text: #include <cstdlib>
  #include <iostream>
  #include "parser.hpp"
  #include "file.hpp"
  #include "inspect.hpp"
  #include "to_string.hpp"
  #include "constants.hpp"
  
  #ifndef SASS_PRELEXER
  #include "prelexer.hpp"
  #endif
  
  namespace Sass {
    using namespace std;
    using namespace Constants;
  
    Parser Parser::from_c_str(const char* str, Context& ctx, string path, size_t line)
    {
      Parser p(ctx, path, line);
      p.source   = str;
      p.position = p.source;
      p.end      = str + strlen(str);
      return p;
    }
  
    Parser Parser::from_token(Token t, Context& ctx, string path, size_t line)
    {
      Parser p(ctx, path, line);
      p.source   = t.begin;
      p.position = p.source;
      p.end      = t.end;
      return p;
    }
  
    Block* Parser::parse()
    {
      Block* root = new (ctx.mem) Block(path, line);
      root->is_root(true);
      read_bom();
      lex< optional_spaces >();
      Selector_Lookahead lookahead_result;
      while (position < end) {
        if (lex< block_comment >()) {
          String_Constant* contents = new (ctx.mem) String_Constant(path, line, lexed);
          Comment*     comment  = new (ctx.mem) Comment(path, line, contents);
          (*root) << comment;
        }
        else if (peek< import >()) {
          Import* imp = parse_import();
          (*root) << imp;
          if (!imp->files().empty()) {
            for (size_t i = 0, S = imp->files().size(); i < S; ++i) {
              (*root) << new (ctx.mem) Import_Stub(path, line, imp->files()[i]);
            }
          }
          if (!lex< exactly<';'> >()) error("top-level @import directive must be terminated by ';'");
        }
        else if (peek< mixin >() || peek< function >()) {
          (*root) << parse_definition();
        }
        else if (peek< variable >()) {
          (*root) << parse_assignment();
          if (!lex< exactly<';'> >()) error("top-level variable binding must be terminated by ';'");
        }
        else if (peek< sequence< optional< exactly<'*'> >, alternatives< identifier_schema, identifier >, optional_spaces, exactly<':'>, optional_spaces, exactly<'{'> > >(position)) {
          (*root) << parse_propset();
        }
        else if (peek< include >() /* || peek< exactly<'+'> >() */) {
          Mixin_Call* mixin_call = parse_mixin_call();
          (*root) << mixin_call;
          if (!mixin_call->block() && !lex< exactly<';'> >()) error("top-level @include directive must be terminated by ';'");
        }
        else if (peek< if_directive >()) {
          (*root) << parse_if_directive();
        }
        else if (peek< for_directive >()) {
          (*root) << parse_for_directive();
        }
        else if (peek< each_directive >()) {
          (*root) << parse_each_directive();
        }
        else if (peek< while_directive >()) {
          (*root) << parse_while_directive();
        }
        else if (peek< media >()) {
          (*root) << parse_media_block();
        }
        else if (peek< warn >()) {
          (*root) << parse_warning();
          if (!lex< exactly<';'> >()) error("top-level @warn directive must be terminated by ';'");
        }
        // ignore the @charset directive for now
        else if (lex< exactly< charset_kwd > >()) {
          lex< string_constant >();
          lex< exactly<';'> >();
        }
        else if (peek< at_keyword >()) {
          At_Rule* at_rule = parse_at_rule();
          (*root) << at_rule;
          if (!at_rule->block() && !lex< exactly<';'> >()) error("top-level directive must be terminated by ';'");
        }
        else if ((lookahead_result = lookahead_for_selector(position)).found) {
          (*root) << parse_ruleset(lookahead_result);
        }
        else {
          lex< spaces_and_comments >();
          if (position >= end) break;
          error("invalid top-level expression");
        }
        lex< optional_spaces >();
      }
      return root;
    }
  
    Import* Parser::parse_import()
    {
      lex< import >();
      Import* imp = new (ctx.mem) Import(path, line);
      bool first = true;
      do {
        if (lex< string_constant >()) {
          string import_path(lexed);
          size_t dot = import_path.find_last_of('.');
          if (dot != string::npos && import_path.substr(dot, 4) == ".css") {
            String_Constant* loc = new (ctx.mem) String_Constant(path, line, import_path);
            Argument* loc_arg = new (ctx.mem) Argument(path, line, loc);
            Arguments* loc_args = new (ctx.mem) Arguments(path, line);
            (*loc_args) << loc_arg;
            Function_Call* new_url = new (ctx.mem) Function_Call(path, line, "url", loc_args);
            imp->urls().push_back(new_url);
          }
          else {
            string current_dir = File::dir_name(path);
            string resolved(ctx.add_file(File::join_paths(current_dir, unquote(import_path))));
            if (resolved.empty()) error("file to import not found or unreadable: " + import_path);
            imp->files().push_back(resolved);
          }
        }
        else if (peek< uri_prefix >()) {
          imp->urls().push_back(parse_function_call());
        }
        else {
          if (first) error("@import directive requires a url or quoted path");
          else error("expecting another url or quoted path in @import list");
        }
        first = false;
      } while (lex< exactly<','> >());
      return imp;
    }
  
    Definition* Parser::parse_definition()
    {
      Definition::Type which_type = Definition::MIXIN;
      if      (lex< mixin >())    which_type = Definition::MIXIN;
      else if (lex< function >()) which_type = Definition::FUNCTION;
      string which_str(lexed);
      if (!lex< identifier >()) error("invalid name in " + which_str + " definition");
      string name(lexed);
      size_t line_of_def = line;
      Parameters* params = parse_parameters();
      if (!peek< exactly<'{'> >()) error("body for " + which_str + " " + name + " must begin with a '{'");
      if (which_type == Definition::MIXIN) stack.push_back(mixin_def);
      else stack.push_back(function_def);
      Block* body = parse_block();
      stack.pop_back();
      Definition* def = new (ctx.mem) Definition(path, line_of_def, name, params, body, which_type);
      return def;
    }
  
    Parameters* Parser::parse_parameters()
    {
      string name(lexed); // for the error message
      Parameters* params = new (ctx.mem) Parameters(path, line);
      if (lex< exactly<'('> >()) {
        // if there's anything there at all
        if (!peek< exactly<')'> >()) {
          do (*params) << parse_parameter();
          while (lex< exactly<','> >());
        }
        if (!lex< exactly<')'> >()) error("expected a variable name (e.g. $x) or ')' for the parameter list for " + name);
      }
      return params;
    }
  
    Parameter* Parser::parse_parameter()
    {
      lex< variable >();
      string name(lexed);
      Expression* val = 0;
      bool is_rest = false;
      if (lex< exactly<':'> >()) { // there's a default value
        val = parse_space_list();
        val->is_delayed(false);
      }
      else if (lex< exactly< ellipsis > >()) {
        is_rest = true;
      }
      Parameter* p = new (ctx.mem) Parameter(path, line, name, val, is_rest);
      return p;
    }
  
