text: // sass.hpp must go before all system headers to get the
  // __EXTENSIONS__ fix on Solaris.
  #include "sass.hpp"
  
  #include "parser.hpp"
  #include "color_maps.hpp"
  #include "util_string.hpp"
  
  // Notes about delayed: some ast nodes can have delayed evaluation so
  // they can preserve their original semantics if needed. This is most
  // prominently exhibited by the division operation, since it is not
  // only a valid operation, but also a valid css statement (i.e. for
  // fonts, as in `16px/24px`). When parsing lists and expression we
  // unwrap single items from lists and other operations. A nested list
  // must not be delayed, only the items of the first level sometimes
  // are delayed (as with argument lists). To achieve this we need to
  // pass status to the list parser, so this can be set correctly.
  // Another case with delayed values are colors. In compressed mode
  // only processed values get compressed (other are left as written).
  
  
  namespace Sass {
    using namespace Constants;
    using namespace Prelexer;
  
    Parser Parser::from_c_str(const char* beg, Context& ctx, Backtraces traces, ParserState pstate, const char* source, bool allow_parent)
    {
      pstate.offset.column = 0;
      pstate.offset.line = 0;
      Parser p(ctx, pstate, traces, allow_parent);
      p.source   = source ? source : beg;
      p.position = beg ? beg : p.source;
      p.end      = p.position + strlen(p.position);
      Block_Obj root = SASS_MEMORY_NEW(Block, pstate);
      p.block_stack.push_back(root);
      root->is_root(true);
      return p;
    }
  
    Parser Parser::from_c_str(const char* beg, const char* end, Context& ctx, Backtraces traces, ParserState pstate, const char* source, bool allow_parent)
    {
      pstate.offset.column = 0;
      pstate.offset.line = 0;
      Parser p(ctx, pstate, traces, allow_parent);
      p.source   = source ? source : beg;
      p.position = beg ? beg : p.source;
      p.end      = end ? end : p.position + strlen(p.position);
      Block_Obj root = SASS_MEMORY_NEW(Block, pstate);
      p.block_stack.push_back(root);
      root->is_root(true);
      return p;
    }
  
     void Parser::advanceToNextToken() {
        lex < css_comments >(false);
        // advance to position
        pstate += pstate.offset;
        pstate.offset.column = 0;
        pstate.offset.line = 0;
      }
  
    SelectorListObj Parser::parse_selector(const char* beg, Context& ctx, Backtraces traces, ParserState pstate, const char* source, bool allow_parent)
    {
      Parser p = Parser::from_c_str(beg, ctx, traces, pstate, source, allow_parent);
      // ToDo: remap the source-map entries somehow
      return p.parseSelectorList(false);
    }
  
    bool Parser::peek_newline(const char* start)
    {
      return peek_linefeed(start ? start : position)
             && ! peek_css<exactly<'{'>>(start);
    }
  
    Parser Parser::from_token(Token t, Context& ctx, Backtraces traces, ParserState pstate, const char* source)
    {
      Parser p(ctx, pstate, traces);
      p.source   = source ? source : t.begin;
      p.position = t.begin ? t.begin : p.source;
      p.end      = t.end ? t.end : p.position + strlen(p.position);
      Block_Obj root = SASS_MEMORY_NEW(Block, pstate);
      p.block_stack.push_back(root);
      root->is_root(true);
      return p;
    }
  
    /* main entry point to parse root block */
    Block_Obj Parser::parse()
    {
  
      // consume unicode BOM
      read_bom();
  
      // scan the input to find invalid utf8 sequences
      const char* it = utf8::find_invalid(position, end);
  
      // report invalid utf8
      if (it != end) {
        pstate += Offset::init(position, it);
        traces.push_back(Backtrace(pstate));
        throw Exception::InvalidSass(pstate, traces, "Invalid UTF-8 sequence");
      }
  
      // create a block AST node to hold children
      Block_Obj root = SASS_MEMORY_NEW(Block, pstate, 0, true);
  
      // check seems a bit esoteric but works
      if (ctx.resources.size() == 1) {
        // apply headers only on very first include
        ctx.apply_custom_headers(root, path, pstate);
      }
  
      // parse children nodes
      block_stack.push_back(root);
      parse_block_nodes(true);
      block_stack.pop_back();
  
      // update final position
      root->update_pstate(pstate);
  
      if (position != end) {
        css_error("Invalid CSS", " after ", ": expected selector or at-rule, was ");
      }
  
      return root;
    }
  
  
    // convenience function for block parsing
    // will create a new block ad-hoc for you
    // this is the base block parsing function
    Block_Obj Parser::parse_css_block(bool is_root)
    {
  
      // parse comments before block
      // lex < optional_css_comments >();
  
      // lex mandatory opener or error out
      if (!lex_css < exactly<'{'> >()) {
        css_error("Invalid CSS", " after ", ": expected \"{\", was ");
      }
      // create new block and push to the selector stack
      Block_Obj block = SASS_MEMORY_NEW(Block, pstate, 0, is_root);
      block_stack.push_back(block);
  
      if (!parse_block_nodes(is_root)) css_error("Invalid CSS", " after ", ": expected \"}\", was ");
  
      if (!lex_css < exactly<'}'> >()) {
        css_error("Invalid CSS", " after ", ": expected \"}\", was ");
      }
  
      // update for end position
      // this seems to be done somewhere else
      // but that fixed selector schema issue
      // block->update_pstate(pstate);
  
      // parse comments after block
      // lex < optional_css_comments >();
  
      block_stack.pop_back();
  
      return block;
    }
  
    // convenience function for block parsing
    // will create a new block ad-hoc for you
    // also updates the `in_at_root` flag
    Block_Obj Parser::parse_block(bool is_root)
    {
      return parse_css_block(is_root);
    }
  
    // the main block parsing function
    // parses stuff between `{` and `}`
    bool Parser::parse_block_nodes(bool is_root)
    {
  
      // loop until end of string
      while (position < end) {
  
        // we should be able to refactor this
        parse_block_comments();
        lex < css_whitespace >();
  
        if (lex < exactly<';'> >()) continue;
        if (peek < end_of_file >()) return true;
        if (peek < exactly<'}'> >()) return true;
  
        if (parse_block_node(is_root)) continue;
  
        parse_block_comments();
  
        if (lex_css < exactly<';'> >()) continue;
        if (peek_css < end_of_file >()) return true;
        if (peek_css < exactly<'}'> >()) return true;
  
        // illegal sass
        return false;
      }
      // return success
      return true;
    }
  
    // parser for a single node in a block
    // semicolons must be lexed beforehand
    bool Parser::parse_block_node(bool is_root) {
  
      Block_Obj block = block_stack.back();
  
      parse_block_comments();
  
      // throw away white-space
      // includes line comments
      lex < css_whitespace >();
  
      Lookahead lookahead_result;
  
      // also parse block comments
  
      // first parse everything that is allowed in functions
      if (lex < variable >(true)) { block->append(parse_assignment()); }
      else if (lex < kwd_err >(true)) { block->append(parse_error()); }
      else if (lex < kwd_dbg >(true)) { block->append(parse_debug()); }
      else if (lex < kwd_warn >(true)) { block->append(parse_warning()); }
      else if (lex < kwd_if_directive >(true)) { block->append(parse_if_directive()); }
      else if (lex < kwd_for_directive >(true)) { block->append(parse_for_directive()); }
      else if (lex < kwd_each_directive >(true)) { block->append(parse_each_directive()); }
      else if (lex < kwd_while_directive >(true)) { block->append(parse_while_directive()); }
      else if (lex < kwd_return_directive >(true)) { block->append(parse_return_directive()); }
  
      // parse imports to process later
      else if (lex < kwd_import >(true)) {
        Scope parent = stack.empty() ? Scope::Rules : stack.back();
        if (parent != Scope::Function && parent != Scope::Root && parent != Scope::Rules && parent != Scope::Media) {
          if (! peek_css< uri_prefix >(position)) { // this seems to go in ruby sass 3.4.20
            error("Import directives may not be used within control directives or mixins.");
          }
        }
        // this puts the parsed doc into sheets
        // import stub will fetch this in expand
        Import_Obj imp = parse_import();
        // if it is a url, we only add the statement
        if (!imp->urls().empty()) block->append(imp);
        // process all resources now (add Import_Stub nodes)
        for (size_t i = 0, S = imp->incs().size(); i < S; ++i) {
          block->append(SASS_MEMORY_NEW(Import_Stub, pstate, imp->incs()[i]));
        }
      }
  
      else if (lex < kwd_extend >(true)) {
        Lookahead lookahead = lookahead_for_include(position);
        if (!lookahead.found) css_error("Invalid CSS", " after ", ": expected selector, was ");
        SelectorListObj target;
        if (!lookahead.has_interpolants) {
          LOCAL_FLAG(allow_parent, false);
          auto selector = parseSelectorList(true);
          auto extender = SASS_MEMORY_NEW(ExtendRule, pstate, selector);
          extender->isOptional(selector && selector->is_optional());
          block->append(extender);
        }
        else {
          LOCAL_FLAG(allow_parent, false);
          auto selector = parse_selector_schema(lookahead.found, true);
          auto extender = SASS_MEMORY_NEW(ExtendRule, pstate, selector);
          // A schema is not optional yet, check once it is evaluated
          // extender->isOptional(selector && selector->is_optional());
          block->append(extender);
        }
  
      }
  
      // selector may contain interpolations which need delayed evaluation
      else if (
        !(lookahead_result = lookahead_for_selector(position)).error &&
        !lookahead_result.is_custom_property
      )
      {
        block->append(parse_ruleset(lookahead_result));
      }
  
      // parse multiple specific keyword directives
      else if (lex < kwd_media >(true)) { block->append(parseMediaRule()); }
      else if (lex < kwd_at_root >(true)) { block->append(parse_at_root_block()); }
      else if (lex < kwd_include_directive >(true)) { block->append(parse_include_directive()); }
      else if (lex < kwd_content_directive >(true)) { block->append(parse_content_directive()); }
      else if (lex < kwd_supports_directive >(true)) { block->append(parse_supports_directive()); }
      else if (lex < kwd_mixin >(true)) { block->append(parse_definition(Definition::MIXIN)); }
      else if (lex < kwd_function >(true)) { block->append(parse_definition(Definition::FUNCTION)); }
  
      // ignore the @charset directive for now
      else if (lex< kwd_charset_directive >(true)) { parse_charset_directive(); }
  
      else if (lex < exactly < else_kwd >>(true)) { error("Invalid CSS: @else must come after @if"); }
  
      // generic at keyword (keep last)
      else if (lex< at_keyword >(true)) { block->append(parse_directive()); }
  
      else if (is_root && stack.back() != Scope::AtRoot /* && block->is_root() */) {
        lex< css_whitespace >();
        if (position >= end) return true;
        css_error("Invalid CSS", " after ", ": expected 1 selector or at-rule, was ");
      }
      // parse a declaration
      else
      {
        // ToDo: how does it handle parse errors?
        // maybe we are expected to parse something?
        Declaration_Obj decl = parse_declaration();
        decl->tabs(indentation);
        block->append(decl);
        // maybe we have a "sub-block"
        if (peek< exactly<'{'> >()) {
          if (decl->is_indented()) ++ indentation;
          // parse a propset that rides on the declaration's property
          stack.push_back(Scope::Properties);
          decl->block(parse_block());
          stack.pop_back();
          if (decl->is_indented()) -- indentation;
        }
      }
      // something matched
      return true;
    }
    // EO parse_block_nodes
  
