   "{" { TypeCaseClause } "}" .

Statement*
Parse::type_switch_body(Label* label, const Type_switch& type_switch,
                        source_location location)
{
  Named_object* switch_no = NULL;
  if (!type_switch.name.empty())
    {
      Variable* switch_var = new Variable(NULL, type_switch.expr, false, false,
                                          false, type_switch.location);
      switch_no = this->gogo_->add_variable(type_switch.name, switch_var);
    }

  Type_switch_statement* statement =
    Statement::make_type_switch_statement(switch_no,
                                          (switch_no == NULL
                                           ? type_switch.expr
                                           : NULL),
                                          location);

  this->push_break_statement(statement, label);

  Type_case_clauses* case_clauses = new Type_case_clauses();
  bool saw_default = false;
  while (!this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      if (this->peek_token()->is_eof())
        {
          error_at(this->location(), "missing %<}%>");
          return NULL;
        }
      this->type_case_clause(switch_no, case_clauses, &saw_default);
    }
  this->advance_token();

  statement->add_clauses(case_clauses);

  this->pop_break_statement();

  return statement;
}

// TypeCaseClause  = TypeSwitchCase ":" [ StatementList ] .

void
Parse::type_case_clause(Named_object* switch_no, Type_case_clauses* clauses,
                        bool* saw_default)
{
  source_location location = this->location();

  std::vector<Type*> types;
  bool is_default = false;
  this->type_switch_case(&types, &is_default);

  if (!this->peek_token()->is_op(OPERATOR_COLON))
    error_at(this->location(), "expected %<:%>");
  else
    this->advance_token();

  Block* statements = NULL;
  if (this->statement_list_may_start_here())
    {
      this->gogo_->start_block(this->location());
      if (switch_no != NULL && types.size() == 1)
        {
          Type* type = types.front();
          Expression* init = Expression::make_var_reference(switch_no,
                                                            location);
          init = Expression::make_type_guard(init, type, location);
          Variable* v = new Variable(type, init, false, false, false,
                                     location);
          v->set_is_type_switch_var();
          this->gogo_->add_variable(switch_no->name(), v);
        }
      this->statement_list();
      statements = this->gogo_->finish_block(this->location());
    }

  if (this->peek_token()->is_keyword(KEYWORD_FALLTHROUGH))
    {
      error_at(this->location(),
               "fallthrough is not permitted in a type switch");
      if (this->advance_token()->is_op(OPERATOR_SEMICOLON))
        this->advance_token();
    }

  if (is_default)
    {
      go_assert(types.empty());
      if (*saw_default)
        {
          error_at(location, "multiple defaults in type switch");
          return;
        }
      *saw_default = true;
      clauses->add(NULL, false, true, statements, location);
    }
  else if (!types.empty())
    {
      for (std::vector<Type*>::const_iterator p = types.begin();
           p + 1 != types.end();
           ++p)
        clauses->add(*p, true, false, NULL, location);
      clauses->add(types.back(), false, false, statements, location);
    }
  else
    clauses->add(Type::make_error_type(), false, false, statements, location);
}

// TypeSwitchCase  = "case" type | "default"

// We accept a comma separated list of types.

void
Parse::type_switch_case(std::vector<Type*>* types, bool* is_default)
{
  const Token* token = this->peek_token();
  if (token->is_keyword(KEYWORD_CASE))
    {
      this->advance_token();
      while (true)
        {
          Type* t = this->type();

          if (!t->is_error_type())
            types->push_back(t);
          else
            {
              token = this->peek_token();
              while (!token->is_op(OPERATOR_COLON)
                     && !token->is_op(OPERATOR_COMMA)
                     && !token->is_op(OPERATOR_RCURLY)
                     && !token->is_eof())
                token = this->advance_token();
            }

          if (!this->peek_token()->is_op(OPERATOR_COMMA))
            break;
          this->advance_token();
        }
    }
  else if (token->is_keyword(KEYWORD_DEFAULT))
    {
      this->advance_token();
      *is_default = true;
    }
  else
    {
      error_at(this->location(), "expected %<case%> or %<default%>");
      if (!token->is_op(OPERATOR_RCURLY))
        this->advance_token();
    }
}