    Mixin_Call* Parser::parse_mixin_call()
    {
      lex< include >() /* || lex< exactly<'+'> >() */;
      if (!lex< identifier >()) error("invalid name in @include directive");
      size_t line_of_call = line;
      string name(lexed);
      Arguments* args = parse_arguments();
      Block* content = 0;
      if (peek< exactly<'{'> >()) {
        content = parse_block();
      }
      Mixin_Call* the_call = new (ctx.mem) Mixin_Call(path, line_of_call, name, args, content);
      return the_call;
    }
  
    Arguments* Parser::parse_arguments()
    {
      string name(lexed);
      Arguments* args = new (ctx.mem) Arguments(path, line);
  
      if (lex< exactly<'('> >()) {
        // if there's anything there at all
        if (!peek< exactly<')'> >()) {
          do (*args) << parse_argument();
          while (lex< exactly<','> >());
        }
        if (!lex< exactly<')'> >()) error("expected a variable name (e.g. $x) or ')' for the parameter list for " + name);
      }
  
      return args;
    }
  
    Argument* Parser::parse_argument()
    {
      Argument* arg;
      if (peek< sequence < variable, spaces_and_comments, exactly<':'> > >()) {
        lex< variable >();
        string name(lexed);
        lex< exactly<':'> >();
        Expression* val = parse_space_list();
        val->is_delayed(false);
        arg = new (ctx.mem) Argument(path, line, val, name);
      }
      else {
        bool is_arglist = false;
        Expression* val = parse_space_list();
        val->is_delayed(false);
        if (lex< exactly< ellipsis > >()) {
          is_arglist = true;
        }
        arg = new (ctx.mem) Argument(path, line, val, "", is_arglist);
      }
      return arg;
    }
  
    Assignment* Parser::parse_assignment()
    {
      lex< variable >();
      string name(lexed);
      size_t var_line = line;
      if (!lex< exactly<':'> >()) error("expected ':' after " + name + " in assignment statement");
      Expression* val = parse_list();
      val->is_delayed(false);
      bool is_guarded = lex< default_flag >();
      Assignment* var = new (ctx.mem) Assignment(path, var_line, name, val, is_guarded);
      return var;
    }
  
    Propset* Parser::parse_propset()
    {
      String* property_segment;
      if (peek< sequence< optional< exactly<'*'> >, identifier_schema > >()) {
        property_segment = parse_identifier_schema();
      }
      else {
        lex< sequence< optional< exactly<'*'> >, identifier > >();
        property_segment = new (ctx.mem) String_Constant(path, line, lexed);
      }
      Propset* propset = new (ctx.mem) Propset(path, line, property_segment);
      lex< exactly<':'> >();
  
      if (!peek< exactly<'{'> >()) error("expected a '{' after namespaced property");
  
      propset->block(parse_block());
  
      return propset;
    }
  
    Ruleset* Parser::parse_ruleset(Selector_Lookahead lookahead)
    {
      Selector* sel;
      if (lookahead.has_interpolants) {
        sel = parse_selector_schema(lookahead.found);
      }
      else {
        sel = parse_selector_group();
      }
      if (!peek< exactly<'{'> >()) error("expected a '{' after the selector");
      Block* block = parse_block();
      Ruleset* ruleset = new (ctx.mem) Ruleset(path, line, sel, block);
      return ruleset;
    }
  
    Selector_Schema* Parser::parse_selector_schema(const char* end_of_selector)
    {
      const char* i = position;
      const char* p;
      String_Schema* schema = new (ctx.mem) String_Schema(path, line);
  
      while (i < end_of_selector) {
        p = find_first_in_interval< exactly<hash_lbrace> >(i, end_of_selector);
        if (p) {
          // accumulate the preceding segment if there is one
          if (i < p) (*schema) << new (ctx.mem) String_Constant(path, line, Token(i, p));
          // find the end of the interpolant and parse it
          const char* j = find_first_in_interval< exactly<rbrace> >(p, end_of_selector);
          Expression* interp_node = Parser::from_token(Token(p+2, j), ctx, path, line).parse_list();
          interp_node->is_interpolant(true);
          (*schema) << interp_node;
          i = j + 1;
        }
        else { // no interpolants left; add the last segment if there is one
          if (i < end_of_selector) (*schema) << new (ctx.mem) String_Constant(path, line, Token(i, end_of_selector));
          break;
        }
      }
      position = end_of_selector;
      return new (ctx.mem) Selector_Schema(path, line, schema);
    }
  
    Selector_Group* Parser::parse_selector_group()
    {
      To_String to_string;
      Selector_Group* group = new (ctx.mem) Selector_Group(path, line);
      do {
        Selector_Combination* comb = parse_selector_combination();
        if (!comb->has_reference()) {
          size_t sel_line = line;
          Selector_Reference* ref = new (ctx.mem) Selector_Reference(path, sel_line);
          Simple_Selector_Sequence* ref_wrap = new (ctx.mem) Simple_Selector_Sequence(path, sel_line);
          (*ref_wrap) << ref;
          if (!comb->head()) {
            comb->head(ref_wrap);
            comb->has_reference(true);
          }
          else {
            comb = new (ctx.mem) Selector_Combination(path, sel_line, Selector_Combination::ANCESTOR_OF, ref_wrap, comb);
            comb->has_reference(true);
          }
        }
        (*group) << comb;
      }
      while (lex< exactly<','> >());
      return group;
    }
  
    Selector_Combination* Parser::parse_selector_combination()
    {
      size_t sel_line = 0;
      Simple_Selector_Sequence* lhs;
      if (peek< exactly<'+'> >() ||
          peek< exactly<'~'> >() ||
          peek< exactly<'>'> >()) {
        // no selector before the combinator
        lhs = 0;
      }
      else {
        lhs = parse_simple_selector_sequence();
        sel_line = line;
      }
  
      Selector_Combination::Combinator cmb;
      if      (lex< exactly<'+'> >()) cmb = Selector_Combination::ADJACENT_TO;
      else if (lex< exactly<'~'> >()) cmb = Selector_Combination::PRECEDES;
      else if (lex< exactly<'>'> >()) cmb = Selector_Combination::PARENT_OF;
      else                            cmb = Selector_Combination::ANCESTOR_OF;
  
      Selector_Combination* rhs;
      if (peek< exactly<','> >() ||
          peek< exactly<')'> >() ||
          peek< exactly<'{'> >() ||
          peek< exactly<';'> >()) {
        // no selector after the combinator
        rhs = 0;
      }
      else {
        rhs = parse_selector_combination();
        sel_line = line;
      }
      if (!sel_line) sel_line = line;
      return new (ctx.mem) Selector_Combination(path, sel_line, cmb, lhs, rhs);
    }
  