    // parse imports inside the
    Import_Obj Parser::parse_import()
    {
      Import_Obj imp = SASS_MEMORY_NEW(Import, pstate);
      std::vector<std::pair<std::string,Function_Call_Obj>> to_import;
      bool first = true;
      do {
        while (lex< block_comment >());
        if (lex< quoted_string >()) {
          to_import.push_back(std::pair<std::string,Function_Call_Obj>(std::string(lexed), {}));
        }
        else if (lex< uri_prefix >()) {
          Arguments_Obj args = SASS_MEMORY_NEW(Arguments, pstate);
          Function_Call_Obj result = SASS_MEMORY_NEW(Function_Call, pstate, std::string("url"), args);
  
          if (lex< quoted_string >()) {
            Expression_Obj quoted_url = parse_string();
            args->append(SASS_MEMORY_NEW(Argument, quoted_url->pstate(), quoted_url));
          }
          else if (String_Obj string_url = parse_url_function_argument()) {
            args->append(SASS_MEMORY_NEW(Argument, string_url->pstate(), string_url));
          }
          else if (peek < skip_over_scopes < exactly < '(' >, exactly < ')' > > >(position)) {
            Expression_Obj braced_url = parse_list(); // parse_interpolated_chunk(lexed);
            args->append(SASS_MEMORY_NEW(Argument, braced_url->pstate(), braced_url));
          }
          else {
            error("malformed URL");
          }
          if (!lex< exactly<')'> >()) error("URI is missing ')'");
          to_import.push_back(std::pair<std::string, Function_Call_Obj>("", result));
        }
        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_css< exactly<','> >());
  
      if (!peek_css< alternatives< exactly<';'>, exactly<'}'>, end_of_file > >()) {
        List_Obj import_queries = parse_media_queries();
        imp->import_queries(import_queries);
      }
  
      for(auto location : to_import) {
        if (location.second) {
          imp->urls().push_back(location.second);
        }
        // check if custom importers want to take over the handling
        else if (!ctx.call_importers(unquote(location.first), path, pstate, imp)) {
          // nobody wants it, so we do our import
          ctx.import_url(imp, location.first, path);
        }
      }
  
      return imp;
    }
  
    Definition_Obj Parser::parse_definition(Definition::Type which_type)
    {
      std::string which_str(lexed);
      if (!lex< identifier >()) error("invalid name in " + which_str + " definition");
      std::string name(Util::normalize_underscores(lexed));
      if (which_type == Definition::FUNCTION && (name == "and" || name == "or" || name == "not"))
      { error("Invalid function name \"" + name + "\"."); }
      ParserState source_position_of_def = pstate;
      Parameters_Obj params = parse_parameters();
      if (which_type == Definition::MIXIN) stack.push_back(Scope::Mixin);
      else stack.push_back(Scope::Function);
      Block_Obj body = parse_block();
      stack.pop_back();
      return SASS_MEMORY_NEW(Definition, source_position_of_def, name, params, body, which_type);
    }
  
    Parameters_Obj Parser::parse_parameters()
    {
      Parameters_Obj params = SASS_MEMORY_NEW(Parameters, pstate);
      if (lex_css< exactly<'('> >()) {
        // if there's anything there at all
        if (!peek_css< exactly<')'> >()) {
          do {
            if (peek< exactly<')'> >()) break;
            params->append(parse_parameter());
          } while (lex_css< exactly<','> >());
        }
        if (!lex_css< exactly<')'> >()) {
          css_error("Invalid CSS", " after ", ": expected \")\", was ");
        }
      }
      return params;
    }
  
    Parameter_Obj Parser::parse_parameter()
    {
      if (peek< alternatives< exactly<','>, exactly< '{' >, exactly<';'> > >()) {
        css_error("Invalid CSS", " after ", ": expected variable (e.g. $foo), was ");
      }
      while (lex< alternatives < spaces, block_comment > >());
      lex < variable >();
      std::string name(Util::normalize_underscores(lexed));
      ParserState pos = pstate;
      Expression_Obj val;
      bool is_rest = false;
      while (lex< alternatives < spaces, block_comment > >());
      if (lex< exactly<':'> >()) { // there's a default value
        while (lex< block_comment >());
        val = parse_space_list();
      }
      else if (lex< exactly< ellipsis > >()) {
        is_rest = true;
      }
      return SASS_MEMORY_NEW(Parameter, pos, name, val, is_rest);
    }
  
    Arguments_Obj Parser::parse_arguments()
    {
      Arguments_Obj args = SASS_MEMORY_NEW(Arguments, pstate);
      if (lex_css< exactly<'('> >()) {
        // if there's anything there at all
        if (!peek_css< exactly<')'> >()) {
          do {
            if (peek< exactly<')'> >()) break;
            args->append(parse_argument());
          } while (lex_css< exactly<','> >());
        }
        if (!lex_css< exactly<')'> >()) {
          css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
        }
      }
      return args;
    }
  
    Argument_Obj Parser::parse_argument()
    {
      if (peek< alternatives< exactly<','>, exactly< '{' >, exactly<';'> > >()) {
        css_error("Invalid CSS", " after ", ": expected \")\", was ");
      }
      if (peek_css< sequence < exactly< hash_lbrace >, exactly< rbrace > > >()) {
        position += 2;
        css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
      }
  
      Argument_Obj arg;
      if (peek_css< sequence < variable, optional_css_comments, exactly<':'> > >()) {
        lex_css< variable >();
        std::string name(Util::normalize_underscores(lexed));
        ParserState p = pstate;
        lex_css< exactly<':'> >();
        Expression_Obj val = parse_space_list();
        arg = SASS_MEMORY_NEW(Argument, p, val, name);
      }
      else {
        bool is_arglist = false;
        bool is_keyword = false;
        Expression_Obj val = parse_space_list();
        List* l = Cast<List>(val);
        if (lex_css< exactly< ellipsis > >()) {
          if (val->concrete_type() == Expression::MAP || (
             (l != NULL && l->separator() == SASS_HASH)
          )) is_keyword = true;
          else is_arglist = true;
        }
        arg = SASS_MEMORY_NEW(Argument, pstate, val, "", is_arglist, is_keyword);
      }
      return arg;
    }
  
    Assignment_Obj Parser::parse_assignment()
    {
      std::string name(Util::normalize_underscores(lexed));
      ParserState var_source_position = pstate;
      if (!lex< exactly<':'> >()) error("expected ':' after " + name + " in assignment statement");
      if (peek_css< alternatives < exactly<';'>, end_of_file > >()) {
        css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
      }
      Expression_Obj val;
      Lookahead lookahead = lookahead_for_value(position);
      if (lookahead.has_interpolants && lookahead.found) {
        val = parse_value_schema(lookahead.found);
      } else {
        val = parse_list();
      }
      bool is_default = false;
      bool is_global = false;
      while (peek< alternatives < default_flag, global_flag > >()) {
        if (lex< default_flag >()) is_default = true;
        else if (lex< global_flag >()) is_global = true;
      }
      return SASS_MEMORY_NEW(Assignment, var_source_position, name, val, is_default, is_global);
    }
  
    // a ruleset connects a selector and a block
    Ruleset_Obj Parser::parse_ruleset(Lookahead lookahead)
    {
      NESTING_GUARD(nestings);
      // inherit is_root from parent block
      Block_Obj parent = block_stack.back();
      bool is_root = parent && parent->is_root();
      // make sure to move up the the last position
      lex < optional_css_whitespace >(false, true);
      // create the connector object (add parts later)
      Ruleset_Obj ruleset = SASS_MEMORY_NEW(Ruleset, pstate);
      // parse selector static or as schema to be evaluated later
      if (lookahead.parsable) {
        ruleset->selector(parseSelectorList(false));
      }
      else {
        SelectorListObj list = SASS_MEMORY_NEW(SelectorList, pstate);
        auto sc = parse_selector_schema(lookahead.position, false);
        ruleset->schema(sc);
        ruleset->selector(list);
      }
      // then parse the inner block
      stack.push_back(Scope::Rules);
      ruleset->block(parse_block());
      stack.pop_back();
      // update for end position
      ruleset->update_pstate(pstate);
      ruleset->block()->update_pstate(pstate);
      // need this info for sanity checks
      ruleset->is_root(is_root);
      // return AST Node
      return ruleset;
    }
  
    // parse a selector schema that will be evaluated in the eval stage
    // uses a string schema internally to do the actual schema handling
    // in the eval stage we will be re-parse it into an actual selector
    Selector_Schema_Obj Parser::parse_selector_schema(const char* end_of_selector, bool chroot)
    {
      NESTING_GUARD(nestings);
      // move up to the start
      lex< optional_spaces >();
      const char* i = position;
      // selector schema re-uses string schema implementation
      String_Schema* schema = SASS_MEMORY_NEW(String_Schema, pstate);
      // the selector schema is pretty much just a wrapper for the string schema
      Selector_Schema_Obj selector_schema = SASS_MEMORY_NEW(Selector_Schema, pstate, schema);
      selector_schema->connect_parent(chroot == false);
  
      // process until end
      while (i < end_of_selector) {
        // try to parse multiple interpolants
        if (const char* p = find_first_in_interval< exactly<hash_lbrace>, block_comment >(i, end_of_selector)) {
          // accumulate the preceding segment if the position has advanced
          if (i < p) {
            std::string parsed(i, p);
            String_Constant_Obj str = SASS_MEMORY_NEW(String_Constant, pstate, parsed);
            pstate += Offset(parsed);
            str->update_pstate(pstate);
            schema->append(str);
          }
  
          // skip over all nested inner interpolations up to our own delimiter
          const char* j = skip_over_scopes< exactly<hash_lbrace>, exactly<rbrace> >(p + 2, end_of_selector);
          // check if the interpolation never ends of only contains white-space (error out)
          if (!j || peek < sequence < optional_spaces, exactly<rbrace> > >(p+2)) {
            position = p+2;
            css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
          }
          // pass inner expression to the parser to resolve nested interpolations
          pstate.add(p, p+2);
          Expression_Obj interpolant = Parser::from_c_str(p+2, j, ctx, traces, pstate).parse_list();
          // set status on the list expression
          interpolant->is_interpolant(true);
          // schema->has_interpolants(true);
          // add to the string schema
          schema->append(interpolant);
          // advance parser state
          pstate.add(p+2, j);
          // advance position
          i = j;
        }
        // no more interpolants have been found
        // add the last segment if there is one
        else {
          // make sure to add the last bits of the string up to the end (if any)
          if (i < end_of_selector) {
            std::string parsed(i, end_of_selector);
            String_Constant_Obj str = SASS_MEMORY_NEW(String_Constant, pstate, parsed);
            pstate += Offset(parsed);
            str->update_pstate(pstate);
            i = end_of_selector;
            schema->append(str);
          }
          // exit loop
        }
      }
      // EO until eos
  
      // update position
      position = i;
  
      // update for end position
      selector_schema->update_pstate(pstate);
      schema->update_pstate(pstate);
  
      after_token = before_token = pstate;
  
      // return parsed result
      return selector_schema.detach();
    }
    // EO parse_selector_schema
  
    void Parser::parse_charset_directive()
    {
      lex <
        sequence <
          quoted_string,
          optional_spaces,
          exactly <';'>
        >
      >();
    }
  
    // called after parsing `kwd_include_directive`
    Mixin_Call_Obj Parser::parse_include_directive()
    {
      // lex identifier into `lexed` var
      lex_identifier(); // may error out
      // normalize underscores to hyphens
      std::string name(Util::normalize_underscores(lexed));
      // create the initial mixin call object
      Mixin_Call_Obj call = SASS_MEMORY_NEW(Mixin_Call, pstate, name, {}, {}, {});
      // parse mandatory arguments
      call->arguments(parse_arguments());
      // parse using and optional block parameters
      bool has_parameters = lex< kwd_using >() != nullptr;
  
      if (has_parameters) {
        if (!peek< exactly<'('> >()) css_error("Invalid CSS", " after ", ": expected \"(\", was ");
      } else {
        if (peek< exactly<'('> >()) css_error("Invalid CSS", " after ", ": expected \";\", was ");
      }
  
      if (has_parameters) call->block_parameters(parse_parameters());
  
      // parse optional block
      if (peek < exactly <'{'> >()) {
        call->block(parse_block());
      }
      else if (has_parameters)  {
        css_error("Invalid CSS", " after ", ": expected \"{\", was ");
      }
      // return ast node
      return call.detach();
    }
    // EO parse_include_directive
  
  
    SimpleSelectorObj Parser::parse_simple_selector()
    {
      lex < css_comments >(false);
      if (lex< class_name >()) {
        return SASS_MEMORY_NEW(Class_Selector, pstate, lexed);
      }
      else if (lex< id_name >()) {
        return SASS_MEMORY_NEW(Id_Selector, pstate, lexed);
      }
      else if (lex< alternatives < variable, number, static_reference_combinator > >()) {
        return SASS_MEMORY_NEW(Type_Selector, pstate, lexed);
      }
      else if (peek< pseudo_not >()) {
        return parse_negated_selector2();
      }
      else if (peek< re_pseudo_selector >()) {
        return parse_pseudo_selector();
      }
      else if (peek< exactly<':'> >()) {
        return parse_pseudo_selector();
      }
      else if (lex < exactly<'['> >()) {
        return parse_attribute_selector();
      }
      else if (lex< placeholder >()) {
        return SASS_MEMORY_NEW(Placeholder_Selector, pstate, lexed);
      }
      else {
        css_error("Invalid CSS", " after ", ": expected selector, was ");
      }
      // failed
      return {};
    }
  
    Pseudo_Selector_Obj Parser::parse_negated_selector2()
    {
      lex< pseudo_not >();
      std::string name(lexed);
      ParserState nsource_position = pstate;
      SelectorListObj negated = parseSelectorList(true);
      if (!lex< exactly<')'> >()) {
        error("negated selector is missing ')'");
      }
      name.erase(name.size() - 1);
  
      Pseudo_Selector* sel = SASS_MEMORY_NEW(Pseudo_Selector, nsource_position, name.substr(1));
      sel->selector(negated);
      return sel;
    }
  
