Plex and Pyacc
From Lazarus wiki
Free Pascal comes with substitutes for the GNU projects Lex and YACC. They are called Plex and Pyacc and they can be used to generate compilers and regular expression analyzers in Pascal instead of C.
Library contents
TP Lex and Yacc can be found here: http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/utils/tply/
Documentation
Download the manual here: http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/utils/tply/tply.doc?revision=1
Simple example application
This is a very simple calculator, which shows how to use plex and pyacc. The files in this simple project are:
- build.sh
- lexer.l
- parser.y
WARNING: The code below compiles but currently doesn't work
build.sh
plex lexer.l
pyacc -d parser.y
mv parser.pas calculadora.pas
fpc calculadora.pas
lexer.l
{ Analisador léxico da calculadora para a disciplina de PCS
Aluno: Felipe Monteiro de Carvalho }
%{
%}
%%
[0-9]+[dD]? begin yylval.yyInteger := StrToInt(yytext); yyruleno := NUMBER; end;
[0-9a-fA-F]+[hH] begin yylval.yyInteger := StrToInt(yytext); yyruleno := NUMBER; end;
[ \t] begin end; { ignorar espaços em branco }
[-] begin yyruleno := MENOS; end;
[+*/()] begin yyruleno := Integer(yytext[0]); end;
[=][hH] begin yyruleno := IGUALH; end;
[=][dD]? begin yyruleno := IGUALD; end;
\n begin yyruleno := Integer(yytext[0]); end;
. begin yyerror('Caracter inexperado'); end;
%%
function meuyywrap (): Integer;
begin
Result := 1;
end;
parser.y
/* Parser
Aluno: Felipe Monteiro de Carvalho */
%{
program calculadora;
{$mode delphi}
uses SysUtils, yacclib, lexlib;
%}
%start entrada
%token <Integer> NUMBER IGUALD IGUALH MENOS
%type <Integer> expressao termo fator
%%
entrada
: /* linha vazia */ { }
| entrada linha { }
;
linha
: expressao IGUALD '\n' { WriteLn(Format('Resultado: %d', [$1])); }
| expressao IGUALH '\n' { WriteLn(Format('Resultado: %H', [$1])); }
;
expressao
: expressao '+' termo { $$ := $1 + $3; }
| expressao MENOS termo { $$ := $1 - $3; }
| termo { $$ := $1; }
;
termo
: termo '*' fator { $$ := $1 * $3; }
| termo '/' fator { if ($3 = 0) then
yyerror('Divisao por zero!')
else
$$ := $1 div $3; }
| fator { $$ := $1; }
;
fator
: NUMBER { $$ := $1; }
| MENOS NUMBER { $$ := -1 * $2; }
| '(' expressao ')' { $$ := $2; }
;
%%
procedure meuyyerror(s: PChar); // Called by yyparse on error
begin
WriteLn(Format('Erro: %s', [s]));
end;
{$include lexer.pas}
begin
yywrap := @meuyywrap;
// yyerror := @meuyyerror;
yyparse ();
end.
How to use it
Type for example: 5+3=
And it will answer with: 8
You can also try 3*8=H to request an answer in Hexadecimal instead of decimal