    Simple_Selector_Sequence* Parser::parse_simple_selector_sequence()
    {
      Simple_Selector_Sequence* seq = new (ctx.mem) Simple_Selector_Sequence(path, line);
      // check for backref or type selector, which are only allowed at the front
      if (lex< exactly<'&'> >()) {
        (*seq) << new (ctx.mem) Selector_Reference(path, line);
      }
      else if (lex< sequence< negate< functional >, alternatives< type_selector, universal, string_constant, dimension, percentage, number > > >()) {
        (*seq) << new (ctx.mem) Type_Selector(path, line, lexed);
      }
      else {
        (*seq) << parse_simple_selector();
      }
  
      while (!peek< spaces >(position) &&
             !(peek < exactly<'+'> >(position) ||
               peek < exactly<'~'> >(position) ||
               peek < exactly<'>'> >(position) ||
               peek < exactly<','> >(position) ||
               peek < exactly<')'> >(position) ||
               peek < exactly<'{'> >(position) ||
               peek < exactly<';'> >(position))) {
        (*seq) << parse_simple_selector();
      }
      return seq;
    }
  
    Simple_Selector* Parser::parse_simple_selector()
    {
      if (lex< id_name >() || lex< class_name >()) {
        return new (ctx.mem) Selector_Qualifier(path, line, lexed);
      }
  
      if (lex< string_constant >() || lex< number >()) {
        return new (ctx.mem) Type_Selector(path, line, lexed);
      }
      else if (peek< pseudo_not >()) {
        return parse_negated_selector();
      }
      else if (peek< exactly<':'> >(position) || peek< functional >()) {
        return parse_pseudo_selector();
      }
      else if (peek< exactly<'['> >(position)) {
        return parse_attribute_selector();
      }
      else {
        error("invalid selector after " + lexed);
      }
      // unreachable statement
      return 0;
    }
  
    Negated_Selector* Parser::parse_negated_selector()
    {
      lex< pseudo_not >();
      size_t nline = line;
      Simple_Selector* negated = parse_simple_selector();
      if (!lex< exactly<')'> >()) error("negated selector is missing ')'");
      return new (ctx.mem) Negated_Selector(path, nline, negated);
    }
  
    Pseudo_Selector* Parser::parse_pseudo_selector() {
      if (lex< sequence< pseudo_prefix, functional > >() || lex< functional >()) {
        string name(lexed);
        String* expr = 0;
        if (lex< alternatives< even, odd > >()) {
          expr = new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (peek< binomial >(position)) {
          lex< sequence< optional< coefficient >, exactly<'n'> > >();
          String_Constant* var_coef = new (ctx.mem) String_Constant(path, line, lexed);
          lex< sign >();
          String_Constant* op = new (ctx.mem) String_Constant(path, line, lexed);
          // Binary_Expression::Type op = (lexed == "+" ? Binary_Expression::ADD : Binary_Expression::SUB);
          lex< digits >();
          String_Constant* constant = new (ctx.mem) String_Constant(path, line, lexed);
          // expr = new (ctx.mem) Binary_Expression(path, line, op, var_coef, constant);
          String_Schema* schema = new (ctx.mem) String_Schema(path, line, 3);
          *schema << var_coef << op << constant;
          expr = schema;
        }
        else if (lex< sequence< optional<sign>,
                                optional<digits>,
                                exactly<'n'> > >()) {
          expr = new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (lex< sequence< optional<sign>, digits > >()) {
          expr = new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (lex< identifier >()) {
          expr = new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (lex< string_constant >()) {
          expr = new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (peek< exactly<')'> >()) {
          expr = new (ctx.mem) String_Constant(path, line, "");
        }
        else {
          error("invalid argument to " + name + "...)");
        }
        if (!lex< exactly<')'> >()) error("unterminated argument to " + name + "...)");
        return new (ctx.mem) Pseudo_Selector(path, line, name, expr);
      }
      else if (lex < sequence< pseudo_prefix, identifier > >()) {
        return new (ctx.mem) Pseudo_Selector(path, line, lexed);
      }
      else {
        error("unrecognized pseudo-class or pseudo-element");
      }
      // unreachable statement
      return 0;
    }
  
    Attribute_Selector* Parser::parse_attribute_selector()
    {
      lex< exactly<'['> >();
      if (!lex< type_selector >()) error("invalid attribute name in attribute selector");
      string name(lexed);
      if (lex< exactly<']'> >()) return new (ctx.mem) Attribute_Selector(path, line, name, "", "");
      if (!lex< alternatives< exact_match, class_match, dash_match,
                              prefix_match, suffix_match, substring_match > >()) {
        error("invalid operator in attribute selector for " + name);
      }
      string matcher(lexed);
      if (!lex< string_constant >() && !lex< identifier >()) error("expected a string constant or identifier in attribute selector for " + name);
      string value(lexed);
      if (!lex< exactly<']'> >()) error("unterminated attribute selector for " + name);
      return new (ctx.mem) Attribute_Selector(path, line, name, matcher, value);
    }
  