// SelectStat = "select" "{" { CommClause } "}" .

void
Parse::select_stat(Label* label)
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_SELECT));
  source_location location = this->location();
  const Token* token = this->advance_token();

  if (!token->is_op(OPERATOR_LCURLY))
    {
      source_location token_loc = token->location();
      if (token->is_op(OPERATOR_SEMICOLON)
          && this->advance_token()->is_op(OPERATOR_LCURLY))
        error_at(token_loc, "unexpected semicolon or newline before %<{%>");
      else
        {
          error_at(this->location(), "expected %<{%>");
          return;
        }
    }
  this->advance_token();

  Select_statement* statement = Statement::make_select_statement(location);

  this->push_break_statement(statement, label);

  Select_clauses* select_clauses = new Select_clauses();
  bool saw_default = false;
  while (!this->peek_token()->is_op(OPERATOR_RCURLY))
    {
      if (this->peek_token()->is_eof())
        {
          error_at(this->location(), "expected %<}%>");
          return;
        }
      this->comm_clause(select_clauses, &saw_default);
    }

  this->advance_token();

  statement->add_clauses(select_clauses);

  this->pop_break_statement();

  this->gogo_->add_statement(statement);
}

// CommClause = CommCase ":" { Statement ";" } .

void
Parse::comm_clause(Select_clauses* clauses, bool* saw_default)
{
  source_location location = this->location();
  bool is_send = false;
  Expression* channel = NULL;
  Expression* val = NULL;
  Expression* closed = NULL;
  std::string varname;
  std::string closedname;
  bool is_default = false;
  bool got_case = this->comm_case(&is_send, &channel, &val, &closed,
                                  &varname, &closedname, &is_default);

  if (!is_send
      && varname.empty()
      && closedname.empty()
      && val != NULL
      && val->index_expression() != NULL)
    val->index_expression()->set_is_lvalue();

  if (this->peek_token()->is_op(OPERATOR_COLON))
    this->advance_token();
  else
    error_at(this->location(), "expected colon");

  this->gogo_->start_block(this->location());

  Named_object* var = NULL;
  if (!varname.empty())
    {
      // FIXME: LOCATION is slightly wrong here.
      Variable* v = new Variable(NULL, channel, false, false, false,
                                 location);
      v->set_type_from_chan_element();
      var = this->gogo_->add_variable(varname, v);
    }

  Named_object* closedvar = NULL;
  if (!closedname.empty())
    {
      // FIXME: LOCATION is slightly wrong here.
      Variable* v = new Variable(Type::lookup_bool_type(), NULL,
                                 false, false, false, location);
      closedvar = this->gogo_->add_variable(closedname, v);
    }

  this->statement_list();

  Block* statements = this->gogo_->finish_block(this->location());

  if (is_default)
    {
      if (*saw_default)
        {
          error_at(location, "multiple defaults in select");
          return;
        }
      *saw_default = true;
    }

  if (got_case)
    clauses->add(is_send, channel, val, closed, var, closedvar, is_default,
                 statements, location);
  else if (statements != NULL)
    {
      // Add the statements to make sure that any names they define
      // are traversed.
      this->gogo_->add_block(statements, location);
    }
}

// CommCase   = "case" ( SendStmt | RecvStmt ) | "default" .

bool
Parse::comm_case(bool* is_send, Expression** channel, Expression** val,
                 Expression** closed, std::string* varname,
                 std::string* closedname, bool* is_default)
{
  const Token* token = this->peek_token();
  if (token->is_keyword(KEYWORD_DEFAULT))
    {
      this->advance_token();
      *is_default = true;
    }
  else if (token->is_keyword(KEYWORD_CASE))
    {
      this->advance_token();
      if (!this->send_or_recv_stmt(is_send, channel, val, closed, varname,
                                   closedname))
        return false;
    }
  else
    {
      error_at(this->location(), "expected %<case%> or %<default%>");
      if (!token->is_op(OPERATOR_RCURLY))
        this->advance_token();
      return false;
    }

  return true;
}

// RecvStmt   = [ Expression [ "," Expression ] ( "=" | ":=" ) ] RecvExpr .
// RecvExpr   = Expression .