    // Helper to clean binominal string
    bool BothAreSpaces(char lhs, char rhs) { return isspace(lhs) && isspace(rhs); }
  
    // a pseudo selector often starts with one or two colons
    // it can contain more selectors inside parentheses
    SimpleSelectorObj Parser::parse_pseudo_selector() {
  
      // Lex one or two colon characters
      if (lex<pseudo_prefix>()) {
        std::string colons(lexed);
        // Check if it is a pseudo element
        bool element = colons.size() == 2;
  
        if (lex< sequence<
          // we keep the space within the name, strange enough
          // ToDo: refactor output to schedule the space for it
          // or do we really want to keep the real white-space?
          sequence< identifier, optional < block_comment >, exactly<'('> >
        > >())
        {
  
          std::string name(lexed);
          name.erase(name.size() - 1);
          ParserState p = pstate;
  
          // specially parse nth-child pseudo selectors
          if (lex_css < sequence < binomial, word_boundary >>()) {
            std::string parsed(lexed); // always compacting binominals (as dart-sass)
            parsed.erase(std::unique(parsed.begin(), parsed.end(), BothAreSpaces), parsed.end());
            String_Constant_Obj arg = SASS_MEMORY_NEW(String_Constant, pstate, parsed);
            Pseudo_Selector* pseudo = SASS_MEMORY_NEW(Pseudo_Selector, p, name, element);
            if (lex < sequence < css_whitespace, insensitive < of_kwd >>>(false)) {
              pseudo->selector(parseSelectorList(true));
            }
            pseudo->argument(arg);
            if (lex_css< exactly<')'> >()) {
              return pseudo;
            }
          }
          else {
            if (peek_css< exactly<')'>>()  && Util::equalsLiteral("nth-", name.substr(0, 4))) {
              css_error("Invalid CSS", " after ", ": expected An+B expression, was ");
            }
  
            std::string unvendored = Util::unvendor(name);
  
            if (unvendored == "not" || unvendored == "matches" || unvendored == "current"  || unvendored == "any" || unvendored == "has" || unvendored == "host" || unvendored == "host-context" || unvendored == "slotted") {
               if (SelectorListObj wrapped = parseSelectorList(true)) {
                  if (wrapped && lex_css< exactly<')'> >()) {
                    Pseudo_Selector* pseudo = SASS_MEMORY_NEW(Pseudo_Selector, p, name, element);
                    pseudo->selector(wrapped);
                    return pseudo;
                  }
                }
            } else {
              String_Schema_Obj arg = parse_css_variable_value();
              Pseudo_Selector* pseudo = SASS_MEMORY_NEW(Pseudo_Selector, p, name, element);
              pseudo->argument(arg);
  
              if (lex_css< exactly<')'> >()) {
                return pseudo;
              }
            }
          }
  
        }
        // EO if pseudo selector
  
        else if (lex < sequence< optional < pseudo_prefix >, identifier > >()) {
          return SASS_MEMORY_NEW(Pseudo_Selector, pstate, lexed, element);
        }
        else if (lex < pseudo_prefix >()) {
          css_error("Invalid CSS", " after ", ": expected pseudoclass or pseudoelement, was ");
        }
  
      }
      else {
        lex < identifier >(); // needed for error message?
        css_error("Invalid CSS", " after ", ": expected selector, was ");
      }
  
  
      css_error("Invalid CSS", " after ", ": expected \")\", was ");
  
      // unreachable statement
      return {};
    }
  
    const char* Parser::re_attr_sensitive_close(const char* src)
    {
      return alternatives < exactly<']'>, exactly<'/'> >(src);
    }
  
    const char* Parser::re_attr_insensitive_close(const char* src)
    {
      return sequence < insensitive<'i'>, re_attr_sensitive_close >(src);
    }
  
    Attribute_Selector_Obj Parser::parse_attribute_selector()
    {
      ParserState p = pstate;
      if (!lex_css< attribute_name >()) error("invalid attribute name in attribute selector");
      std::string name(lexed);
      if (lex_css< re_attr_sensitive_close >()) {
        return SASS_MEMORY_NEW(Attribute_Selector, p, name, "", {}, {});
      }
      else if (lex_css< re_attr_insensitive_close >()) {
        char modifier = lexed.begin[0];
        return SASS_MEMORY_NEW(Attribute_Selector, p, name, "", {}, modifier);
      }
      if (!lex_css< alternatives< exact_match, class_match, dash_match,
                                  prefix_match, suffix_match, substring_match > >()) {
        error("invalid operator in attribute selector for " + name);
      }
      std::string matcher(lexed);
  
      String_Obj value;
      if (lex_css< identifier >()) {
        value = SASS_MEMORY_NEW(String_Constant, p, lexed);
      }
      else if (lex_css< quoted_string >()) {
        value = parse_interpolated_chunk(lexed, true); // needed!
      }
      else {
        error("expected a string constant or identifier in attribute selector for " + name);
      }
  
      if (lex_css< re_attr_sensitive_close >()) {
        return SASS_MEMORY_NEW(Attribute_Selector, p, name, matcher, value, 0);
      }
      else if (lex_css< re_attr_insensitive_close >()) {
        char modifier = lexed.begin[0];
        return SASS_MEMORY_NEW(Attribute_Selector, p, name, matcher, value, modifier);
      }
      error("unterminated attribute selector for " + name);
      return {}; // to satisfy compilers (error must not return)
    }
  
    /* parse block comment and add to block */
    void Parser::parse_block_comments(bool store)
    {
      Block_Obj block = block_stack.back();
  
      while (lex< block_comment >()) {
        bool is_important = lexed.begin[2] == '!';
        // flag on second param is to skip loosely over comments
        String_Obj contents = parse_interpolated_chunk(lexed, true, false);
        if (store) block->append(SASS_MEMORY_NEW(Comment, pstate, contents, is_important));
      }
    }
  
    Declaration_Obj Parser::parse_declaration() {
      String_Obj prop;
      bool is_custom_property = false;
      if (lex< sequence< optional< exactly<'*'> >, identifier_schema > >()) {
        const std::string property(lexed);
        is_custom_property = property.compare(0, 2, "--") == 0;
        prop = parse_identifier_schema();
      }
      else if (lex< sequence< optional< exactly<'*'> >, identifier, zero_plus< block_comment > > >()) {
        const std::string property(lexed);
        is_custom_property = property.compare(0, 2, "--") == 0;
        prop = SASS_MEMORY_NEW(String_Constant, pstate, lexed);
      }
      else {
        css_error("Invalid CSS", " after ", ": expected \"}\", was ");
      }
      bool is_indented = true;
      const std::string property(lexed);
      if (!lex_css< one_plus< exactly<':'> > >()) error("property \"" + escape_string(property)  + "\" must be followed by a ':'");
      if (!is_custom_property && match< sequence< optional_css_comments, exactly<';'> > >()) error("style declaration must contain a value");
      if (match< sequence< optional_css_comments, exactly<'{'> > >()) is_indented = false; // don't indent if value is empty
      if (is_custom_property) {
        return SASS_MEMORY_NEW(Declaration, prop->pstate(), prop, parse_css_variable_value(), false, true);
      }
      lex < css_comments >(false);
      if (peek_css< static_value >()) {
        return SASS_MEMORY_NEW(Declaration, prop->pstate(), prop, parse_static_value()/*, lex<kwd_important>()*/);
      }
      else {
        Expression_Obj value;
        Lookahead lookahead = lookahead_for_value(position);
        if (lookahead.found) {
          if (lookahead.has_interpolants) {
            value = parse_value_schema(lookahead.found);
          } else {
            value = parse_list(DELAYED);
          }
        }
        else {
          value = parse_list(DELAYED);
          if (List* list = Cast<List>(value)) {
            if (!list->is_bracketed() && list->length() == 0 && !peek< exactly <'{'> >()) {
              css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
            }
          }
        }
        lex < css_comments >(false);
        Declaration_Obj decl = SASS_MEMORY_NEW(Declaration, prop->pstate(), prop, value/*, lex<kwd_important>()*/);
        decl->is_indented(is_indented);
        decl->update_pstate(pstate);
        return decl;
      }
    }
  
    Expression_Obj Parser::parse_map()
    {
      NESTING_GUARD(nestings);
      Expression_Obj key = parse_list();
      List_Obj map = SASS_MEMORY_NEW(List, pstate, 0, SASS_HASH);
  
      // it's not a map so return the lexed value as a list value
      if (!lex_css< exactly<':'> >())
      { return key; }
  
      List_Obj l = Cast<List>(key);
      if (l && l->separator() == SASS_COMMA) {
        css_error("Invalid CSS", " after ", ": expected \")\", was ");
      }
  
      Expression_Obj value = parse_space_list();
  
      map->append(key);
      map->append(value);
  
      while (lex_css< exactly<','> >())
      {
        // allow trailing commas - #495
        if (peek_css< exactly<')'> >(position))
        { break; }
  
        key = parse_space_list();
  
        if (!(lex< exactly<':'> >()))
        { css_error("Invalid CSS", " after ", ": expected \":\", was "); }
  
        value = parse_space_list();
  
        map->append(key);
        map->append(value);
      }
  
      ParserState ps = map->pstate();
      ps.offset = pstate - ps + pstate.offset;
      map->pstate(ps);
  
      return map;
    }
  
    Expression_Obj Parser::parse_bracket_list()
    {
      NESTING_GUARD(nestings);
      // check if we have an empty list
      // return the empty list as such
      if (peek_css< list_terminator >(position))
      {
        // return an empty list (nothing to delay)
        return SASS_MEMORY_NEW(List, pstate, 0, SASS_SPACE, false, true);
      }
  
      bool has_paren = peek_css< exactly<'('> >() != NULL;
  
      // now try to parse a space list
      Expression_Obj list = parse_space_list();
      // if it's a singleton, return it (don't wrap it)
      if (!peek_css< exactly<','> >(position)) {
        List_Obj l = Cast<List>(list);
        if (!l || l->is_bracketed() || has_paren) {
          List_Obj bracketed_list = SASS_MEMORY_NEW(List, pstate, 1, SASS_SPACE, false, true);
          bracketed_list->append(list);
          return bracketed_list;
        }
        l->is_bracketed(true);
        return l;
      }
  
      // if we got so far, we actually do have a comma list
      List_Obj bracketed_list = SASS_MEMORY_NEW(List, pstate, 2, SASS_COMMA, false, true);
      // wrap the first expression
      bracketed_list->append(list);
  
      while (lex_css< exactly<','> >())
      {
        // check for abort condition
        if (peek_css< list_terminator >(position)
        ) { break; }
        // otherwise add another expression
        bracketed_list->append(parse_space_list());
      }
      // return the list
      return bracketed_list;
    }
  
    // parse list returns either a space separated list,
    // a comma separated list or any bare expression found.
    // so to speak: we unwrap items from lists if possible here!
    Expression_Obj Parser::parse_list(bool delayed)
    {
      NESTING_GUARD(nestings);
      return parse_comma_list(delayed);
    }
  
    // will return singletons unwrapped
    Expression_Obj Parser::parse_comma_list(bool delayed)
    {
      NESTING_GUARD(nestings);
      // check if we have an empty list
      // return the empty list as such
      if (peek_css< list_terminator >(position))
      {
        // return an empty list (nothing to delay)
        return SASS_MEMORY_NEW(List, pstate, 0);
      }
  
      // now try to parse a space list
      Expression_Obj list = parse_space_list();
      // if it's a singleton, return it (don't wrap it)
      if (!peek_css< exactly<','> >(position)) {
        // set_delay doesn't apply to list children
        // so this will only undelay single values
        if (!delayed) list->set_delayed(false);
        return list;
      }
  
      // if we got so far, we actually do have a comma list
      List_Obj comma_list = SASS_MEMORY_NEW(List, pstate, 2, SASS_COMMA);
      // wrap the first expression
      comma_list->append(list);
  
      while (lex_css< exactly<','> >())
      {
        // check for abort condition
        if (peek_css< list_terminator >(position)
        ) { break; }
        // otherwise add another expression
        comma_list->append(parse_space_list());
      }
      // return the list
      return comma_list;
    }
    // EO parse_comma_list
  
    // will return singletons unwrapped
    Expression_Obj Parser::parse_space_list()
    {
      NESTING_GUARD(nestings);
      Expression_Obj disj1 = parse_disjunction();
      // if it's a singleton, return it (don't wrap it)
      if (peek_css< space_list_terminator >(position)
      ) {
        return disj1; }
  
      List_Obj space_list = SASS_MEMORY_NEW(List, pstate, 2, SASS_SPACE);
      space_list->append(disj1);
  
      while (
        !(peek_css< space_list_terminator >(position)) &&
        peek_css< optional_css_whitespace >() != end
      ) {
        // the space is parsed implicitly?
        space_list->append(parse_disjunction());
      }
      // return the list
      return space_list;
    }
    // EO parse_space_list
  