    Block* Parser::parse_block()
    {
      lex< exactly<'{'> >();
      bool semicolon = false;
      Selector_Lookahead lookahead_result;
      Block* block = new (ctx.mem) Block(path, line);
      while (!lex< exactly<'}'> >()) {
        if (semicolon) {
          if (!lex< exactly<';'> >()) error("non-terminal statement or declaration must end with ';'");
          semicolon = false;
          while (lex< block_comment >()) {
            String_Constant* contents = new (ctx.mem) String_Constant(path, line, lexed);
            Comment*         comment  = new (ctx.mem) Comment(path, line, contents);
            (*block) << comment;
          }
          if (lex< exactly<'}'> >()) break;
        }
        if (lex< block_comment >()) {
          String_Constant* contents = new (ctx.mem) String_Constant(path, line, lexed);
          Comment*         comment  = new (ctx.mem) Comment(path, line, contents);
          (*block) << comment;
        }
        else if (peek< import >(position)) {
          if (stack.back() == mixin_def || stack.back() == function_def) {
            lex< import >(); // to adjust the line number
            error("@import directives are not allowed inside mixins and functions");
          }
          Import* imp = parse_import();
          (*block) << imp;
          if (!imp->files().empty()) {
            for (size_t i = 0, S = imp->files().size(); i < S; ++i) {
              (*block) << new (ctx.mem) Import_Stub(path, line, imp->files()[i]);
            }
          }
          semicolon = true;
        }
        else if (lex< variable >()) {
          (*block) << parse_assignment();
          semicolon = true;
        }
        else if (peek< if_directive >()) {
          (*block) << parse_if_directive();
        }
        else if (peek< for_directive >()) {
          (*block) << parse_for_directive();
        }
        else if (peek< each_directive >()) {
          (*block) << parse_each_directive();
        }
        else if (peek < while_directive >()) {
          (*block) << parse_while_directive();
        }
        else if (lex < return_directive >()) {
          (*block) << new (ctx.mem) Return(path, line, parse_list());
          semicolon = true;
        }
        else if (peek< warn >()) {
          (*block) << parse_warning();
          semicolon = true;
        }
        else if (stack.back() == function_def) {
          error("only variable declarations and control directives are allowed inside functions");
        }
        else if (peek< mixin >() || peek< function >()) {
          (*block) << parse_definition();
        }
        else if (peek< include >(position)) {
          Mixin_Call* the_call = parse_mixin_call();
          (*block) << the_call;
          // don't need a semicolon after a content block
          semicolon = (the_call->block()) ? false : true;
        }
        else if (lex< content >()) {
          if (stack.back() != mixin_def) {
            error("@content may only be used within a mixin");
          }
          (*block) << new (ctx.mem) Content(path, line);
          semicolon = true;
        }
        /*
        else if (peek< exactly<'+'> >()) {
          (*block) << parse_mixin_call();
          semicolon = true;
        }
        */
        else if (lex< extend >()) {
          Selector_Lookahead lookahead = lookahead_for_extension_target(position);
          if (!lookahead.found) error("invalid selector for @extend");
          Selector* target;
          if (lookahead.has_interpolants) target = parse_selector_schema(lookahead.found);
          else                            target = parse_selector_group();
          (*block) << new (ctx.mem) Extension(path, line, target);
          semicolon = true;
        }
        else if (peek< media >()) {
          (*block) << parse_media_block();
        }
        // ignore the @charset directive for now
        else if (lex< exactly< charset_kwd > >()) {
          lex< string_constant >();
          lex< exactly<';'> >();
        }
        else if (peek< at_keyword >()) {
          At_Rule* at_rule = parse_at_rule();
          (*block) << at_rule;
          if (!at_rule->block()) semicolon = true;
        }
        else if ((lookahead_result = lookahead_for_selector(position)).found) {
          (*block) << parse_ruleset(lookahead_result);
        }
        else if (peek< sequence< optional< exactly<'*'> >, alternatives< identifier_schema, identifier >, optional_spaces, exactly<':'>, optional_spaces, exactly<'{'> > >(position)) {
          (*block) << parse_propset();
        }
        else if (!peek< exactly<';'> >()) {
          if (peek< sequence< optional< exactly<'*'> >, identifier_schema, exactly<':'>, exactly<'{'> > >()) {
            (*block) << parse_propset();
          }
          else if (peek< sequence< optional< exactly<'*'> >, identifier, exactly<':'>, exactly<'{'> > >()) {
            (*block) << parse_propset();
          }
          else {
            (*block) << parse_declaration();
            semicolon = true;
          }
        }
        else lex< exactly<';'> >();
        while (lex< block_comment >()) {
          String_Constant* contents = new (ctx.mem) String_Constant(path, line, lexed);
          Comment*         comment  = new (ctx.mem) Comment(path, line, contents);
          (*block) << comment;
        }
      }
      return block;
    }
  
    Declaration* Parser::parse_declaration() {
      String* prop = 0;
      if (peek< sequence< optional< exactly<'*'> >, identifier_schema > >()) {
        prop = parse_identifier_schema();
      }
      else if (lex< sequence< optional< exactly<'*'> >, identifier > >()) {
        prop = new (ctx.mem) String_Constant(path, line, lexed);
      }
      else {
        error("invalid property name");
      }
      if (!lex< exactly<':'> >()) error("property \"" + string(lexed) + "\" must be followed by a ':'");
      if (peek< exactly<';'> >()) error("style declaration must contain a value");
      Expression* list = parse_list();
      return new (ctx.mem) Declaration(path, prop->line(), prop, list, lex<important>());
    }
  
    Expression* Parser::parse_list()
    {
      return parse_comma_list();
    }
  
    Expression* Parser::parse_comma_list()
    {
      if (peek< exactly<'!'> >(position) ||
          peek< exactly<';'> >(position) ||
          peek< exactly<'}'> >(position) ||
          peek< exactly<'{'> >(position) ||
          peek< exactly<')'> >(position) ||
          peek< exactly<':'> >(position) ||
          peek< exactly<ellipsis> >(position))
      { return new (ctx.mem) List(path, line, 0); }
      Expression* list1 = parse_space_list();
      // if it's a singleton, return it directly; don't wrap it
      if (!peek< exactly<','> >(position)) return list1;
  
      List* comma_list = new (ctx.mem) List(path, line, 2, List::COMMA);
      (*comma_list) << list1;
  
      while (lex< exactly<','> >())
      {
        Expression* list = parse_space_list();
        (*comma_list) << list;
      }
  
      return comma_list;
    }
  
    Expression* Parser::parse_space_list()
    {
      Expression* disj1 = parse_disjunction();
      // if it's a singleton, return it directly; don't wrap it
      if (peek< exactly<'!'> >(position) ||
          peek< exactly<';'> >(position) ||
          peek< exactly<'}'> >(position) ||
          peek< exactly<'{'> >(position) ||
          peek< exactly<')'> >(position) ||
          peek< exactly<','> >(position) ||
          peek< exactly<':'> >(position) ||
          peek< exactly<ellipsis> >(position) ||
          peek< default_flag >(position))
      { return disj1; }
  
      List* space_list = new (ctx.mem) List(path, line, 2, List::SPACE);
      (*space_list) << disj1;
  
      while (!(peek< exactly<'!'> >(position) ||
               peek< exactly<';'> >(position) ||
               peek< exactly<'}'> >(position) ||
               peek< exactly<'{'> >(position) ||
               peek< exactly<')'> >(position) ||
               peek< exactly<','> >(position) ||
               peek< exactly<':'> >(position) ||
               peek< exactly<ellipsis> >(position) ||
               peek< default_flag >(position)))
      {
        (*space_list) << parse_disjunction();
      }
  
      return space_list;
    }
  
    Expression* Parser::parse_disjunction()
    {
      Expression* conj1 = parse_conjunction();
      // if it's a singleton, return it directly; don't wrap it
      if (!peek< sequence< or_op, negate< identifier > > >()) return conj1;
  
      vector<Expression*> operands;
      while (lex< sequence< or_op, negate< identifier > > >())
        operands.push_back(parse_conjunction());
  
      return fold_operands(conj1, operands, Binary_Expression::OR);
    }
  
    Expression* Parser::parse_conjunction()
    {
      Expression* rel1 = parse_relation();
      // if it's a singleton, return it directly; don't wrap it
      if (!peek< sequence< and_op, negate< identifier > > >()) return rel1;
  
      vector<Expression*> operands;
      while (lex< sequence< and_op, negate< identifier > > >())
        operands.push_back(parse_relation());
  
      return fold_operands(rel1, operands, Binary_Expression::AND);
    }
  
    Expression* Parser::parse_relation()
    {
      Expression* expr1 = parse_expression();
      // if it's a singleton, return it directly; don't wrap it
      if (!(peek< eq_op >(position)  ||
            peek< neq_op >(position) ||
            peek< gte_op >(position) ||
            peek< gt_op >(position)  ||
            peek< lte_op >(position) ||
            peek< lt_op >(position)))
      { return expr1; }
  