bool
Parse::send_or_recv_stmt(bool* is_send, Expression** channel, Expression** val,
                         Expression** closed, std::string* varname,
                         std::string* closedname)
{
  const Token* token = this->peek_token();
  bool saw_comma = false;
  bool closed_is_id = false;
  if (token->is_identifier())
    {
      Gogo* gogo = this->gogo_;
      std::string recv_var = token->identifier();
      bool is_rv_exported = token->is_identifier_exported();
      source_location recv_var_loc = token->location();
      token = this->advance_token();
      if (token->is_op(OPERATOR_COLONEQ))
        {
          // case rv := <-c:
          if (!this->advance_token()->is_op(OPERATOR_CHANOP))
            {
              error_at(this->location(), "expected %<<-%>");
              return false;
            }
          if (recv_var == "_")
            {
              error_at(recv_var_loc,
                       "no new variables on left side of %<:=%>");
              recv_var = "blank";
            }
          *is_send = false;
          *varname = gogo->pack_hidden_name(recv_var, is_rv_exported);
          this->advance_token();
          *channel = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
          return true;
        }
      else if (token->is_op(OPERATOR_COMMA))
        {
          token = this->advance_token();
          if (token->is_identifier())
            {
              std::string recv_closed = token->identifier();
              bool is_rc_exported = token->is_identifier_exported();
              source_location recv_closed_loc = token->location();
              closed_is_id = true;

              token = this->advance_token();
              if (token->is_op(OPERATOR_COLONEQ))
                {
                  // case rv, rc := <-c:
                  if (!this->advance_token()->is_op(OPERATOR_CHANOP))
                    {
                      error_at(this->location(), "expected %<<-%>");
                      return false;
                    }
                  if (recv_var == "_" && recv_closed == "_")
                    {
                      error_at(recv_var_loc,
                               "no new variables on left side of %<:=%>");
                      recv_var = "blank";
                    }
                  *is_send = false;
                  if (recv_var != "_")
                    *varname = gogo->pack_hidden_name(recv_var,
                                                      is_rv_exported);
                  if (recv_closed != "_")
                    *closedname = gogo->pack_hidden_name(recv_closed,
                                                         is_rc_exported);
                  this->advance_token();
                  *channel = this->expression(PRECEDENCE_NORMAL, false, true,
                                              NULL);
                  return true;
                }

              this->unget_token(Token::make_identifier_token(recv_closed,
                                                             is_rc_exported,
                                                             recv_closed_loc));
            }

          *val = this->id_to_expression(gogo->pack_hidden_name(recv_var,
                                                               is_rv_exported),
                                        recv_var_loc);
          saw_comma = true;
        }
      else
        this->unget_token(Token::make_identifier_token(recv_var,
                                                       is_rv_exported,
                                                       recv_var_loc));
    }

  // If SAW_COMMA is false, then we are looking at the start of the
  // send or receive expression.  If SAW_COMMA is true, then *VAL is
  // set and we just read a comma.

  Expression* e;
  if (saw_comma || !this->peek_token()->is_op(OPERATOR_CHANOP))
    e = this->expression(PRECEDENCE_NORMAL, true, true, NULL);
  else
    {
      // case <-c:
      *is_send = false;
      this->advance_token();
      *channel = this->expression(PRECEDENCE_NORMAL, false, true, NULL);

      // The next token should be ':'.  If it is '<-', then we have
      // case <-c <- v:
      // which is to say, send on a channel received from a channel.
      if (!this->peek_token()->is_op(OPERATOR_CHANOP))
        return true;

      e = Expression::make_receive(*channel, (*channel)->location());
    }

  if (this->peek_token()->is_op(OPERATOR_EQ))
    {
      if (!this->advance_token()->is_op(OPERATOR_CHANOP))
        {
          error_at(this->location(), "missing %<<-%>");
          return false;
        }
      *is_send = false;
      this->advance_token();
      *channel = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
      if (saw_comma)
        {
          // case v, e = <-c:
          // *VAL is already set.
          if (!e->is_sink_expression())
            *closed = e;
        }
      else
        {
          // case v = <-c:
          if (!e->is_sink_expression())
            *val = e;
        }
      return true;
    }