    // parse logical OR operation
    Expression_Obj Parser::parse_disjunction()
    {
      NESTING_GUARD(nestings);
      advanceToNextToken();
      ParserState state(pstate);
      // parse the left hand side conjunction
      Expression_Obj conj = parse_conjunction();
      // parse multiple right hand sides
      std::vector<Expression_Obj> operands;
      while (lex_css< kwd_or >())
        operands.push_back(parse_conjunction());
      // if it's a singleton, return it directly
      if (operands.size() == 0) return conj;
      // fold all operands into one binary expression
      Expression_Obj ex = fold_operands(conj, operands, { Sass_OP::OR });
      state.offset = pstate - state + pstate.offset;
      ex->pstate(state);
      return ex;
    }
    // EO parse_disjunction
  
    // parse logical AND operation
    Expression_Obj Parser::parse_conjunction()
    {
      NESTING_GUARD(nestings);
      advanceToNextToken();
      ParserState state(pstate);
      // parse the left hand side relation
      Expression_Obj rel = parse_relation();
      // parse multiple right hand sides
      std::vector<Expression_Obj> operands;
      while (lex_css< kwd_and >()) {
        operands.push_back(parse_relation());
      }
      // if it's a singleton, return it directly
      if (operands.size() == 0) return rel;
      // fold all operands into one binary expression
      Expression_Obj ex = fold_operands(rel, operands, { Sass_OP::AND });
      state.offset = pstate - state + pstate.offset;
      ex->pstate(state);
      return ex;
    }
    // EO parse_conjunction
  
    // parse comparison operations
    Expression_Obj Parser::parse_relation()
    {
      NESTING_GUARD(nestings);
      advanceToNextToken();
      ParserState state(pstate);
      // parse the left hand side expression
      Expression_Obj lhs = parse_expression();
      std::vector<Expression_Obj> operands;
      std::vector<Operand> operators;
      // if it's a singleton, return it (don't wrap it)
      while (peek< alternatives <
              kwd_eq,
              kwd_neq,
              kwd_gte,
              kwd_gt,
              kwd_lte,
              kwd_lt
            > >(position))
      {
        // is directly adjancent to expression?
        bool left_ws = peek < css_comments >() != NULL;
        // parse the operator
        enum Sass_OP op
        = lex<kwd_eq>()  ? Sass_OP::EQ
        : lex<kwd_neq>() ? Sass_OP::NEQ
        : lex<kwd_gte>() ? Sass_OP::GTE
        : lex<kwd_lte>() ? Sass_OP::LTE
        : lex<kwd_gt>()  ? Sass_OP::GT
        : lex<kwd_lt>()  ? Sass_OP::LT
        // we checked the possibilities on top of fn
        :                  Sass_OP::EQ;
        // is directly adjacent to expression?
        bool right_ws = peek < css_comments >() != NULL;
        operators.push_back({ op, left_ws, right_ws });
        operands.push_back(parse_expression());
      }
      // we are called recursively for list, so we first
      // fold inner binary expression which has delayed
      // correctly set to zero. After folding we also unwrap
      // single nested items. So we cannot set delay on the
      // returned result here, as we have lost nestings ...
      Expression_Obj ex = fold_operands(lhs, operands, operators);
      state.offset = pstate - state + pstate.offset;
      ex->pstate(state);
      return ex;
    }
    // parse_relation
  
    // parse expression valid for operations
    // called from parse_relation
    // called from parse_for_directive
    // called from parse_media_expression
    // parse addition and subtraction operations
    Expression_Obj Parser::parse_expression()
    {
      NESTING_GUARD(nestings);
      advanceToNextToken();
      ParserState state(pstate);
      // parses multiple add and subtract operations
      // NOTE: make sure that identifiers starting with
      // NOTE: dashes do NOT count as subtract operation
      Expression_Obj lhs = parse_operators();
      // if it's a singleton, return it (don't wrap it)
      if (!(peek_css< exactly<'+'> >(position) ||
            // condition is a bit mysterious, but some combinations should not be counted as operations
            (peek< no_spaces >(position) && peek< sequence< negate< unsigned_number >, exactly<'-'>, negate< space > > >(position)) ||
            (peek< sequence< negate< unsigned_number >, exactly<'-'>, negate< unsigned_number > > >(position))) ||
            peek< sequence < zero_plus < exactly <'-' > >, identifier > >(position))
      { return lhs; }
  
      std::vector<Expression_Obj> operands;
      std::vector<Operand> operators;
      bool left_ws = peek < css_comments >() != NULL;
      while (
        lex_css< exactly<'+'> >() ||
  
        (
        ! peek_css< sequence < zero_plus < exactly <'-' > >, identifier > >(position)
        && lex_css< sequence< negate< digit >, exactly<'-'> > >()
        )
  
      ) {
  
        bool right_ws = peek < css_comments >() != NULL;
        operators.push_back({ lexed.to_string() == "+" ? Sass_OP::ADD : Sass_OP::SUB, left_ws, right_ws });
        operands.push_back(parse_operators());
        left_ws = peek < css_comments >() != NULL;
      }
  
      if (operands.size() == 0) return lhs;
      Expression_Obj ex = fold_operands(lhs, operands, operators);
      state.offset = pstate - state + pstate.offset;
      ex->pstate(state);
      return ex;
    }
  
    // parse addition and subtraction operations
    Expression_Obj Parser::parse_operators()
    {
      NESTING_GUARD(nestings);
      advanceToNextToken();
      ParserState state(pstate);
      Expression_Obj factor = parse_factor();
      // if it's a singleton, return it (don't wrap it)
      std::vector<Expression_Obj> operands; // factors
      std::vector<Operand> operators; // ops
      // lex operations to apply to lhs
      const char* left_ws = peek < css_comments >();
      while (lex_css< class_char< static_ops > >()) {
        const char* right_ws = peek < css_comments >();
        switch(*lexed.begin) {
          case '*': operators.push_back({ Sass_OP::MUL, left_ws != 0, right_ws != 0 }); break;
          case '/': operators.push_back({ Sass_OP::DIV, left_ws != 0, right_ws != 0 }); break;
          case '%': operators.push_back({ Sass_OP::MOD, left_ws != 0, right_ws != 0 }); break;
          default: throw std::runtime_error("unknown static op parsed");
        }
        operands.push_back(parse_factor());
        left_ws = peek < css_comments >();
      }
      // operands and operators to binary expression
      Expression_Obj ex = fold_operands(factor, operands, operators);
      state.offset = pstate - state + pstate.offset;
      ex->pstate(state);
      return ex;
    }
    // EO parse_operators
  
  
    // called from parse_operators
    // called from parse_value_schema
    Expression_Obj Parser::parse_factor()
    {
      NESTING_GUARD(nestings);
      lex < css_comments >(false);
      if (lex_css< exactly<'('> >()) {
        // parse_map may return a list
        Expression_Obj value = parse_map();
        // lex the expected closing parenthesis
        if (!lex_css< exactly<')'> >()) error("unclosed parenthesis");
        // expression can be evaluated
        return value;
      }
      else if (lex_css< exactly<'['> >()) {
        // explicit bracketed
        Expression_Obj value = parse_bracket_list();
        // lex the expected closing square bracket
        if (!lex_css< exactly<']'> >()) error("unclosed squared bracket");
        return value;
      }
      // string may be interpolated
      // if (lex< quoted_string >()) {
      //   return &parse_string();
      // }
      else if (peek< ie_property >()) {
        return parse_ie_property();
      }
      else if (peek< ie_keyword_arg >()) {
        return parse_ie_keyword_arg();
      }
      else if (peek< sequence < calc_fn_call, exactly <'('> > >()) {
        return parse_calc_function();
      }
      else if (lex < functional_schema >()) {
        return parse_function_call_schema();
      }
      else if (lex< identifier_schema >()) {
        String_Obj string = parse_identifier_schema();
        if (String_Schema* schema = Cast<String_Schema>(string)) {
          if (lex < exactly < '(' > >()) {
            schema->append(parse_list());
            lex < exactly < ')' > >();
          }
        }
        return string;
      }
      else if (peek< sequence< uri_prefix, W, real_uri_value > >()) {
        return parse_url_function_string();
      }
      else if (peek< re_functional >()) {
        return parse_function_call();
      }
      else if (lex< exactly<'+'> >()) {
        Unary_Expression* ex = SASS_MEMORY_NEW(Unary_Expression, pstate, Unary_Expression::PLUS, parse_factor());
        if (ex && ex->operand()) ex->is_delayed(ex->operand()->is_delayed());
        return ex;
      }
      else if (lex< exactly<'-'> >()) {
        Unary_Expression* ex = SASS_MEMORY_NEW(Unary_Expression, pstate, Unary_Expression::MINUS, parse_factor());
        if (ex && ex->operand()) ex->is_delayed(ex->operand()->is_delayed());
        return ex;
      }
      else if (lex< exactly<'/'> >()) {
        Unary_Expression* ex = SASS_MEMORY_NEW(Unary_Expression, pstate, Unary_Expression::SLASH, parse_factor());
        if (ex && ex->operand()) ex->is_delayed(ex->operand()->is_delayed());
        return ex;
      }
      else if (lex< sequence< kwd_not > >()) {
        Unary_Expression* ex = SASS_MEMORY_NEW(Unary_Expression, pstate, Unary_Expression::NOT, parse_factor());
        if (ex && ex->operand()) ex->is_delayed(ex->operand()->is_delayed());
        return ex;
      }
      else {
        return parse_value();
      }
    }
  
    bool number_has_zero(const std::string& parsed)
    {
      size_t L = parsed.length();
      return !( (L > 0 && parsed.substr(0, 1) == ".") ||
                (L > 1 && parsed.substr(0, 2) == "0.") ||
                (L > 1 && parsed.substr(0, 2) == "-.")  ||
                (L > 2 && parsed.substr(0, 3) == "-0.") );
    }
  
    Number* Parser::lexed_number(const ParserState& pstate, const std::string& parsed)
    {
      Number* nr = SASS_MEMORY_NEW(Number,
                                      pstate,
                                      sass_strtod(parsed.c_str()),
                                      "",
                                      number_has_zero(parsed));
      nr->is_interpolant(false);
      nr->is_delayed(true);
      return nr;
    }
  
    Number* Parser::lexed_percentage(const ParserState& pstate, const std::string& parsed)
    {
      Number* nr = SASS_MEMORY_NEW(Number,
                                      pstate,
                                      sass_strtod(parsed.c_str()),
                                      "%",
                                      true);
      nr->is_interpolant(false);
      nr->is_delayed(true);
      return nr;
    }
  
    Number* Parser::lexed_dimension(const ParserState& pstate, const std::string& parsed)
    {
      size_t L = parsed.length();
      size_t num_pos = parsed.find_first_not_of(" \n\r\t");
      if (num_pos == std::string::npos) num_pos = L;
      size_t unit_pos = parsed.find_first_not_of("-+0123456789.", num_pos);
      if (parsed[unit_pos] == 'e' && is_number(parsed[unit_pos+1]) ) {
        unit_pos = parsed.find_first_not_of("-+0123456789.", ++ unit_pos);
      }
      if (unit_pos == std::string::npos) unit_pos = L;
      const std::string& num = parsed.substr(num_pos, unit_pos - num_pos);
      Number* nr = SASS_MEMORY_NEW(Number,
                                      pstate,
                                      sass_strtod(num.c_str()),
                                      Token(number(parsed.c_str())),
                                      number_has_zero(parsed));
      nr->is_interpolant(false);
      nr->is_delayed(true);
      return nr;
    }
  
    Value* Parser::lexed_hex_color(const ParserState& pstate, const std::string& parsed)
    {
      Color_RGBA* color = NULL;
      if (parsed[0] != '#') {
        return SASS_MEMORY_NEW(String_Quoted, pstate, parsed);
      }
      // chop off the '#'
      std::string hext(parsed.substr(1));
      if (parsed.length() == 4) {
        std::string r(2, parsed[1]);
        std::string g(2, parsed[2]);
        std::string b(2, parsed[3]);
        color = SASS_MEMORY_NEW(Color_RGBA,
                                 pstate,
                                 static_cast<double>(strtol(r.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(g.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(b.c_str(), NULL, 16)),
                                 1, // alpha channel
                                 parsed);
      }
      else if (parsed.length() == 5) {
        std::string r(2, parsed[1]);
        std::string g(2, parsed[2]);
        std::string b(2, parsed[3]);
        std::string a(2, parsed[4]);
        color = SASS_MEMORY_NEW(Color_RGBA,
                                 pstate,
                                 static_cast<double>(strtol(r.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(g.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(b.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(a.c_str(), NULL, 16)) / 255,
                                 parsed);
      }
      else if (parsed.length() == 7) {
        std::string r(parsed.substr(1,2));
        std::string g(parsed.substr(3,2));
        std::string b(parsed.substr(5,2));
        color = SASS_MEMORY_NEW(Color_RGBA,
                                 pstate,
                                 static_cast<double>(strtol(r.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(g.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(b.c_str(), NULL, 16)),
                                 1, // alpha channel
                                 parsed);
      }
      else if (parsed.length() == 9) {
        std::string r(parsed.substr(1,2));
        std::string g(parsed.substr(3,2));
        std::string b(parsed.substr(5,2));
        std::string a(parsed.substr(7,2));
        color = SASS_MEMORY_NEW(Color_RGBA,
                                 pstate,
                                 static_cast<double>(strtol(r.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(g.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(b.c_str(), NULL, 16)),
                                 static_cast<double>(strtol(a.c_str(), NULL, 16)) / 255,
                                 parsed);
      }
      color->is_interpolant(false);
      color->is_delayed(false);
      return color;
    }
  