      Binary_Expression::Type op
      = lex<eq_op>()  ? Binary_Expression::EQ
      : lex<neq_op>() ? Binary_Expression::NEQ
      : lex<gte_op>() ? Binary_Expression::GTE
      : lex<lte_op>() ? Binary_Expression::LTE
      : lex<gt_op>()  ? Binary_Expression::GT
      : lex<lt_op>()  ? Binary_Expression::LT
      :                 Binary_Expression::LT; // whatever
  
      Expression* expr2 = parse_expression();
  
      return new (ctx.mem) Binary_Expression(path, expr1->line(), op, expr1, expr2);
    }
  
    Expression* Parser::parse_expression()
    {
      Expression* term1 = parse_term();
      // if it's a singleton, return it directly; don't wrap it
      if (!(peek< exactly<'+'> >(position) ||
            peek< sequence< negate< number >, exactly<'-'> > >(position)))
      { return term1; }
  
      vector<Expression*> operands;
      vector<Binary_Expression::Type> operators;
      while (lex< exactly<'+'> >() || lex< sequence< negate< number >, exactly<'-'> > >()) {
        operators.push_back(lexed == "+" ? Binary_Expression::ADD : Binary_Expression::SUB);
        operands.push_back(parse_term());
      }
  
      return fold_operands(term1, operands, operators);
    }
  
    Expression* Parser::parse_term()
    {
      Expression* fact1 = parse_factor();
      // if it's a singleton, return it directly; don't wrap it
      if (!(peek< exactly<'*'> >(position) ||
            peek< exactly<'/'> >(position) ||
            peek< exactly<'%'> >(position)))
      { return fact1; }
  
      vector<Expression*> operands;
      vector<Binary_Expression::Type> operators;
      while (lex< exactly<'*'> >() || lex< exactly<'/'> >() || lex< exactly<'%'> >()) {
        if      (lexed == "*") operators.push_back(Binary_Expression::MUL);
        else if (lexed == "/") operators.push_back(Binary_Expression::DIV);
        else                   operators.push_back(Binary_Expression::MOD);
        operands.push_back(parse_factor());
      }
  
      return fold_operands(fact1, operands, operators);
    }
  
    Expression* Parser::parse_factor()
    {
      if (lex< exactly<'('> >()) {
        Expression* value = parse_comma_list();
        if (!lex< exactly<')'> >()) error("unclosed parenthesis");
        value->is_delayed(false);
        if (value->concrete_type() == Expression::LIST) {
          List* l = static_cast<List*>(value);
          if (!l->empty()) (*l)[0]->is_delayed(false);
        }
        return value;
      }
      else if (lex< sequence< exactly<'+'>, spaces_and_comments, negate< number > > >()) {
        return new (ctx.mem) Unary_Expression(path, line, Unary_Expression::PLUS, parse_factor());
      }
      else if (lex< sequence< exactly<'-'>, spaces_and_comments, negate< number> > >()) {
        return new (ctx.mem) Unary_Expression(path, line, Unary_Expression::MINUS, parse_factor());
      }
      else {
        return parse_value();
      }
    }
  
    Expression* Parser::parse_value()
    {
      if (lex< uri_prefix >()) {
        // TODO: really need to clean up this chunk
        Arguments* args = new (ctx.mem) Arguments(path, line);
        Function_Call* result = new (ctx.mem) Function_Call(path, line, "url", args);
        // gah, gonna have to use exception handling to do backtracking ...
        const char* here = position;
        try {
          Expression* expr = parse_list();
          (*args) << new (ctx.mem) Argument(path, line, expr);
        }
        catch (Error& e) {
          position = here;
          if (peek< sequence< url_schema, spaces_and_comments, exactly<')'> > >()) {
            lex< url_schema >();
            String_Schema* the_url = Parser::from_token(lexed, ctx, path, line).parse_url_schema();
            (*args) << new (ctx.mem) Argument(path, line, the_url);
          }
          else if (peek< sequence< url_value, spaces_and_comments, exactly<')'> > >()) {
            lex< url_value >();
            String_Constant* the_url = new (ctx.mem) String_Constant(path, line, lexed);
            (*args) << new (ctx.mem) Argument(path, line, the_url);
          }
          else {
            const char* value = position;
            const char* rparen = find_first< exactly<')'> >(position);
            if (!rparen) error("URI is missing ')'");
            Token content_tok(Token(value, rparen));
            String_Constant* content_node = new (ctx.mem) String_Constant(path, line, content_tok);
            (*args) << new (ctx.mem) Argument(path, line, content_node);
            position = rparen;
          }
        }
        if (!lex< exactly<')'> >()) error("URI is missing ')'");
        return result;
      }
  
      if (peek< functional_schema >())
      { return parse_function_call_schema(); }
  
      if (peek< functional >())
      { return parse_function_call(); }
  
      if (lex< value_schema >())
      { return Parser::from_token(lexed, ctx, path, line).parse_value_schema(); }
  
      if (lex< sequence< true_val, negate< identifier > > >())
      { return new (ctx.mem) Boolean(path, line, true); }
  
      if (lex< sequence< false_val, negate< identifier > > >())
      { return new (ctx.mem) Boolean(path, line, false); }
  
      if (lex< sequence< null, negate< identifier > > >())
      { return new (ctx.mem) Null(path, line); }
  
      if (lex< identifier >()) {
        String_Constant* str = new (ctx.mem) String_Constant(path, line, lexed);
        str->is_delayed(true);
        return str;
      }
  
      if (lex< percentage >())
      { return new (ctx.mem) Textual(path, line, Textual::PERCENTAGE, lexed); }
  
      if (lex< dimension >())
      { return new (ctx.mem) Textual(path, line, Textual::DIMENSION, lexed); }
  
      if (lex< number >())
      { return new (ctx.mem) Textual(path, line, Textual::NUMBER, lexed); }
  
      if (lex< hex >())
      { return new (ctx.mem) Textual(path, line, Textual::HEX, lexed); }
  
      if (peek< string_constant >())
      { return parse_string(); }
  
      if (lex< variable >())
      { return new (ctx.mem) Variable(path, line, lexed); }
  
      error("error reading values after " + lexed);
  
