expressionl2.pas

语法分析 语法分析

(* lexical analyzer template (TP Lex V3.0), V1.0 3-2-91 AG *)

(* global definitions: *)
 {*
    下面的例子改编自lex和yacc第二版
    识别简单算术表达式的lex
    用法：Lex Expression ExpressionL.dpr
 *}

unit ExpressionL2;

interface

uses
  SysUtils, LexLib, Yacclib;

const
  NUMBER = 258;

function yylex: Integer;

implementation
uses ExpressionY2;

function yylex: Integer;

  procedure yyaction(yyruleno: Integer);
    (* local definitions: *)
  begin
    (* actions: *)
    case yyruleno of
      1:
        begin
          yylval.yyreal := StrToFloat(yytext);
          return(NUMBER);
        end;
      2:
        ; {/* 忽略空格 *}
      3:
        return(0); {* 当回车时，重置状态 *}
      4:
        returnc(yytext[1]);
      {returnc用来返回字符串，另外要返回的第一个字符是yytext[1]而不是yytext[0]}
    end;
  end (*yyaction*);

  (* DFA table: *)

type
  YYTRec = record
    cc: set of Char;
    s: Integer;
  end;

const

  yynmarks = 7;
  yynmatches = 7;
  yyntrans = 10;
  yynstates = 7;

  yyk: array[1..yynmarks] of Integer = (
    { 0: }
    { 1: }
    { 2: }
    1,
    4,
    { 3: }
    2,
    4,
    { 4: }
    3,
    { 5: }
    4,
    { 6: }
    1
    );

  yym: array[1..yynmatches] of Integer = (
    { 0: }
    { 1: }
    { 2: }
    1,
    4,
    { 3: }
    2,
    4,
    { 4: }
    3,
    { 5: }
    4,
    { 6: }
    1
    );

  yyt: array[1..yyntrans] of YYTrec = (
    { 0: }
    (cc: [#1..#8, #11..#31, '!'..'/', ':'..#255]; s: 5),
    (cc: [#9, ' ']; s: 3),
    (cc: [#10]; s: 4),
    (cc: ['0'..'9']; s: 2),
    { 1: }
    (cc: [#1..#8, #11..#31, '!'..'/', ':'..#255]; s: 5),
    (cc: [#9, ' ']; s: 3),
    (cc: [#10]; s: 4),
    (cc: ['0'..'9']; s: 2),
    { 2: }
    (cc: ['0'..'9']; s: 6),
    { 3: }
    { 4: }
    { 5: }
    { 6: }
    (cc: ['0'..'9']; s: 6)
    );

  yykl: array[0..yynstates - 1] of Integer = (
    { 0: } 1,
    { 1: } 1,
    { 2: } 1,
    { 3: } 3,
    { 4: } 5,
    { 5: } 6,
    { 6: } 7
    );

  yykh: array[0..yynstates - 1] of Integer = (
    { 0: } 0,
    { 1: } 0,
    { 2: } 2,
    { 3: } 4,
    { 4: } 5,
    { 5: } 6,
    { 6: } 7
    );

  yyml: array[0..yynstates - 1] of Integer = (
    { 0: } 1,
    { 1: } 1,
    { 2: } 1,
    { 3: } 3,
    { 4: } 5,
    { 5: } 6,
    { 6: } 7
    );

  yymh: array[0..yynstates - 1] of Integer = (
    { 0: } 0,
    { 1: } 0,
    { 2: } 2,
    { 3: } 4,
    { 4: } 5,
    { 5: } 6,
    { 6: } 7
    );

  yytl: array[0..yynstates - 1] of Integer = (
    { 0: } 1,
    { 1: } 5,
    { 2: } 9,
    { 3: } 10,
    { 4: } 10,
    { 5: } 10,
    { 6: } 10
    );

  yyth: array[0..yynstates - 1] of Integer = (
    { 0: } 4,
    { 1: } 8,
    { 2: } 9,
    { 3: } 9,
    { 4: } 9,
    { 5: } 9,
    { 6: } 10
    );

var
  yyn: Integer;

label
  start, scan, action;

begin

  start:

  (* initialize: *)

  yynew;

  scan:

  (* mark positions and matches: *)

  for yyn := yykl[yystate] to yykh[yystate] do
    yymark(yyk[yyn]);
  for yyn := yymh[yystate] downto yyml[yystate] do
    yymatch(yym[yyn]);

  if yytl[yystate] > yyth[yystate] then
    goto action; (* dead state *)

  (* get next character: *)

  yyscan;

  (* determine action: *)

  yyn := yytl[yystate];
  while (yyn <= yyth[yystate]) and not (yyactchar in yyt[yyn].cc) do
    inc(yyn);
  if yyn > yyth[yystate] then
    goto action;
  (* no transition on yyactchar in this state *)

(* switch to new state: *)

  yystate := yyt[yyn].s;

  goto scan;

  action:

  (* execute action: *)

  if yyfind(yyrule) then
  begin
    yyaction(yyrule);
    if yyreject then
      goto action;
  end
  else if not yydefault and yywrap then
  begin
    yyclear;
    return(0);
  end;

  if not yydone then
    goto start;

  yylex := yyretval;

end (*yylex*);

end.