  if (saw_comma)
    {
      if (closed_is_id)
        error_at(this->location(), "expected %<=%> or %<:=%>");
      else
        error_at(this->location(), "expected %<=%>");
      return false;
    }

  if (this->peek_token()->is_op(OPERATOR_CHANOP))
    {
      // case c <- v:
      *is_send = true;
      *channel = this->verify_not_sink(e);
      this->advance_token();
      *val = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
      return true;
    }

  error_at(this->location(), "expected %<<-%> or %<=%>");
  return false;
}

// ForStat = "for" [ Condition | ForClause | RangeClause ] Block .
// Condition = Expression .

void
Parse::for_stat(Label* label)
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_FOR));
  source_location location = this->location();
  const Token* token = this->advance_token();

  // Open a block to hold any variables defined in the init statement
  // of the for statement.
  this->gogo_->start_block(location);

  Block* init = NULL;
  Expression* cond = NULL;
  Block* post = NULL;
  Range_clause range_clause;

  if (!token->is_op(OPERATOR_LCURLY))
    {
      if (token->is_keyword(KEYWORD_VAR))
        {
          error_at(this->location(),
                   "var declaration not allowed in for initializer");
          this->var_decl();
        }

      if (token->is_op(OPERATOR_SEMICOLON))
        this->for_clause(&cond, &post);
      else
        {
          // We might be looking at a Condition, an InitStat, or a
          // RangeClause.
          bool saw_send_stmt;
          cond = this->simple_stat(false, &saw_send_stmt, &range_clause, NULL);
          if (!this->peek_token()->is_op(OPERATOR_SEMICOLON))
            {
              if (cond == NULL && !range_clause.found)
                {
                  if (saw_send_stmt)
                    error_at(this->location(),
                             ("send statement used as value; "
                              "use select for non-blocking send"));
                  else
                    error_at(this->location(), "parse error in for statement");
                }
            }
          else
            {
              if (range_clause.found)
                error_at(this->location(), "parse error after range clause");

              if (cond != NULL)
                {
                  // COND is actually an expression statement for
                  // InitStat at the start of a ForClause.
                  this->expression_stat(cond);
                  cond = NULL;
                }

              this->for_clause(&cond, &post);
            }
        }
    }

  // Build the For_statement and note that it is the current target
  // for break and continue statements.

  For_statement* sfor;
  For_range_statement* srange;
  Statement* s;
  if (!range_clause.found)
    {
      sfor = Statement::make_for_statement(init, cond, post, location);
      s = sfor;
      srange = NULL;
    }
  else
    {
      srange = Statement::make_for_range_statement(range_clause.index,
                                                   range_clause.value,
                                                   range_clause.range,
                                                   location);
      s = srange;
      sfor = NULL;
    }

  this->push_break_statement(s, label);
  this->push_continue_statement(s, label);

  // Gather the block of statements in the loop and add them to the
  // For_statement.

  this->gogo_->start_block(this->location());
  source_location end_loc = this->block();
  Block* statements = this->gogo_->finish_block(end_loc);

  if (sfor != NULL)
    sfor->add_statements(statements);
  else
    srange->add_statements(statements);

  // This is no longer the break/continue target.
  this->pop_break_statement();
  this->pop_continue_statement();

  // Add the For_statement to the list of statements, and close out
  // the block we started to hold any variables defined in the for
  // statement.

  this->gogo_->add_statement(s);

  this->gogo_->add_block(this->gogo_->finish_block(this->location()),
                         location);
}

// ForClause = [ InitStat ] ";" [ Condition ] ";" [ PostStat ] .
// InitStat = SimpleStat .
// PostStat = SimpleStat .

