yaccsem.pas

Yacc例子代码

{
  Semantic routines for the Yacc parser.


  Copyright (c) 1990-92  Albert Graef <[e-mail]>
  Copyright (C) 1996     Berend de Boer <[e-mail]>

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


$Revision: 2 $
$Modtime: 96-08-01 6:03 $

$History: YACCSEM.PAS $
 * 
 * *****************  Version 2  *****************
 * User: Berend       Date: 96-10-10   Time: 21:16
 * Updated in $/Lex and Yacc/tply
 * Updated for protected mode, windows and Delphi 1.X and 2.X.

}


unit YaccSem;

interface


var

act_prec : Integer;
  (* active precedence level in token and precedence declarations (0 in
     %token declaration) *)
act_type : Integer;
  (* active type tag in token, precedence and type declarations *)

procedure yyerror ( msg : String );
  (* YaccLib.yyerror redefined to ignore 'syntax error' message; the parser
     does its own error handling *)

function sym ( k : Integer ) : Integer;
  (* returns internal symbol number for the symbol k; if k is yet undefined,
     a new nonterminal or literal symbol is created, according to the
     appearance of symbol k (nonterminal if an ordinary identifier, literal
     otherwise) *)

function ntsym ( k : Integer ) : Integer;
  (* like sym, but requires symbol k to be a nonterminal symbol; if it
     is already defined a literal, an error message is issued, and a dummy
     nonterminal symbol returned *)

function litsym ( k : Integer; n : Integer ) : Integer;
  (* same for literal symbols; if n>0 it denotes the literal number to be
     assigned to the symbol; when a new literal identifier is defined, a
     corresponding constant definition is also written to the definition
     file *)

procedure next_section;
  (* find next section mark (%%) in code template *)

procedure definitions;
  (* if necessary, write out definition of the semantic value type YYSType *)

procedure copy_code;
  (* copy Turbo Pascal code section ( %{ ... %} ) to output file *)

procedure copy_action;
  (* copy an action to the output file *)

procedure copy_single_action;
  (* like copy_action, but action must be single statement terminated
     with `;' *)

procedure copy_rest_of_file;
  (* copies the rest of the source file to the output file *)

procedure start_rule ( sym : Integer );
  (* start a new rule with lhs nonterminal symbol sym *)

procedure start_body;
  (* start a new rule body (rhs) *)

procedure end_body;
  (* end a rule body *)

procedure add_symbol ( sym : Integer );
  (* add the denoted symbol to the current rule body *)

procedure add_action;
  (* add an action to the current rule body *)

procedure add_rule_prec ( sym : Integer );
  (* add the precedence of terminal symbol sym to the current rule *)

procedure generate_parser;
  (* generate the parse table *)

implementation

uses YaccBase, YaccTabl, YaccClos, YaccLR0, YaccLook,
  YaccPars, YaccMsgs;

procedure yyerror ( msg : String );
  begin
    if msg='syntax error' then
      (* ignore *)
    else
      fatal(msg)
  end(*yyerror*);

function act_char : char;
  begin
    if cno>length(line) then
      if eof(yyin) then
        act_char := #0
      else
        act_char := nl
    else
      act_char := line[cno]
  end(*act_char*);

function lookahead_char : char;
  begin
    if succ(cno)>length(line) then
      if eof(yyin) then
        lookahead_char := #0
      else
        lookahead_char := nl
    else
      lookahead_char := line[succ(cno)]
  end(*lookahead_char*);

procedure next_char;
  begin
    if cno>length(line) then
      if eof(yyin) then
        { nop }
      else
        begin
          readln(yyin, line);
          inc(lno); cno := 1
        end
    else
      inc(cno)
  end(*next_char*);

var

(* Current rule: *)

act_rule      : RuleRec;

(* Actions: *)

n_act : Integer;
p_act : Boolean;

function sym ( k : Integer ) : Integer;
  var s : Integer;
  begin
    if is_def_key(k, s) then
      sym := s
    else if sym_table^[k].pname^[1]='''' then
      begin
        s := new_lit;
        def_key(k, s);
        sym := s;
      end
    else
      begin
        s := new_nt;
        def_key(k, s);
        sym := s;
      end
  end(*sym*);

function ntsym ( k : Integer ) : Integer;
  var s : Integer;
  begin
    if is_def_key(k, s) then
      if s<0 then
        ntsym := s
      else
        begin
          error(nonterm_expected);
          ntsym := -1;
        end
    else if sym_table^[k].pname^[1]='''' then
      begin
        error(nonterm_expected);
        ntsym := -1;
      end
    else
      begin
        s := new_nt;
        def_key(k, s);
        ntsym := s;
      end
  end(*ntsym*);

function litsym ( k : Integer; n : Integer ) : Integer;
  var s : Integer;
  begin
    if is_def_key(k, s) then
      if s>=0 then
        begin
          if n>0 then error(double_tokennum_def);
          litsym := s;
        end
      else
        begin
          error(literal_expected);
          litsym := 1;
        end
    else if sym_table^[k].pname^[1]='''' then
      begin
        if n>0 then
          begin
            add_lit(n);
            s := n;
          end
        else
          s := new_lit;
        def_key(k, s);
        litsym := s;
      end
    else
      begin
        if n>0 then
          begin
            add_lit(n);
            s := n;
          end
        else
          s := new_lit;
        def_key(k, s);
        writeln(yyout, 'const ', pname(s), ' = ', s, ';');
        litsym := s;
      end;
  end(*litsym*);

procedure next_section;
  var line : String;
  begin
    while not eof(yycod) do
      begin
        readln(yycod, line);
        if line='%%' then exit;
        writeln(yyout, line);
      end;
  end(*next_section*);

procedure definitions;
  var i : Integer;
  begin
    if n_types>0 then
      begin
        writeln(yyout);
        writeln(yyout, 'type YYSType = record case Integer of');
        for i := 1 to n_types do
          writeln(yyout, ' ':15, i:3, ' : ( ',
                         'yy', sym_table^[type_table^[i]].pname^, ' : ',
                         sym_table^[type_table^[i]].pname^, ' );');
        writeln(yyout, ' ':15, 'end(*YYSType*);');
      end;
  end(*definitions*);

procedure copy_code;
  var str_state : Boolean;
  begin
    str_state := false;
    while act_char<>#0 do
      if act_char=nl then
        begin
          writeln(yyout);
          next_char;
        end
      else if act_char='''' then
        begin
          write(yyout, '''');
          str_state := not str_state;
          next_char;
        end
      else if not str_state and (act_char='%') and (lookahead_char='}') then
        exit
      else