    Value* Parser::color_or_string(const std::string& lexed) const
    {
      if (auto color = name_to_color(lexed)) {
        auto c = SASS_MEMORY_NEW(Color_RGBA, color);
        c->is_delayed(true);
        c->pstate(pstate);
        c->disp(lexed);
        return c;
      } else {
        return SASS_MEMORY_NEW(String_Constant, pstate, lexed);
      }
    }
  
    // parse one value for a list
    Expression_Obj Parser::parse_value()
    {
      lex< css_comments >(false);
      if (lex< ampersand >())
      {
        if (match< ampersand >()) {
          warning("In Sass, \"&&\" means two copies of the parent selector. You probably want to use \"and\" instead.", pstate);
        }
        return SASS_MEMORY_NEW(Parent_Reference, pstate); }
  
      if (lex< kwd_important >())
      { return SASS_MEMORY_NEW(String_Constant, pstate, "!important"); }
  
      // parse `10%4px` into separated items and not a schema
      if (lex< sequence < percentage, lookahead < number > > >())
      { return lexed_percentage(lexed); }
  
      if (lex< sequence < number, lookahead< sequence < op, number > > > >())
      { return lexed_number(lexed); }
  
      // string may be interpolated
      if (lex< sequence < quoted_string, lookahead < exactly <'-'> > > >())
      { return parse_string(); }
  
      if (const char* stop = peek< value_schema >())
      { return parse_value_schema(stop); }
  
      // string may be interpolated
      if (lex< quoted_string >())
      { return parse_string(); }
  
      if (lex< kwd_true >())
      { return SASS_MEMORY_NEW(Boolean, pstate, true); }
  
      if (lex< kwd_false >())
      { return SASS_MEMORY_NEW(Boolean, pstate, false); }
  
      if (lex< kwd_null >())
      { return SASS_MEMORY_NEW(Null, pstate); }
  
      if (lex< identifier >()) {
        return color_or_string(lexed);
      }
  
      if (lex< percentage >())
      { return lexed_percentage(lexed); }
  
      // match hex number first because 0x000 looks like a number followed by an identifier
      if (lex< sequence < alternatives< hex, hex0 >, negate < exactly<'-'> > > >())
      { return lexed_hex_color(lexed); }
  
      if (lex< hexa >())
      { return lexed_hex_color(lexed); }
  
      if (lex< sequence < exactly <'#'>, identifier > >())
      { return SASS_MEMORY_NEW(String_Quoted, pstate, lexed); }
  
      // also handle the 10em- foo special case
      // alternatives < exactly < '.' >, .. > -- `1.5em-.75em` is split into a list, not a binary expression
      if (lex< sequence< dimension, optional< sequence< exactly<'-'>, lookahead< alternatives < space > > > > > >())
      { return lexed_dimension(lexed); }
  
      if (lex< sequence< static_component, one_plus< strict_identifier > > >())
      { return SASS_MEMORY_NEW(String_Constant, pstate, lexed); }
  
      if (lex< number >())
      { return lexed_number(lexed); }
  
      if (lex< variable >())
      { return SASS_MEMORY_NEW(Variable, pstate, Util::normalize_underscores(lexed)); }
  
      css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
  
      // unreachable statement
      return {};
    }
  
    // this parses interpolation inside other strings
    // means the result should later be quoted again
    String_Obj Parser::parse_interpolated_chunk(Token chunk, bool constant, bool css)
    {
      const char* i = chunk.begin;
      // see if there any interpolants
      const char* p = constant ? find_first_in_interval< exactly<hash_lbrace> >(i, chunk.end) :
                      find_first_in_interval< exactly<hash_lbrace>, block_comment >(i, chunk.end);
  
      if (!p) {
        String_Quoted* str_quoted = SASS_MEMORY_NEW(String_Quoted, pstate, std::string(i, chunk.end), 0, false, false, true, css);
        if (!constant && str_quoted->quote_mark()) str_quoted->quote_mark('*');
        return str_quoted;
      }
  
      String_Schema_Obj schema = SASS_MEMORY_NEW(String_Schema, pstate, 0, css);
      schema->is_interpolant(true);
      while (i < chunk.end) {
        p = constant ? find_first_in_interval< exactly<hash_lbrace> >(i, chunk.end) :
            find_first_in_interval< exactly<hash_lbrace>, block_comment >(i, chunk.end);
        if (p) {
          if (i < p) {
            // accumulate the preceding segment if it's nonempty
            schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(i, p), css));
          }
          // we need to skip anything inside strings
          // create a new target in parser/prelexer
          if (peek < sequence < optional_spaces, exactly<rbrace> > >(p+2)) { position = p+2;
            css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
          }
          const char* j = skip_over_scopes< exactly<hash_lbrace>, exactly<rbrace> >(p + 2, chunk.end); // find the closing brace
          if (j) { --j;
            // parse the interpolant and accumulate it
            Expression_Obj interp_node = Parser::from_token(Token(p+2, j), ctx, traces, pstate, source).parse_list();
            interp_node->is_interpolant(true);
            schema->append(interp_node);
            i = j;
          }
          else {
            // throw an error if the interpolant is unterminated
            error("unterminated interpolant inside string constant " + chunk.to_string());
          }
        }
        else { // no interpolants left; add the last segment if nonempty
          // check if we need quotes here (was not sure after merge)
          if (i < chunk.end) schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(i, chunk.end), css));
          break;
        }
        ++ i;
      }
  
      return schema.detach();
    }
  
    String_Schema_Obj Parser::parse_css_variable_value()
    {
      String_Schema_Obj schema = SASS_MEMORY_NEW(String_Schema, pstate);
      std::vector<char> brackets;
      while (true) {
        if (
          (brackets.empty() && lex< css_variable_top_level_value >(false)) ||
          (!brackets.empty() && lex< css_variable_value >(false))
        ) {
          Token str(lexed);
          schema->append(SASS_MEMORY_NEW(String_Constant, pstate, str));
        } else if (Expression_Obj tok = lex_interpolation()) {
          if (String_Schema* s = Cast<String_Schema>(tok)) {
            if (s->empty()) break;
            schema->concat(s);
          } else {
            schema->append(tok);
          }
        } else if (lex< quoted_string >()) {
          Expression_Obj tok = parse_string();
          if (tok.isNull()) break;
          if (String_Schema* s = Cast<String_Schema>(tok)) {
            if (s->empty()) break;
            schema->concat(s);
          } else {
            schema->append(tok);
          }
        } else if (lex< alternatives< exactly<'('>, exactly<'['>, exactly<'{'> > >()) {
          const char opening_bracket = *(position - 1);
          brackets.push_back(opening_bracket);
          schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(1, opening_bracket)));
        } else if (const char *match = peek< alternatives< exactly<')'>, exactly<']'>, exactly<'}'> > >()) {
          if (brackets.empty()) break;
          const char closing_bracket = *(match - 1);
          if (brackets.back() != Util::opening_bracket_for(closing_bracket)) {
            std::string message = ": expected \"";
            message += Util::closing_bracket_for(brackets.back());
            message += "\", was ";
            css_error("Invalid CSS", " after ", message);
          }
          lex< alternatives< exactly<')'>, exactly<']'>, exactly<'}'> > >();
          schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(1, closing_bracket)));
          brackets.pop_back();
        } else {
          break;
        }
      }
  
      if (!brackets.empty()) {
        std::string message = ": expected \"";
        message += Util::closing_bracket_for(brackets.back());
        message += "\", was ";
        css_error("Invalid CSS", " after ", message);
      }
  
      if (schema->empty()) error("Custom property values may not be empty.");
      return schema.detach();
    }
  
    Value_Obj Parser::parse_static_value()
    {
      lex< static_value >();
      Token str(lexed);
      // static values always have trailing white-
      // space and end delimiter (\s*[;]$) included
      --pstate.offset.column;
      --after_token.column;
      --str.end;
      --position;
  
      return color_or_string(str.time_wspace());;
    }
  
    String_Obj Parser::parse_string()
    {
      return parse_interpolated_chunk(Token(lexed));
    }
  
    String_Obj Parser::parse_ie_property()
    {
      lex< ie_property >();
      Token str(lexed);
      const char* i = str.begin;
      // see if there any interpolants
      const char* p = find_first_in_interval< exactly<hash_lbrace>, block_comment >(str.begin, str.end);
      if (!p) {
        return SASS_MEMORY_NEW(String_Quoted, pstate, std::string(str.begin, str.end));
      }
  
      String_Schema* schema = SASS_MEMORY_NEW(String_Schema, pstate);
      while (i < str.end) {
        p = find_first_in_interval< exactly<hash_lbrace>, block_comment >(i, str.end);
        if (p) {
          if (i < p) {
            schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(i, p))); // accumulate the preceding segment if it's nonempty
          }
          if (peek < sequence < optional_spaces, exactly<rbrace> > >(p+2)) { position = p+2;
            css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
          }
          const char* j = skip_over_scopes< exactly<hash_lbrace>, exactly<rbrace> >(p+2, str.end); // find the closing brace
          if (j) {
            // parse the interpolant and accumulate it
            Expression_Obj interp_node = Parser::from_token(Token(p+2, j), ctx, traces, pstate, source).parse_list();
            interp_node->is_interpolant(true);
            schema->append(interp_node);
            i = j;
          }
          else {
            // throw an error if the interpolant is unterminated
            error("unterminated interpolant inside IE function " + str.to_string());
          }
        }
        else { // no interpolants left; add the last segment if nonempty
          if (i < str.end) {
            schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(i, str.end)));
          }
          break;
        }
      }
      return schema;
    }
  
    String_Obj Parser::parse_ie_keyword_arg()
    {
      String_Schema_Obj kwd_arg = SASS_MEMORY_NEW(String_Schema, pstate, 3);
      if (lex< variable >()) {
        kwd_arg->append(SASS_MEMORY_NEW(Variable, pstate, Util::normalize_underscores(lexed)));
      } else {
        lex< alternatives< identifier_schema, identifier > >();
        kwd_arg->append(SASS_MEMORY_NEW(String_Constant, pstate, lexed));
      }
      lex< exactly<'='> >();
      kwd_arg->append(SASS_MEMORY_NEW(String_Constant, pstate, lexed));
      if (peek< variable >()) kwd_arg->append(parse_list());
      else if (lex< number >()) {
        std::string parsed(lexed);
        Util::normalize_decimals(parsed);
        kwd_arg->append(lexed_number(parsed));
      }
      else if (peek < ie_keyword_arg_value >()) { kwd_arg->append(parse_list()); }
      return kwd_arg;
    }
  