      // unreachable statement
      return 0;
    }
  
    String* Parser::parse_string()
    {
      lex< string_constant >();
      Token str(lexed);
      const char* i = str.begin;
      // see if there any interpolants
      const char* p = find_first_in_interval< sequence< negate< exactly<'\\'> >, exactly<hash_lbrace> > >(str.begin, str.end);
      if (!p) {
        String_Constant* str_node = new (ctx.mem) String_Constant(path, line, str);
        str_node->is_delayed(true);
        return str_node;
      }
  
      String_Schema* schema = new (ctx.mem) String_Schema(path, line);
      schema->quote_mark(*str.begin);
      while (i < str.end) {
        p = find_first_in_interval< sequence< negate< exactly<'\\'> >, exactly<hash_lbrace> > >(i, str.end);
        if (p) {
          if (i < p) {
            (*schema) << new (ctx.mem) String_Constant(path, line, Token(i, p)); // accumulate the preceding segment if it's nonempty
          }
          const char* j = find_first_in_interval< exactly<rbrace> >(p, str.end); // find the closing brace
          if (j) {
            // parse the interpolant and accumulate it
            Expression* interp_node = Parser::from_token(Token(p+2, j), ctx, path, line).parse_list();
            interp_node->is_interpolant(true);
            (*schema) << interp_node;
            i = j+1;
          }
          else {
            // throw an error if the interpolant is unterminated
            error("unterminated interpolant inside string constant " + str);
          }
        }
        else { // no interpolants left; add the last segment if nonempty
          if (i < str.end) (*schema) << new (ctx.mem) String_Constant(path, line, Token(i, str.end));
          break;
        }
      }
      return schema;
    }
  
    String_Schema* Parser::parse_value_schema()
    {
      String_Schema* schema = new (ctx.mem) String_Schema(path, line);
  
      while (position < end) {
        if (lex< interpolant >()) {
          Token insides(Token(lexed.begin + 2, lexed.end - 1));
          Expression* interp_node = Parser::from_token(insides, ctx, path, line).parse_list();
          interp_node->is_interpolant(true);
          (*schema) << interp_node;
        }
        else if (lex< identifier >()) {
          (*schema) << new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (lex< percentage >()) {
          (*schema) << new (ctx.mem) Textual(path, line, Textual::PERCENTAGE, lexed);
        }
        else if (lex< dimension >()) {
          (*schema) << new (ctx.mem) Textual(path, line, Textual::DIMENSION, lexed);
        }
        else if (lex< number >()) {
          (*schema) << new (ctx.mem) Textual(path, line, Textual::NUMBER, lexed);
        }
        else if (lex< hex >()) {
          (*schema) << new (ctx.mem) Textual(path, line, Textual::HEX, lexed);
        }
        else if (lex< string_constant >()) {
          (*schema) << new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (lex< variable >()) {
          (*schema) << new (ctx.mem) Variable(path, line, lexed);
        }
        else {
          error("error parsing interpolated value");
        }
      }
      return schema;
    }
  
    String_Schema* Parser::parse_url_schema()
    {
      String_Schema* schema = new (ctx.mem) String_Schema(path, line);
  
      while (position < end) {
        if (position[0] == '/') {
          lexed = Token(position, position+1);
          (*schema) << new (ctx.mem) String_Constant(path, line, lexed);
          ++position;
        }
        else if (lex< interpolant >()) {
          Token insides(Token(lexed.begin + 2, lexed.end - 1));
          Expression* interp_node = Parser::from_token(insides, ctx, path, line).parse_list();
          interp_node->is_interpolant(true);
          (*schema) << interp_node;
        }
        else if (lex< sequence< identifier, exactly<':'> > >()) {
          (*schema) << new (ctx.mem) String_Constant(path, line, lexed);
        }
        else if (lex< filename >()) {
          (*schema) << new (ctx.mem) String_Constant(path, line, lexed);
        }
        else {
          error("error parsing interpolated url");
        }
      }
      return schema;
    }
  
    String* Parser::parse_identifier_schema()
    {
      lex< sequence< optional< exactly<'*'> >, identifier_schema > >();
      Token id(lexed);
      const char* i = id.begin;
      // see if there any interpolants
      const char* p = find_first_in_interval< sequence< negate< exactly<'\\'> >, exactly<hash_lbrace> > >(id.begin, id.end);
      if (!p) {
        return new (ctx.mem) String_Constant(path, line, id);
      }
  
      String_Schema* schema = new (ctx.mem) String_Schema(path, line);
      while (i < id.end) {
        p = find_first_in_interval< sequence< negate< exactly<'\\'> >, exactly<hash_lbrace> > >(i, id.end);
        if (p) {
          if (i < p) {
            (*schema) << new (ctx.mem) String_Constant(path, line, Token(i, p)); // accumulate the preceding segment if it's nonempty
          }
          const char* j = find_first_in_interval< exactly<rbrace> >(p, id.end); // find the closing brace
          if (j) {
            // parse the interpolant and accumulate it
            Expression* interp_node = Parser::from_token(Token(p+2, j), ctx, path, line).parse_list();
            interp_node->is_interpolant(true);
            (*schema) << interp_node;
            i = j+1;
          }
          else {
            // throw an error if the interpolant is unterminated
            error("unterminated interpolant inside interpolated identifier " + id);
          }
        }
        else { // no interpolants left; add the last segment if nonempty
          if (i < id.end) (*schema) << new (ctx.mem) String_Constant(path, line, Token(i, id.end));
          break;
        }
      }
      return schema;
    }
  
    Function_Call* Parser::parse_function_call()
    {
      lex< identifier >();
      string name(lexed);
      size_t line_of_call = line;
  
      Function_Call* the_call = new (ctx.mem) Function_Call(path, line_of_call, name, parse_arguments());
      return the_call;
    }
  
    Function_Call_Schema* Parser::parse_function_call_schema()
    {
      String* name = parse_identifier_schema();
      size_t line_of_call = line;
  
      Function_Call_Schema* the_call = new (ctx.mem) Function_Call_Schema(path, line_of_call, name, parse_arguments());
      return the_call;
    }
  
    If* Parser::parse_if_directive(bool else_if)
    {
      lex< if_directive >() || (else_if && lex< exactly<if_after_else_kwd> >());
      size_t if_line = line;
      Expression* predicate = parse_list();
      predicate->is_delayed(false);
      if (!peek< exactly<'{'> >()) error("expected '{' after the predicate for @if");
      Block* consequent = parse_block();
      Block* alternative = 0;
      if (lex< else_directive >()) {
        if (peek< exactly<if_after_else_kwd> >()) {
          alternative = new (ctx.mem) Block(path, line);
          (*alternative) << parse_if_directive(true);
        }
        else if (!peek< exactly<'{'> >()) {
          error("expected '{' after @else");
        }
        else {
          alternative = parse_block();
        }
      }
      return new (ctx.mem) If(path, if_line, predicate, consequent, alternative);
    }
  