// We have already read InitStat at this point.

void
Parse::for_clause(Expression** cond, Block** post)
{
  go_assert(this->peek_token()->is_op(OPERATOR_SEMICOLON));
  this->advance_token();
  if (this->peek_token()->is_op(OPERATOR_SEMICOLON))
    *cond = NULL;
  else if (this->peek_token()->is_op(OPERATOR_LCURLY))
    {
      error_at(this->location(),
               "unexpected semicolon or newline before %<{%>");
      *cond = NULL;
      *post = NULL;
      return;
    }
  else
    *cond = this->expression(PRECEDENCE_NORMAL, false, true, NULL);
  if (!this->peek_token()->is_op(OPERATOR_SEMICOLON))
    error_at(this->location(), "expected semicolon");
  else
    this->advance_token();

  if (this->peek_token()->is_op(OPERATOR_LCURLY))
    *post = NULL;
  else
    {
      this->gogo_->start_block(this->location());
      this->simple_stat(false, NULL, NULL, NULL);
      *post = this->gogo_->finish_block(this->location());
    }
}

// RangeClause = IdentifierList ( "=" | ":=" ) "range" Expression .

// This is the := version.  It is called with a list of identifiers.

void
Parse::range_clause_decl(const Typed_identifier_list* til,
                         Range_clause* p_range_clause)
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_RANGE));
  source_location location = this->location();

  p_range_clause->found = true;

  go_assert(til->size() >= 1);
  if (til->size() > 2)
    error_at(this->location(), "too many variables for range clause");

  this->advance_token();
  Expression* expr = this->expression(PRECEDENCE_NORMAL, false, false, NULL);
  p_range_clause->range = expr;

  bool any_new = false;

  const Typed_identifier* pti = &til->front();
  Named_object* no = this->init_var(*pti, NULL, expr, true, true, &any_new);
  if (any_new && no->is_variable())
    no->var_value()->set_type_from_range_index();
  p_range_clause->index = Expression::make_var_reference(no, location);

  if (til->size() == 1)
    p_range_clause->value = NULL;
  else
    {
      pti = &til->back();
      bool is_new = false;
      no = this->init_var(*pti, NULL, expr, true, true, &is_new);
      if (is_new && no->is_variable())
        no->var_value()->set_type_from_range_value();
      if (is_new)
        any_new = true;
      p_range_clause->value = Expression::make_var_reference(no, location);
    }

  if (!any_new)
    error_at(location, "variables redeclared but no variable is new");
}

// The = version of RangeClause.  This is called with a list of
// expressions.

void
Parse::range_clause_expr(const Expression_list* vals,
                         Range_clause* p_range_clause)
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_RANGE));

  p_range_clause->found = true;

  go_assert(vals->size() >= 1);
  if (vals->size() > 2)
    error_at(this->location(), "too many variables for range clause");

  this->advance_token();
  p_range_clause->range = this->expression(PRECEDENCE_NORMAL, false, false,
                                           NULL);

  p_range_clause->index = vals->front();
  if (vals->size() == 1)
    p_range_clause->value = NULL;
  else
    p_range_clause->value = vals->back();
}

// Push a statement on the break stack.

void
Parse::push_break_statement(Statement* enclosing, Label* label)
{
  if (this->break_stack_ == NULL)
    this->break_stack_ = new Bc_stack();
  this->break_stack_->push_back(std::make_pair(enclosing, label));
}

// Push a statement on the continue stack.

void
Parse::push_continue_statement(Statement* enclosing, Label* label)
{
  if (this->continue_stack_ == NULL)
    this->continue_stack_ = new Bc_stack();
  this->continue_stack_->push_back(std::make_pair(enclosing, label));
}

// Pop the break stack.

void
Parse::pop_break_statement()
{
  this->break_stack_->pop_back();
}

// Pop the continue stack.

void
Parse::pop_continue_statement()
{
  this->continue_stack_->pop_back();
}

// Find a break or continue statement given a label name.