    String_Schema_Obj Parser::parse_value_schema(const char* stop)
    {
      // initialize the string schema object to add tokens
      String_Schema_Obj schema = SASS_MEMORY_NEW(String_Schema, pstate);
  
      if (peek<exactly<'}'>>()) {
        css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
      }
  
      const char* e;
      const char* ee = end;
      end = stop;
      size_t num_items = 0;
      bool need_space = false;
      while (position < stop) {
        // parse space between tokens
        if (lex< spaces >() && num_items) {
          need_space = true;
        }
        if (need_space) {
          need_space = false;
          // schema->append(SASS_MEMORY_NEW(String_Constant, pstate, " "));
        }
        if ((e = peek< re_functional >()) && e < stop) {
          schema->append(parse_function_call());
        }
        // lex an interpolant /#{...}/
        else if (lex< exactly < hash_lbrace > >()) {
          // Try to lex static expression first
          if (peek< exactly< rbrace > >()) {
            css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
          }
          Expression_Obj ex;
          if (lex< re_static_expression >()) {
            ex = SASS_MEMORY_NEW(String_Constant, pstate, lexed);
          } else {
            ex = parse_list(true);
          }
          ex->is_interpolant(true);
          schema->append(ex);
          if (!lex < exactly < rbrace > >()) {
            css_error("Invalid CSS", " after ", ": expected \"}\", was ");
          }
        }
        // lex some string constants or other valid token
        // Note: [-+] chars are left over from i.e. `#{3}+3`
        else if (lex< alternatives < exactly<'%'>, exactly < '-' >, exactly < '+' > > >()) {
          schema->append(SASS_MEMORY_NEW(String_Constant, pstate, lexed));
        }
        // lex a quoted string
        else if (lex< quoted_string >()) {
          // need_space = true;
          // if (schema->length()) schema->append(SASS_MEMORY_NEW(String_Constant, pstate, " "));
          // else need_space = true;
          schema->append(parse_string());
          if ((*position == '"' || *position == '\'') || peek < alternatives < alpha > >()) {
            // need_space = true;
          }
          if (peek < exactly < '-' > >()) break;
        }
        else if (lex< identifier >()) {
          schema->append(SASS_MEMORY_NEW(String_Constant, pstate, lexed));
          if ((*position == '"' || *position == '\'') || peek < alternatives < alpha > >()) {
             // need_space = true;
          }
        }
        // lex (normalized) variable
        else if (lex< variable >()) {
          std::string name(Util::normalize_underscores(lexed));
          schema->append(SASS_MEMORY_NEW(Variable, pstate, name));
        }
        // lex percentage value
        else if (lex< percentage >()) {
          schema->append(lexed_percentage(lexed));
        }
        // lex dimension value
        else if (lex< dimension >()) {
          schema->append(lexed_dimension(lexed));
        }
        // lex number value
        else if (lex< number >()) {
          schema->append(lexed_number(lexed));
        }
        // lex hex color value
        else if (lex< sequence < hex, negate < exactly < '-' > > > >()) {
          schema->append(lexed_hex_color(lexed));
        }
        else if (lex< sequence < exactly <'#'>, identifier > >()) {
          schema->append(SASS_MEMORY_NEW(String_Quoted, pstate, lexed));
        }
        // lex a value in parentheses
        else if (peek< parenthese_scope >()) {
          schema->append(parse_factor());
        }
        else {
          break;
        }
        ++num_items;
      }
      if (position != stop) {
        schema->append(SASS_MEMORY_NEW(String_Constant, pstate, std::string(position, stop)));
        position = stop;
      }
      end = ee;
      return schema;
    }
  
    // this parses interpolation outside other strings
    // means the result must not be quoted again later
    String_Obj Parser::parse_identifier_schema()
    {
      Token id(lexed);
      const char* i = id.begin;
      // see if there any interpolants
      const char* p = find_first_in_interval< exactly<hash_lbrace>, block_comment >(id.begin, id.end);
      if (!p) {
        return SASS_MEMORY_NEW(String_Constant, pstate, std::string(id.begin, id.end));
      }
  
      String_Schema_Obj schema = SASS_MEMORY_NEW(String_Schema, pstate);
      while (i < id.end) {
        p = find_first_in_interval< exactly<hash_lbrace>, block_comment >(i, id.end);
        if (p) {
          if (i < p) {
            // accumulate the preceding segment if it's nonempty
            const char* o = position; position = i;
            schema->append(parse_value_schema(p));
            position = o;
          }
          // we need to skip anything inside strings
          // create a new target in parser/prelexer
          if (peek < sequence < optional_spaces, exactly<rbrace> > >(p+2)) { position = p;
            css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ");
          }
          const char* j = skip_over_scopes< exactly<hash_lbrace>, exactly<rbrace> >(p+2, id.end); // find the closing brace
          if (j) {
            // parse the interpolant and accumulate it
            Expression_Obj interp_node = Parser::from_token(Token(p+2, j), ctx, traces, pstate, source).parse_list(DELAYED);
            interp_node->is_interpolant(true);
            schema->append(interp_node);
            // schema->has_interpolants(true);
            i = j;
          }
          else {
            // throw an error if the interpolant is unterminated
            error("unterminated interpolant inside interpolated identifier " + id.to_string());
          }
        }
        else { // no interpolants left; add the last segment if nonempty
          if (i < end) {
            const char* o = position; position = i;
            schema->append(parse_value_schema(id.end));
            position = o;
          }
          break;
        }
      }
      return schema ? schema.detach() : 0;
    }
  
    // calc functions should preserve arguments
    Function_Call_Obj Parser::parse_calc_function()
    {
      lex< identifier >();
      std::string name(lexed);
      ParserState call_pos = pstate;
      lex< exactly<'('> >();
      ParserState arg_pos = pstate;
      const char* arg_beg = position;
      parse_list();
      const char* arg_end = position;
      lex< skip_over_scopes <
            exactly < '(' >,
            exactly < ')' >
          > >();
  
      Argument_Obj arg = SASS_MEMORY_NEW(Argument, arg_pos, parse_interpolated_chunk(Token(arg_beg, arg_end)));
      Arguments_Obj args = SASS_MEMORY_NEW(Arguments, arg_pos);
      args->append(arg);
      return SASS_MEMORY_NEW(Function_Call, call_pos, name, args);
    }
  
    String_Obj Parser::parse_url_function_string()
    {
      std::string prefix("");
      if (lex< uri_prefix >()) {
        prefix = std::string(lexed);
      }
  
      lex < optional_spaces >();
      String_Obj url_string = parse_url_function_argument();
  
      std::string suffix("");
      if (lex< real_uri_suffix >()) {
        suffix = std::string(lexed);
      }
  
      std::string uri("");
      if (url_string) {
        uri = url_string->to_string({ NESTED, 5 });
      }
  
      if (String_Schema* schema = Cast<String_Schema>(url_string)) {
        String_Schema_Obj res = SASS_MEMORY_NEW(String_Schema, pstate);
        res->append(SASS_MEMORY_NEW(String_Constant, pstate, prefix));
        res->append(schema);
        res->append(SASS_MEMORY_NEW(String_Constant, pstate, suffix));
        return res;
      } else {
        std::string res = prefix + uri + suffix;
        return SASS_MEMORY_NEW(String_Constant, pstate, res);
      }
    }
  
    String_Obj Parser::parse_url_function_argument()
    {
      const char* p = position;
  
      std::string uri("");
      if (lex< real_uri_value >(false)) {
        uri = lexed.to_string();
      }
  
      if (peek< exactly< hash_lbrace > >()) {
        const char* pp = position;
        // TODO: error checking for unclosed interpolants
        while (pp && peek< exactly< hash_lbrace > >(pp)) {
          pp = sequence< interpolant, real_uri_value >(pp);
        }
        if (!pp) return {};
        position = pp;
        return parse_interpolated_chunk(Token(p, position));
      }
      else if (uri != "") {
        std::string res = Util::rtrim(uri);
        return SASS_MEMORY_NEW(String_Constant, pstate, res);
      }
  
      return {};
    }
  
    Function_Call_Obj Parser::parse_function_call()
    {
      lex< identifier >();
      std::string name(lexed);
  
      if (Util::normalize_underscores(name) == "content-exists" && stack.back() != Scope::Mixin)
      { error("Cannot call content-exists() except within a mixin."); }
  
      ParserState call_pos = pstate;
      Arguments_Obj args = parse_arguments();
      return SASS_MEMORY_NEW(Function_Call, call_pos, name, args);
    }
  
    Function_Call_Obj Parser::parse_function_call_schema()
    {
      String_Obj name = parse_identifier_schema();
      ParserState source_position_of_call = pstate;
      Arguments_Obj args = parse_arguments();
  
      return SASS_MEMORY_NEW(Function_Call, source_position_of_call, name, args);
    }
  
    Content_Obj Parser::parse_content_directive()
    {
      ParserState call_pos = pstate;
      Arguments_Obj args = parse_arguments();
  
      return SASS_MEMORY_NEW(Content, call_pos, args);
    }
  
    If_Obj Parser::parse_if_directive(bool else_if)
    {
      stack.push_back(Scope::Control);
      ParserState if_source_position = pstate;
      bool root = block_stack.back()->is_root();
      Expression_Obj predicate = parse_list();
      Block_Obj block = parse_block(root);
      Block_Obj alternative;
  
      // only throw away comment if we parse a case
      // we want all other comments to be parsed
      if (lex_css< elseif_directive >()) {
        alternative = SASS_MEMORY_NEW(Block, pstate);
        alternative->append(parse_if_directive(true));
      }
      else if (lex_css< kwd_else_directive >()) {
        alternative = parse_block(root);
      }
      stack.pop_back();
      return SASS_MEMORY_NEW(If, if_source_position, predicate, block, alternative);
    }
  
    For_Obj Parser::parse_for_directive()
    {
      stack.push_back(Scope::Control);
      ParserState for_source_position = pstate;
      bool root = block_stack.back()->is_root();
      lex_variable();
      std::string var(Util::normalize_underscores(lexed));
      if (!lex< kwd_from >()) error("expected 'from' keyword in @for directive");
      Expression_Obj lower_bound = parse_expression();
      bool inclusive = false;
      if (lex< kwd_through >()) inclusive = true;
      else if (lex< kwd_to >()) inclusive = false;
      else                  error("expected 'through' or 'to' keyword in @for directive");
      Expression_Obj upper_bound = parse_expression();
      Block_Obj body = parse_block(root);
      stack.pop_back();
      return SASS_MEMORY_NEW(For, for_source_position, var, lower_bound, upper_bound, body, inclusive);
    }
  
    // helper to parse a var token
    Token Parser::lex_variable()
    {
      // peek for dollar sign first
      if (!peek< exactly <'$'> >()) {
        css_error("Invalid CSS", " after ", ": expected \"$\", was ");
      }
      // we expect a simple identifier as the call name
      if (!lex< sequence < exactly <'$'>, identifier > >()) {
        lex< exactly <'$'> >(); // move pstate and position up
        css_error("Invalid CSS", " after ", ": expected identifier, was ");
      }
      // return object
      return token;
    }
    // helper to parse identifier
    Token Parser::lex_identifier()
    {
      // we expect a simple identifier as the call name
      if (!lex< identifier >()) { // ToDo: pstate wrong?
        css_error("Invalid CSS", " after ", ": expected identifier, was ");
      }
      // return object
      return token;
    }
  
    Each_Obj Parser::parse_each_directive()
    {
      stack.push_back(Scope::Control);
      ParserState each_source_position = pstate;
      bool root = block_stack.back()->is_root();
      std::vector<std::string> vars;
      lex_variable();
      vars.push_back(Util::normalize_underscores(lexed));
      while (lex< exactly<','> >()) {
        if (!lex< variable >()) error("@each directive requires an iteration variable");
        vars.push_back(Util::normalize_underscores(lexed));
      }
      if (!lex< kwd_in >()) error("expected 'in' keyword in @each directive");
      Expression_Obj list = parse_list();
      Block_Obj body = parse_block(root);
      stack.pop_back();
      return SASS_MEMORY_NEW(Each, each_source_position, vars, list, body);
    }
  
    // called after parsing `kwd_while_directive`
    While_Obj Parser::parse_while_directive()
    {
      stack.push_back(Scope::Control);
      bool root = block_stack.back()->is_root();
      // create the initial while call object
      While_Obj call = SASS_MEMORY_NEW(While, pstate, {}, {});
      // parse mandatory predicate
      Expression_Obj predicate = parse_list();
      List_Obj l = Cast<List>(predicate);
      if (!predicate || (l && !l->length())) {
        css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was ", false);
      }
      call->predicate(predicate);
      // parse mandatory block
      call->block(parse_block(root));
      // return ast node
      stack.pop_back();
      // return ast node
      return call.detach();
    }
  
  
    std::vector<CssMediaQuery_Obj> Parser::parseCssMediaQueries()
    {
      std::vector<CssMediaQuery_Obj> result;
      do {
        if (auto query = parseCssMediaQuery()) {
          result.push_back(query);
        }
      } while (lex<exactly<','>>());
      return result;
    }
  
    std::string Parser::parseIdentifier()
    {
      if (lex < identifier >(false)) {
        return std::string(lexed);
      }
      return std::string();
    }
  
    CssMediaQuery_Obj Parser::parseCssMediaQuery()
    {
      CssMediaQuery_Obj result = SASS_MEMORY_NEW(CssMediaQuery, pstate);
      lex<css_comments>(false);
  
      // Check if any tokens are to parse
      if (!peek_css<exactly<'('>>()) {
  
        std::string token1(parseIdentifier());
        lex<css_comments>(false);
  
        if (token1.empty()) {
          return {};
        }
  
        std::string token2(parseIdentifier());
        lex<css_comments>(false);
  
        if (Util::equalsLiteral("and", token2)) {
          result->type(token1);
        }
        else {
          if (token2.empty()) {
            result->type(token1);
          }
          else {
            result->modifier(token1);
            result->type(token2);
          }
  
          if (lex < kwd_and >()) {
            lex<css_comments>(false);
          }
          else {
            return result;
          }
  
