GNU bison

GNU Bison is a free parser generator computer program written for the GNU project, and available for virtually all common operating systems. It is mostly compatible with Yacc, and offers several improvements over the earlier program. It is commonly used in conjunction with flex.

Bison converts a grammar description for a LALR context-free grammar into a C or C++ program to parse that grammar.

http://www.gnu.org/software/bison/

Examples

touch parse.y

%{
#include<stdio.h>
%}

%token NUM
%left '+' '-'
%left '*' '/'

%start line 

%%

line:   
       /* empty */ 
     |line exp '\n' {printf("%d\n",$2);}
     | error '\n';

exp:      exp '+' exp {$$ = $1 + $3;}
        | exp '*' exp {$$ = $1 * $3;}
        | exp '-' exp {$$ = $1 - $3;}
        | exp '/' exp { if ($3 == 0)
                                $$ = 0;
                        else
                                $$ = $1/$3;}
        | NUM          {$$ = $1;};
%%

yyerror()
{
        printf("Error detected in parsing\n");
}

main()
{
        yyparse();
}

bison parse.y