    For* Parser::parse_for_directive()
    {
      lex< for_directive >();
      size_t for_line = line;
      if (!lex< variable >()) error("@for directive requires an iteration variable");
      string var(lexed);
      if (!lex< from >()) error("expected 'from' keyword in @for directive");
      Expression* lower_bound = parse_expression();
      lower_bound->is_delayed(false);
      bool inclusive = false;
      if (lex< through >()) inclusive = true;
      else if (lex< to >()) inclusive = false;
      else                  error("expected 'through' or 'to' keywod in @for directive");
      Expression* upper_bound = parse_expression();
      upper_bound->is_delayed(false);
      if (!peek< exactly<'{'> >()) error("expected '{' after the upper bound in @for directive");
      Block* body = parse_block();
      return new (ctx.mem) For(path, for_line, var, lower_bound, upper_bound, body, inclusive);
    }
  
    Each* Parser::parse_each_directive()
    {
      lex < each_directive >();
      size_t each_line = line;
      if (!lex< variable >()) error("@each directive requires an iteration variable");
      string var(lexed);
      if (!lex< in >()) error("expected 'in' keyword in @each directive");
      Expression* list = parse_list();
      list->is_delayed(false);
      if (list->concrete_type() == Expression::LIST) {
        List* l = static_cast<List*>(list);
        for (size_t i = 0, L = l->length(); i < L; ++i) {
          (*l)[i]->is_delayed(false);
        }
      }
      if (!peek< exactly<'{'> >()) error("expected '{' after the upper bound in @each directive");
      Block* body = parse_block();
      return new (ctx.mem) Each(path, each_line, var, list, body);
    }
  
    While* Parser::parse_while_directive()
    {
      lex< while_directive >();
      size_t while_line = line;
      Expression* predicate = parse_list();
      predicate->is_delayed(false);
      Block* body = parse_block();
      return new (ctx.mem) While(path, while_line, predicate, body);
    }
  
    Media_Block* Parser::parse_media_block()
    {
      lex< media >();
      size_t media_line = line;
  
      List* media_queries = parse_media_queries();
  
      if (!peek< exactly<'{'> >()) {
        error("expected '{' in media query");
      }
      Block* block = parse_block();
  
      return new (ctx.mem) Media_Block(path, media_line, media_queries, block);
    }
  
    List* Parser::parse_media_queries()
    {
      List* media_queries = new (ctx.mem) List(path, line, 0, List::COMMA);
      if (!peek< exactly<'{'> >()) (*media_queries) << parse_media_query();
      while (lex< exactly<','> >()) (*media_queries) << parse_media_query();
      return media_queries;
    }
  
    // Expression* Parser::parse_media_query()
    Media_Query* Parser::parse_media_query()
    {
      Media_Query* media_query = new (ctx.mem) Media_Query(path, line);
  
      if (lex< exactly< not_kwd > >()) media_query->is_negated(true);
      else if (lex< exactly< only_kwd > >()) media_query->is_restricted(true);
  
      if (peek< identifier_schema >()) media_query->media_type(parse_identifier_schema());
      else if (lex< identifier >())    media_query->media_type(new (ctx.mem) String_Constant(path, line, lexed));
      else                             (*media_query) << parse_media_expression();
  
      while (lex< exactly< and_kwd > >()) (*media_query) << parse_media_expression();
  
      return media_query;
    }
  
    Media_Query_Expression* Parser::parse_media_expression()
    {
      if (peek< identifier_schema >()) {
        String* ss = parse_identifier_schema();
        return new (ctx.mem) Media_Query_Expression(path, line, ss, 0, true);
      }
      if (!lex< exactly<'('> >()) {
        error("media query expression must begin with '('");
      }
      Expression* feature = 0;
      if (peek< exactly<')'> >()) {
        error("media feature required in media query expression");
      }
      feature = parse_list();
      Expression* expression = 0;
      if (lex< exactly<':'> >()) {
        expression = parse_list();
      }
      if (!lex< exactly<')'> >()) {
        error("unclosed parenthesis in media query expression");
      }
      return new (ctx.mem) Media_Query_Expression(path, feature->line(), feature, expression);
    }
  
    At_Rule* Parser::parse_at_rule()
    {
      lex<at_keyword>();
      string kwd(lexed);
      size_t at_line = line;
      Selector* sel = 0;
      Selector_Lookahead lookahead = lookahead_for_extension_target(position);
      if (lookahead.found) {
        if (lookahead.has_interpolants) {
          sel = parse_selector_schema(lookahead.found);
        }
        else {
          sel = parse_selector_group();
        }
      }
      Block* body = 0;
      if (peek< exactly<'{'> >()) body = parse_block();
      return new (ctx.mem) At_Rule(path, at_line, kwd, sel, body);
    }
  
    Warning* Parser::parse_warning()
    {
      lex< warn >();
      return new (ctx.mem) Warning(path, line, parse_list());
    }
  
    Selector_Lookahead Parser::lookahead_for_selector(const char* start)
    {
      const char* p = start ? start : position;
      const char* q;
      bool saw_interpolant = false;
  
      while ((q = peek< identifier >(p))                             ||
             (q = peek< type_selector >(p))                          ||
             (q = peek< id_name >(p))                                ||
             (q = peek< class_name >(p))                             ||
             (q = peek< sequence< pseudo_prefix, identifier > >(p))  ||
             (q = peek< percentage >(p))                             ||
             (q = peek< dimension >(p))                              ||
             (q = peek< string_constant >(p))                        ||
             (q = peek< exactly<'*'> >(p))                           ||
             (q = peek< exactly<'('> >(p))                           ||
             (q = peek< exactly<')'> >(p))                           ||
             (q = peek< exactly<'['> >(p))                           ||
             (q = peek< exactly<']'> >(p))                           ||
             (q = peek< exactly<'+'> >(p))                           ||
             (q = peek< exactly<'~'> >(p))                           ||
             (q = peek< exactly<'>'> >(p))                           ||
             (q = peek< exactly<','> >(p))                           ||
             (q = peek< binomial >(p))                               ||
             (q = peek< sequence< optional<sign>,
                                  optional<digits>,
                                  exactly<'n'> > >(p))               ||
             (q = peek< sequence< optional<sign>,
                                  digits > >(p))                     ||
             (q = peek< number >(p))                                 ||
             (q = peek< exactly<'&'> >(p))                           ||
             (q = peek< alternatives<exact_match,
                                     class_match,
                                     dash_match,
                                     prefix_match,
                                     suffix_match,
                                     substring_match> >(p))          ||
             (q = peek< sequence< exactly<'.'>, interpolant > >(p))  ||
             (q = peek< sequence< exactly<'#'>, interpolant > >(p))  ||
             (q = peek< sequence< exactly<'-'>, interpolant > >(p))  ||
             (q = peek< sequence< pseudo_prefix, interpolant > >(p)) ||
             (q = peek< interpolant >(p))) {
        p = q;
        if (*(p - 1) == '}') saw_interpolant = true;
      }
  