        }
  
      }
  
      std::vector<std::string> queries;
  
      do {
        lex<css_comments>(false);
  
        if (lex<exactly<'('>>()) {
          // In dart sass parser returns a pure string
          if (lex < skip_over_scopes < exactly < '(' >, exactly < ')' > > >()) {
            std::string decl("(" + std::string(lexed));
            queries.push_back(decl);
          }
          // Should be: parseDeclarationValue;
          if (!lex<exactly<')'>>()) {
            // Should we throw an error here?
          }
        }
      } while (lex < kwd_and >());
  
      result->features(queries);
  
      if (result->features().empty()) {
        if (result->type().empty()) {
          return {};
        }
      }
  
      return result;
    }
  
  
    // EO parse_while_directive
    MediaRule_Obj Parser::parseMediaRule()
    {
      MediaRule_Obj rule = SASS_MEMORY_NEW(MediaRule, pstate);
      stack.push_back(Scope::Media);
      rule->schema(parse_media_queries());
      parse_block_comments(false);
      rule->block(parse_css_block());
      stack.pop_back();
      return rule;
    }
  
    List_Obj Parser::parse_media_queries()
    {
      advanceToNextToken();
      List_Obj queries = SASS_MEMORY_NEW(List, pstate, 0, SASS_COMMA);
      if (!peek_css < exactly <'{'> >()) queries->append(parse_media_query());
      while (lex_css < exactly <','> >()) queries->append(parse_media_query());
      queries->update_pstate(pstate);
      return queries.detach();
    }
  
    // Expression* Parser::parse_media_query()
    Media_Query_Obj Parser::parse_media_query()
    {
      advanceToNextToken();
      Media_Query_Obj media_query = SASS_MEMORY_NEW(Media_Query, pstate);
      if (lex < kwd_not >()) { media_query->is_negated(true); lex < css_comments >(false); }
      else if (lex < kwd_only >()) { media_query->is_restricted(true); lex < css_comments >(false); }
  
      if (lex < identifier_schema >())  media_query->media_type(parse_identifier_schema());
      else if (lex < identifier >())    media_query->media_type(parse_interpolated_chunk(lexed));
      else                             media_query->append(parse_media_expression());
  
      while (lex_css < kwd_and >()) media_query->append(parse_media_expression());
      if (lex < identifier_schema >()) {
        String_Schema* schema = SASS_MEMORY_NEW(String_Schema, pstate);
        schema->append(media_query->media_type());
        schema->append(SASS_MEMORY_NEW(String_Constant, pstate, " "));
        schema->append(parse_identifier_schema());
        media_query->media_type(schema);
      }
      while (lex_css < kwd_and >()) media_query->append(parse_media_expression());
  
      media_query->update_pstate(pstate);
  
      return media_query;
    }
  
    Media_Query_Expression_Obj Parser::parse_media_expression()
    {
      if (lex < identifier_schema >()) {
        String_Obj ss = parse_identifier_schema();
        return SASS_MEMORY_NEW(Media_Query_Expression, pstate, ss, {}, true);
      }
      if (!lex_css< exactly<'('> >()) {
        error("media query expression must begin with '('");
      }
      Expression_Obj feature;
      if (peek_css< exactly<')'> >()) {
        error("media feature required in media query expression");
      }
      feature = parse_expression();
      Expression_Obj expression;
      if (lex_css< exactly<':'> >()) {
        expression = parse_list(DELAYED);
      }
      if (!lex_css< exactly<')'> >()) {
        error("unclosed parenthesis in media query expression");
      }
      return SASS_MEMORY_NEW(Media_Query_Expression, feature->pstate(), feature, expression);
    }
  
    // lexed after `kwd_supports_directive`
    // these are very similar to media blocks
    Supports_Block_Obj Parser::parse_supports_directive()
    {
      Supports_Condition_Obj cond = parse_supports_condition(/*top_level=*/true);
      // create the ast node object for the support queries
      Supports_Block_Obj query = SASS_MEMORY_NEW(Supports_Block, pstate, cond);
      // additional block is mandatory
      // parse inner block
      query->block(parse_block());
      // return ast node
      return query;
    }
  
    // parse one query operation
    // may encounter nested queries
    Supports_Condition_Obj Parser::parse_supports_condition(bool top_level)
    {
      lex < css_whitespace >();
      Supports_Condition_Obj cond;
      if ((cond = parse_supports_negation())) return cond;
      if ((cond = parse_supports_operator(top_level))) return cond;
      if ((cond = parse_supports_interpolation())) return cond;
      return cond;
    }
  
    Supports_Condition_Obj Parser::parse_supports_negation()
    {
      if (!lex < kwd_not >()) return {};
      Supports_Condition_Obj cond = parse_supports_condition_in_parens(/*parens_required=*/true);
      return SASS_MEMORY_NEW(Supports_Negation, pstate, cond);
    }
  
    Supports_Condition_Obj Parser::parse_supports_operator(bool top_level)
    {
      Supports_Condition_Obj cond = parse_supports_condition_in_parens(/*parens_required=*/top_level);
      if (cond.isNull()) return {};
  
      while (true) {
        Supports_Operator::Operand op = Supports_Operator::OR;
        if (lex < kwd_and >()) { op = Supports_Operator::AND; }
        else if(!lex < kwd_or >()) { break; }
  
        lex < css_whitespace >();
        Supports_Condition_Obj right = parse_supports_condition_in_parens(/*parens_required=*/true);
  
        // Supports_Condition* cc = SASS_MEMORY_NEW(Supports_Condition, *static_cast<Supports_Condition*>(cond));
        cond = SASS_MEMORY_NEW(Supports_Operator, pstate, cond, right, op);
      }
      return cond;
    }
  
    Supports_Condition_Obj Parser::parse_supports_interpolation()
    {
      if (!lex < interpolant >()) return {};
  
      String_Obj interp = parse_interpolated_chunk(lexed);
      if (!interp) return {};
  
      return SASS_MEMORY_NEW(Supports_Interpolation, pstate, interp);
    }
  
    // TODO: This needs some major work. Although feature conditions
    // look like declarations their semantics differ significantly
    Supports_Condition_Obj Parser::parse_supports_declaration()
    {
      Supports_Condition* cond;
      // parse something declaration like
      Expression_Obj feature = parse_expression();
      Expression_Obj expression;
      if (lex_css< exactly<':'> >()) {
        expression = parse_list(DELAYED);
      }
      if (!feature || !expression) error("@supports condition expected declaration");
      cond = SASS_MEMORY_NEW(Supports_Declaration,
                       feature->pstate(),
                       feature,
                       expression);
      // ToDo: maybe we need an additional error condition?
      return cond;
    }
  
    Supports_Condition_Obj Parser::parse_supports_condition_in_parens(bool parens_required)
    {
      Supports_Condition_Obj interp = parse_supports_interpolation();
      if (interp != nullptr) return interp;
  
      if (!lex < exactly <'('> >()) {
        if (parens_required) {
          css_error("Invalid CSS", " after ", ": expected @supports condition (e.g. (display: flexbox)), was ", /*trim=*/false);
        } else {
          return {};
        }
      }
      lex < css_whitespace >();
  
      Supports_Condition_Obj cond = parse_supports_condition(/*top_level=*/false);
      if (cond.isNull()) cond = parse_supports_declaration();
      if (!lex < exactly <')'> >()) error("unclosed parenthesis in @supports declaration");
  
      lex < css_whitespace >();
      return cond;
    }
  
    At_Root_Block_Obj Parser::parse_at_root_block()
    {
      stack.push_back(Scope::AtRoot);
      ParserState at_source_position = pstate;
      Block_Obj body;
      At_Root_Query_Obj expr;
      Lookahead lookahead_result;
      if (lex_css< exactly<'('> >()) {
        expr = parse_at_root_query();
      }
      if (peek_css < exactly<'{'> >()) {
        lex <optional_spaces>();
        body = parse_block(true);
      }
      else if ((lookahead_result = lookahead_for_selector(position)).found) {
        Ruleset_Obj r = parse_ruleset(lookahead_result);
        body = SASS_MEMORY_NEW(Block, r->pstate(), 1, true);
        body->append(r);
      }
      At_Root_Block_Obj at_root = SASS_MEMORY_NEW(At_Root_Block, at_source_position, body);
      if (!expr.isNull()) at_root->expression(expr);
      stack.pop_back();
      return at_root;
    }
  
    At_Root_Query_Obj Parser::parse_at_root_query()
    {
      if (peek< exactly<')'> >()) error("at-root feature required in at-root expression");
  
      if (!peek< alternatives< kwd_with_directive, kwd_without_directive > >()) {
        css_error("Invalid CSS", " after ", ": expected \"with\" or \"without\", was ");
      }
  
      Expression_Obj feature = parse_list();
      if (!lex_css< exactly<':'> >()) error("style declaration must contain a value");
      Expression_Obj expression = parse_list();
      List_Obj value = SASS_MEMORY_NEW(List, feature->pstate(), 1);
  
      if (expression->concrete_type() == Expression::LIST) {
          value = Cast<List>(expression);
      }
      else value->append(expression);
  
      At_Root_Query_Obj cond = SASS_MEMORY_NEW(At_Root_Query,
                                            value->pstate(),
                                            feature,
                                            value);
      if (!lex_css< exactly<')'> >()) error("unclosed parenthesis in @at-root expression");
      return cond;
    }
  
    Directive_Obj Parser::parse_directive()
    {
      Directive_Obj directive = SASS_MEMORY_NEW(Directive, pstate, lexed);
      String_Schema_Obj val = parse_almost_any_value();
      // strip left and right if they are of type string
      directive->value(val);
      if (peek< exactly<'{'> >()) {
        directive->block(parse_block());
      }
      return directive;
    }
  
    Expression_Obj Parser::lex_interpolation()
    {
      if (lex < interpolant >(true) != NULL) {
        return parse_interpolated_chunk(lexed, true);
      }
      return {};
    }
  
    Expression_Obj Parser::lex_interp_uri()
    {
      // create a string schema by lexing optional interpolations
      return lex_interp< re_string_uri_open, re_string_uri_close >();
    }
  
    Expression_Obj Parser::lex_interp_string()
    {
      Expression_Obj rv;
      if ((rv = lex_interp< re_string_double_open, re_string_double_close >())) return rv;
      if ((rv = lex_interp< re_string_single_open, re_string_single_close >())) return rv;
      return rv;
    }
  
    Expression_Obj Parser::lex_almost_any_value_chars()
    {
      const char* match =
      lex <
        one_plus <
          alternatives <
            exactly <'>'>,
            sequence <
              exactly <'\\'>,
              any_char
            >,
            sequence <
              negate <
                sequence <
                  exactly < url_kwd >,
                  exactly <'('>
                >
              >,
              neg_class_char <
                almost_any_value_class
              >
            >,
            sequence <
              exactly <'/'>,
              negate <
                alternatives <
                  exactly <'/'>,
                  exactly <'*'>
                >
              >
            >,
            sequence <
              exactly <'\\'>,
              exactly <'#'>,
              negate <
                exactly <'{'>
              >
            >,
            sequence <
              exactly <'!'>,
              negate <
                alpha
              >
            >
          >
        >
      >(false);
      if (match) {
        return SASS_MEMORY_NEW(String_Constant, pstate, lexed);
      }
      return {};
    }
  
    Expression_Obj Parser::lex_almost_any_value_token()
    {
      Expression_Obj rv;
      if (*position == 0) return {};
      if ((rv = lex_almost_any_value_chars())) return rv;
      // if ((rv = lex_block_comment())) return rv;
      // if ((rv = lex_single_line_comment())) return rv;
      if ((rv = lex_interp_string())) return rv;
      if ((rv = lex_interp_uri())) return rv;
      if ((rv = lex_interpolation())) return rv;
       if (lex< alternatives< hex, hex0 > >())
      { return lexed_hex_color(lexed); }
     return rv;
    }
  
    String_Schema_Obj Parser::parse_almost_any_value()
    {
  
      String_Schema_Obj schema = SASS_MEMORY_NEW(String_Schema, pstate);
      if (*position == 0) return {};
      lex < spaces >(false);
      Expression_Obj token = lex_almost_any_value_token();
      if (!token) return {};
      schema->append(token);
      if (*position == 0) {
        schema->rtrim();
        return schema.detach();
      }
  
      while ((token = lex_almost_any_value_token())) {
        schema->append(token);
      }
  
      lex < css_whitespace >();
  
      schema->rtrim();
  
      return schema.detach();
    }
  
    Warning_Obj Parser::parse_warning()
    {
      if (stack.back() != Scope::Root &&
          stack.back() != Scope::Function &&
          stack.back() != Scope::Mixin &&
          stack.back() != Scope::Control &&
          stack.back() != Scope::Rules) {
        error("Illegal nesting: Only properties may be nested beneath properties.");
      }
      return SASS_MEMORY_NEW(Warning, pstate, parse_list(DELAYED));
    }
  