Statement*
Parse::find_bc_statement(const Bc_stack* bc_stack, const std::string& label)
{
  if (bc_stack == NULL)
    return NULL;
  for (Bc_stack::const_reverse_iterator p = bc_stack->rbegin();
       p != bc_stack->rend();
       ++p)
    {
      if (p->second != NULL && p->second->name() == label)
        {
          p->second->set_is_used();
          return p->first;
        }
    }
  return NULL;
}

// BreakStat = "break" [ identifier ] .

void
Parse::break_stat()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_BREAK));
  source_location location = this->location();

  const Token* token = this->advance_token();
  Statement* enclosing;
  if (!token->is_identifier())
    {
      if (this->break_stack_ == NULL || this->break_stack_->empty())
        {
          error_at(this->location(),
                   "break statement not within for or switch or select");
          return;
        }
      enclosing = this->break_stack_->back().first;
    }
  else
    {
      enclosing = this->find_bc_statement(this->break_stack_,
                                          token->identifier());
      if (enclosing == NULL)
        {
          // If there is a label with this name, mark it as used to
          // avoid a useless error about an unused label.
          this->gogo_->add_label_reference(token->identifier(), 0, false);

          error_at(token->location(), "invalid break label %qs",
                   Gogo::message_name(token->identifier()).c_str());
          this->advance_token();
          return;
        }
      this->advance_token();
    }

  Unnamed_label* label;
  if (enclosing->classification() == Statement::STATEMENT_FOR)
    label = enclosing->for_statement()->break_label();
  else if (enclosing->classification() == Statement::STATEMENT_FOR_RANGE)
    label = enclosing->for_range_statement()->break_label();
  else if (enclosing->classification() == Statement::STATEMENT_SWITCH)
    label = enclosing->switch_statement()->break_label();
  else if (enclosing->classification() == Statement::STATEMENT_TYPE_SWITCH)
    label = enclosing->type_switch_statement()->break_label();
  else if (enclosing->classification() == Statement::STATEMENT_SELECT)
    label = enclosing->select_statement()->break_label();
  else
    go_unreachable();

  this->gogo_->add_statement(Statement::make_break_statement(label,
                                                             location));
}

// ContinueStat = "continue" [ identifier ] .

void
Parse::continue_stat()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_CONTINUE));
  source_location location = this->location();

  const Token* token = this->advance_token();
  Statement* enclosing;
  if (!token->is_identifier())
    {
      if (this->continue_stack_ == NULL || this->continue_stack_->empty())
        {
          error_at(this->location(), "continue statement not within for");
          return;
        }
      enclosing = this->continue_stack_->back().first;
    }
  else
    {
      enclosing = this->find_bc_statement(this->continue_stack_,
                                          token->identifier());
      if (enclosing == NULL)
        {
          // If there is a label with this name, mark it as used to
          // avoid a useless error about an unused label.
          this->gogo_->add_label_reference(token->identifier(), 0, false);

          error_at(token->location(), "invalid continue label %qs",
                   Gogo::message_name(token->identifier()).c_str());
          this->advance_token();
          return;
        }
      this->advance_token();
    }

  Unnamed_label* label;
  if (enclosing->classification() == Statement::STATEMENT_FOR)
    label = enclosing->for_statement()->continue_label();
  else if (enclosing->classification() == Statement::STATEMENT_FOR_RANGE)
    label = enclosing->for_range_statement()->continue_label();
  else
    go_unreachable();

  this->gogo_->add_statement(Statement::make_continue_statement(label,
                                                                location));
}

// GotoStat = "goto" identifier .

void
Parse::goto_stat()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_GOTO));
  source_location location = this->location();
  const Token* token = this->advance_token();
  if (!token->is_identifier())
    error_at(this->location(), "expected label for goto");
  else
    {
      Label* label = this->gogo_->add_label_reference(token->identifier(),
                                                      location, true);
      Statement* s = Statement::make_goto_statement(label, location);
      this->gogo_->add_statement(s);
      this->advance_token();
    }
}

// PackageClause = "package" PackageName .

void
Parse::package_clause()
{
  const Token* token = this->peek_token();
  source_location location = token->location();
  std::string name;
  if (!token->is_keyword(KEYWORD_PACKAGE))
    {
      error_at(this->location(), "program must start with package clause");
      name = "ERROR";
    }
  else
    {
      token = this->advance_token();
      if (token->is_identifier())
        {
          name = token->identifier();
          if (name == "_")
            {
              error_at(this->location(), "invalid package name _");
              name = "blank";
            }
          this->advance_token();
        }
      else
        {
          error_at(this->location(), "package name must be an identifier");
          name = "ERROR";
        }
    }
  this->gogo_->set_package_name(name, location);
}