      Selector_Lookahead result;
      result.found            = peek< exactly<'{'> >(p) ? p : 0;
      result.has_interpolants = saw_interpolant;
  
      return result;
    }
  
    Selector_Lookahead Parser::lookahead_for_extension_target(const char* start)
    {
      const char* p = start ? start : position;
      const char* q;
      bool saw_interpolant = false;
      bool saw_stuff = false;
  
      while ((q = peek< identifier >(p))                             ||
             (q = peek< type_selector >(p))                          ||
             (q = peek< id_name >(p))                                ||
             (q = peek< class_name >(p))                             ||
             (q = peek< sequence< pseudo_prefix, identifier > >(p))  ||
             (q = peek< percentage >(p))                             ||
             (q = peek< dimension >(p))                              ||
             (q = peek< string_constant >(p))                        ||
             (q = peek< exactly<'*'> >(p))                           ||
             (q = peek< exactly<'('> >(p))                           ||
             (q = peek< exactly<')'> >(p))                           ||
             (q = peek< exactly<'['> >(p))                           ||
             (q = peek< exactly<']'> >(p))                           ||
             (q = peek< exactly<'+'> >(p))                           ||
             (q = peek< exactly<'~'> >(p))                           ||
             (q = peek< exactly<'>'> >(p))                           ||
             (q = peek< exactly<','> >(p))                           ||
             (q = peek< binomial >(p))                               ||
             (q = peek< sequence< optional<sign>,
                                  optional<digits>,
                                  exactly<'n'> > >(p))               ||
             (q = peek< sequence< optional<sign>,
                                  digits > >(p))                     ||
             (q = peek< number >(p))                                 ||
             (q = peek< exactly<'&'> >(p))                           ||
             (q = peek< alternatives<exact_match,
                                     class_match,
                                     dash_match,
                                     prefix_match,
                                     suffix_match,
                                     substring_match> >(p))          ||
             (q = peek< sequence< exactly<'.'>, interpolant > >(p))  ||
             (q = peek< sequence< exactly<'#'>, interpolant > >(p))  ||
             (q = peek< sequence< exactly<'-'>, interpolant > >(p))  ||
             (q = peek< sequence< pseudo_prefix, interpolant > >(p)) ||
             (q = peek< interpolant >(p))) {
        p = q;
        if (*(p - 1) == '}') saw_interpolant = true;
        saw_stuff = true;
      }
  
      Selector_Lookahead result;
      result.found            = peek< alternatives< exactly<';'>, exactly<'}'>, exactly<'{'> > >(p) && saw_stuff ? p : 0;
      result.has_interpolants = saw_interpolant;
  
      return result;
    }
  
    void Parser::read_bom()
    {
      size_t skip = 0;
      string encoding;
      bool utf_8 = false;
      switch ((unsigned char) source[0]) {
      case 0xEF:
        skip = check_bom_chars(source, utf_8_bom, 3);
        encoding = "UTF-8";
        utf_8 = true;
        break;
      case 0xFE:
        skip = check_bom_chars(source, utf_16_bom_be, 2);
        encoding = "UTF-16 (big endian)";
        break;
      case 0xFF:
        skip = check_bom_chars(source, utf_16_bom_le, 2);
        skip += (skip ? check_bom_chars(source, utf_32_bom_le, 4) : 0);
        encoding = (skip == 2 ? "UTF-16 (little endian)" : "UTF-32 (little endian)");
        break;
      case 0x00:
        skip = check_bom_chars(source, utf_32_bom_be, 4);
        encoding = "UTF-32 (big endian)";
        break;
      case 0x2B:
        skip = check_bom_chars(source, utf_7_bom_1, 4)
             | check_bom_chars(source, utf_7_bom_2, 4)
             | check_bom_chars(source, utf_7_bom_3, 4)
             | check_bom_chars(source, utf_7_bom_4, 4)
             | check_bom_chars(source, utf_7_bom_5, 5);
        encoding = "UTF-7";
        break;
      case 0xF7:
        skip = check_bom_chars(source, utf_1_bom, 3);
        encoding = "UTF-1";
        break;
      case 0xDD:
        skip = check_bom_chars(source, utf_ebcdic_bom, 4);
        encoding = "UTF-EBCDIC";
        break;
      case 0x0E:
        skip = check_bom_chars(source, scsu_bom, 3);
        encoding = "SCSU";
        break;
      case 0xFB:
        skip = check_bom_chars(source, bocu_1_bom, 3);
        encoding = "BOCU-1";
        break;
      case 0x84:
        skip = check_bom_chars(source, gb_18030_bom, 4);
        encoding = "GB-18030";
        break;
      }
      if (skip > 0 && !utf_8) error("only UTF-8 documents are currently supported; your document appears to be " + encoding);
      position += skip;
    }
  
    size_t check_bom_chars(const char* src, const unsigned char* bom, size_t len)
    {
      size_t skip = 0;
      for (size_t i = 0; i < len; ++i, ++skip) {
        if ((unsigned char) src[i] != bom[i]) return 0;
      }
      return skip;
    }
  
  
    Expression* Parser::fold_operands(Expression* base, vector<Expression*>& operands, Binary_Expression::Type op)
    {
      for (size_t i = 0, S = operands.size(); i < S; ++i) {
        base = new (ctx.mem) Binary_Expression(path, line, op, base, operands[i]);
        Binary_Expression* b = static_cast<Binary_Expression*>(base);
        if (op == Binary_Expression::DIV && b->left()->is_delayed() && b->right()->is_delayed()) {
          base->is_delayed(true);
        }
        else {
          b->left()->is_delayed(false);
          b->right()->is_delayed(false);
        }
      }
      return base;
    }
  
    Expression* Parser::fold_operands(Expression* base, vector<Expression*>& operands, vector<Binary_Expression::Type>& ops)
    {
      for (size_t i = 0, S = operands.size(); i < S; ++i) {
        base = new (ctx.mem) Binary_Expression(path, line, ops[i], base, operands[i]);
        Binary_Expression* b = static_cast<Binary_Expression*>(base);
        if (ops[i] == Binary_Expression::DIV && b->left()->is_delayed() && b->right()->is_delayed()) {
          base->is_delayed(true);
        }
        else {
          b->left()->is_delayed(false);
          b->right()->is_delayed(false);
        }
      }
      return base;
    }
  
    void Parser::error(string msg, size_t ln)
    {
      throw Error(Error::syntax, path, ln ? ln : line, msg);
    }
  
  }
  