    Error_Obj Parser::parse_error()
    {
      if (stack.back() != Scope::Root &&
          stack.back() != Scope::Function &&
          stack.back() != Scope::Mixin &&
          stack.back() != Scope::Control &&
          stack.back() != Scope::Rules) {
        error("Illegal nesting: Only properties may be nested beneath properties.");
      }
      return SASS_MEMORY_NEW(Error, pstate, parse_list(DELAYED));
    }
  
    Debug_Obj Parser::parse_debug()
    {
      if (stack.back() != Scope::Root &&
          stack.back() != Scope::Function &&
          stack.back() != Scope::Mixin &&
          stack.back() != Scope::Control &&
          stack.back() != Scope::Rules) {
        error("Illegal nesting: Only properties may be nested beneath properties.");
      }
      return SASS_MEMORY_NEW(Debug, pstate, parse_list(DELAYED));
    }
  
    Return_Obj Parser::parse_return_directive()
    {
      // check that we do not have an empty list (ToDo: check if we got all cases)
      if (peek_css < alternatives < exactly < ';' >, exactly < '}' >, end_of_file > >())
      { css_error("Invalid CSS", " after ", ": expected expression (e.g. 1px, bold), was "); }
      return SASS_MEMORY_NEW(Return, pstate, parse_list());
    }
  
    Lookahead Parser::lookahead_for_selector(const char* start)
    {
      // init result struct
      Lookahead rv = Lookahead();
      // get start position
      const char* p = start ? start : position;
      // match in one big "regex"
      rv.error = p;
      if (const char* q =
        peek <
          re_selector_list
        >(p)
      ) {
        bool could_be_property = peek< sequence< exactly<'-'>, exactly<'-'> > >(p) != 0;
        bool could_be_escaped = false;
        while (p < q) {
          // did we have interpolations?
          if (*p == '#' && *(p+1) == '{') {
            rv.has_interpolants = true;
            p = q; break;
          }
          // A property that's ambiguous with a nested selector is interpreted as a
          // custom property.
          if (*p == ':' && !could_be_escaped) {
            rv.is_custom_property = could_be_property || p+1 == q || peek< space >(p+1);
          }
          could_be_escaped = *p == '\\';
          ++ p;
        }
        // store anyway  }
  
  
        // ToDo: remove
        rv.error = q;
        rv.position = q;
        // check expected opening bracket
        // only after successful matching
        if (peek < exactly<'{'> >(q)) rv.found = q;
        // else if (peek < end_of_file >(q)) rv.found = q;
        else if (peek < exactly<'('> >(q)) rv.found = q;
        // else if (peek < exactly<';'> >(q)) rv.found = q;
        // else if (peek < exactly<'}'> >(q)) rv.found = q;
        if (rv.found || *p == 0) rv.error = 0;
      }
  
      rv.parsable = ! rv.has_interpolants;
  
      // return result
      return rv;
  
    }
    // EO lookahead_for_selector
  
    // used in parse_block_nodes and parse_special_directive
    // ToDo: actual usage is still not really clear to me?
    Lookahead Parser::lookahead_for_include(const char* start)
    {
      // we actually just lookahead for a selector
      Lookahead rv = lookahead_for_selector(start);
      // but the "found" rules are different
      if (const char* p = rv.position) {
        // check for additional abort condition
        if (peek < exactly<';'> >(p)) rv.found = p;
        else if (peek < exactly<'}'> >(p)) rv.found = p;
      }
      // return result
      return rv;
    }
    // EO lookahead_for_include
  
    // look ahead for a token with interpolation in it
    // we mostly use the result if there is an interpolation
    // everything that passes here gets parsed as one schema
    // meaning it will not be parsed as a space separated list
    Lookahead Parser::lookahead_for_value(const char* start)
    {
      // init result struct
      Lookahead rv = Lookahead();
      // get start position
      const char* p = start ? start : position;
      // match in one big "regex"
      if (const char* q =
        peek <
          non_greedy <
            alternatives <
              // consume whitespace
              block_comment, // spaces,
              // main tokens
              sequence <
                interpolant,
                optional <
                  quoted_string
                >
              >,
              identifier,
              variable,
              // issue #442
              sequence <
                parenthese_scope,
                interpolant,
                optional <
                  quoted_string
                >
              >
            >,
            sequence <
              // optional_spaces,
              alternatives <
                // end_of_file,
                exactly<'{'>,
                exactly<'}'>,
                exactly<';'>
              >
            >
          >
        >(p)
      ) {
        if (p == q) return rv;
        while (p < q) {
          // did we have interpolations?
          if (*p == '#' && *(p+1) == '{') {
            rv.has_interpolants = true;
            p = q; break;
          }
          ++ p;
        }
        // store anyway
        // ToDo: remove
        rv.position = q;
        // check expected opening bracket
        // only after successful matching
        if (peek < exactly<'{'> >(q)) rv.found = q;
        else if (peek < exactly<';'> >(q)) rv.found = q;
        else if (peek < exactly<'}'> >(q)) rv.found = q;
      }
  
      // return result
      return rv;
    }
    // EO lookahead_for_value
  
    void Parser::read_bom()
    {
      size_t skip = 0;
      std::string encoding;
      bool utf_8 = false;
      switch ((unsigned char) source[0]) {
      case 0xEF:
        skip = check_bom_chars(source, end, utf_8_bom, 3);
        encoding = "UTF-8";
        utf_8 = true;
        break;
      case 0xFE:
        skip = check_bom_chars(source, end, utf_16_bom_be, 2);
        encoding = "UTF-16 (big endian)";
        break;
      case 0xFF:
        skip = check_bom_chars(source, end, utf_16_bom_le, 2);
        skip += (skip ? check_bom_chars(source, end, 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, end, utf_32_bom_be, 4);
        encoding = "UTF-32 (big endian)";
        break;
      case 0x2B:
        skip = check_bom_chars(source, end, utf_7_bom_1, 4)
             | check_bom_chars(source, end, utf_7_bom_2, 4)
             | check_bom_chars(source, end, utf_7_bom_3, 4)
             | check_bom_chars(source, end, utf_7_bom_4, 4)
             | check_bom_chars(source, end, utf_7_bom_5, 5);
        encoding = "UTF-7";
        break;
      case 0xF7:
        skip = check_bom_chars(source, end, utf_1_bom, 3);
        encoding = "UTF-1";
        break;
      case 0xDD:
        skip = check_bom_chars(source, end, utf_ebcdic_bom, 4);
        encoding = "UTF-EBCDIC";
        break;
      case 0x0E:
        skip = check_bom_chars(source, end, scsu_bom, 3);
        encoding = "SCSU";
        break;
      case 0xFB:
        skip = check_bom_chars(source, end, bocu_1_bom, 3);
        encoding = "BOCU-1";
        break;
      case 0x84:
        skip = check_bom_chars(source, end, gb_18030_bom, 4);
        encoding = "GB-18030";
        break;
      default: 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 char *end, const unsigned char* bom, size_t len)
    {
      size_t skip = 0;
      if (src + len > end) return 0;
      for (size_t i = 0; i < len; ++i, ++skip) {
        if ((unsigned char) src[i] != bom[i]) return 0;
      }
      return skip;
    }
  
  
    Expression_Obj Parser::fold_operands(Expression_Obj base, std::vector<Expression_Obj>& operands, Operand op)
    {
      for (size_t i = 0, S = operands.size(); i < S; ++i) {
        base = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), op, base, operands[i]);
      }
      return base;
    }
  
    Expression_Obj Parser::fold_operands(Expression_Obj base, std::vector<Expression_Obj>& operands, std::vector<Operand>& ops, size_t i)
    {
      if (String_Schema* schema = Cast<String_Schema>(base)) {
        // return schema;
        if (schema->has_interpolants()) {
          if (i + 1 < operands.size() && (
               (ops[0].operand == Sass_OP::EQ)
            || (ops[0].operand == Sass_OP::ADD)
            || (ops[0].operand == Sass_OP::DIV)
            || (ops[0].operand == Sass_OP::MUL)
            || (ops[0].operand == Sass_OP::NEQ)
            || (ops[0].operand == Sass_OP::LT)
            || (ops[0].operand == Sass_OP::GT)
            || (ops[0].operand == Sass_OP::LTE)
            || (ops[0].operand == Sass_OP::GTE)
          )) {
            Expression_Obj rhs = fold_operands(operands[i], operands, ops, i + 1);
            rhs = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), ops[0], schema, rhs);
            return rhs;
          }
          // return schema;
        }
      }
  
      for (size_t S = operands.size(); i < S; ++i) {
        if (String_Schema* schema = Cast<String_Schema>(operands[i])) {
          if (schema->has_interpolants()) {
            if (i + 1 < S) {
              // this whole branch is never hit via spec tests
              Expression_Obj rhs = fold_operands(operands[i+1], operands, ops, i + 2);
              rhs = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), ops[i], schema, rhs);
              base = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), ops[i], base, rhs);
              return base;
            }
            base = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), ops[i], base, operands[i]);
            return base;
          } else {
            base = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), ops[i], base, operands[i]);
          }
        } else {
          base = SASS_MEMORY_NEW(Binary_Expression, base->pstate(), ops[i], base, operands[i]);
        }
        Binary_Expression* b = Cast<Binary_Expression>(base.ptr());
        if (b && ops[i].operand == Sass_OP::DIV && b->left()->is_delayed() && b->right()->is_delayed()) {
          base->is_delayed(true);
        }
      }
      // nested binary expression are never to be delayed
      if (Binary_Expression* b = Cast<Binary_Expression>(base)) {
        if (Cast<Binary_Expression>(b->left())) base->set_delayed(false);
        if (Cast<Binary_Expression>(b->right())) base->set_delayed(false);
      }
      return base;
    }
  
    void Parser::error(std::string msg, Position pos)
    {
      Position p(pos.line ? pos : before_token);
      ParserState pstate(path, source, p, Offset(0, 0));
      // `pstate.src` may not outlive stack unwind so we must copy it.
      char *src_copy = sass_copy_c_string(pstate.src);
      pstate.src = src_copy;
      traces.push_back(Backtrace(pstate));
      throw Exception::InvalidSass(pstate, traces, msg, src_copy);
    }
  
    void Parser::error(std::string msg)
    {
      error(msg, pstate);
    }
  
    // print a css parsing error with actual context information from parsed source
    void Parser::css_error(const std::string& msg, const std::string& prefix, const std::string& middle, const bool trim)
    {
      int max_len = 18;
      const char* end = this->end;
      while (*end != 0) ++ end;
      const char* pos = peek < optional_spaces >();
      if (!pos) pos = position;
  
      const char* last_pos(pos);
      if (last_pos > source) {
        utf8::prior(last_pos, source);
      }
      // backup position to last significant char
      while (trim && last_pos > source && last_pos < end) {
        if (!Util::ascii_isspace(static_cast<unsigned char>(*last_pos))) break;
        utf8::prior(last_pos, source);
      }
  
      bool ellipsis_left = false;
      const char* pos_left(last_pos);
      const char* end_left(last_pos);
  
      if (*pos_left) utf8::next(pos_left, end);
      if (*end_left) utf8::next(end_left, end);
      while (pos_left > source) {
        if (utf8::distance(pos_left, end_left) >= max_len) {
          utf8::prior(pos_left, source);
          ellipsis_left = *(pos_left) != '\n' &&
                          *(pos_left) != '\r';
          utf8::next(pos_left, end);
          break;
        }
  
        const char* prev = pos_left;
        utf8::prior(prev, source);
        if (*prev == '\r') break;
        if (*prev == '\n') break;
        pos_left = prev;
      }
      if (pos_left < source) {
        pos_left = source;
      }
  
      bool ellipsis_right = false;
      const char* end_right(pos);
      const char* pos_right(pos);
      while (end_right < end) {
        if (utf8::distance(pos_right, end_right) > max_len) {
          ellipsis_left = *(pos_right) != '\n' &&
                          *(pos_right) != '\r';
          break;
        }
        if (*end_right == '\r') break;
        if (*end_right == '\n') break;
        utf8::next(end_right, end);
      }
      // if (*end_right == 0) end_right ++;
  
      std::string left(pos_left, end_left);
      std::string right(pos_right, end_right);
      size_t left_subpos = left.size() > 15 ? left.size() - 15 : 0;
      size_t right_subpos = right.size() > 15 ? right.size() - 15 : 0;
      if (left_subpos && ellipsis_left) left = ellipsis + left.substr(left_subpos);
      if (right_subpos && ellipsis_right) right = right.substr(right_subpos) + ellipsis;
      // Hotfix when source is null, probably due to interpolation parsing!?
      if (source == NULL || *source == 0) source = pstate.src;
      // now pass new message to the more generic error function
      error(msg + prefix + quote(left) + middle + quote(right));
    }
  
  }
  