// ImportDecl = "import" Decl<ImportSpec> .

void
Parse::import_decl()
{
  go_assert(this->peek_token()->is_keyword(KEYWORD_IMPORT));
  this->advance_token();
  this->decl(&Parse::import_spec, NULL);
}

// ImportSpec = [ "." | PackageName ] PackageFileName .

void
Parse::import_spec(void*)
{
  const Token* token = this->peek_token();
  source_location location = token->location();

  std::string local_name;
  bool is_local_name_exported = false;
  if (token->is_op(OPERATOR_DOT))
    {
      local_name = ".";
      token = this->advance_token();
    }
  else if (token->is_identifier())
    {
      local_name = token->identifier();
      is_local_name_exported = token->is_identifier_exported();
      token = this->advance_token();
    }

  if (!token->is_string())
    {
      error_at(this->location(), "missing import package name");
      return;
    }

  this->gogo_->import_package(token->string_value(), local_name,
                              is_local_name_exported, location);

  this->advance_token();
}

// SourceFile       = PackageClause ";" { ImportDecl ";" }
//                      { TopLevelDecl ";" } .

void
Parse::program()
{
  this->package_clause();

  const Token* token = this->peek_token();
  if (token->is_op(OPERATOR_SEMICOLON))
    token = this->advance_token();
  else
    error_at(this->location(),
             "expected %<;%> or newline after package clause");

  while (token->is_keyword(KEYWORD_IMPORT))
    {
      this->import_decl();
      token = this->peek_token();
      if (token->is_op(OPERATOR_SEMICOLON))
        token = this->advance_token();
      else
        error_at(this->location(),
                 "expected %<;%> or newline after import declaration");
    }

  while (!token->is_eof())
    {
      if (this->declaration_may_start_here())
        this->declaration();
      else
        {
          error_at(this->location(), "expected declaration");
          do
            this->advance_token();
          while (!this->peek_token()->is_eof()
                 && !this->peek_token()->is_op(OPERATOR_SEMICOLON)
                 && !this->peek_token()->is_op(OPERATOR_RCURLY));
          if (!this->peek_token()->is_eof()
              && !this->peek_token()->is_op(OPERATOR_SEMICOLON))
            this->advance_token();
        }
      token = this->peek_token();
      if (token->is_op(OPERATOR_SEMICOLON))
        token = this->advance_token();
      else if (!token->is_eof() || !saw_errors())
        {
          if (token->is_op(OPERATOR_CHANOP))
            error_at(this->location(),
                     ("send statement used as value; "
                      "use select for non-blocking send"));
          else
            error_at(this->location(),
                     "expected %<;%> or newline after top level declaration");
          this->skip_past_error(OPERATOR_INVALID);
        }
    }
}

// Reset the current iota value.

void
Parse::reset_iota()
{
  this->iota_ = 0;
}

// Return the current iota value.

int
Parse::iota_value()
{
  return this->iota_;
}

// Increment the current iota value.

void
Parse::increment_iota()
{
  ++this->iota_;
}

// Skip forward to a semicolon or OP.  OP will normally be
// OPERATOR_RPAREN or OPERATOR_RCURLY.  If we find a semicolon, move
// past it and return.  If we find OP, it will be the next token to
// read.  Return true if we are OK, false if we found EOF.

bool
Parse::skip_past_error(Operator op)
{
  const Token* token = this->peek_token();
  while (!token->is_op(op))
    {
      if (token->is_eof())
        return false;
      if (token->is_op(OPERATOR_SEMICOLON))
        {
          this->advance_token();
          return true;
        }
      token = this->advance_token();
    }
  return true;
}

// Check that an expression is not a sink.

Expression*
Parse::verify_not_sink(Expression* expr)
{
  if (expr->is_sink_expression())
    {
      error_at(expr->location(), "cannot use _ as value");
      expr = Expression::make_error(expr->location());
    }
  return expr;
}