bison实例

逆波兰记号计算器【文件名rpcalc.y】

%{
#define YYSTYPE double
#include <stdio.h>
#include <math.h>
#include <ctype.h>
int yylex (void);
void yyerror (char const *);
%}

%token NUM

%%
input:    /* empty */
     | input line
    ;

line:     '\n'
    | exp '\n'      { printf ("\t%.10g\n", $); }
;

exp:      NUM           { $$ = $;           }
   | exp exp '+'   { $$ = $ + $;      }
    | exp exp '-'   { $$ = $ - $;      }
    | exp exp '*'   { $$ = $ * $;      }
    | exp exp '/'   { $$ = $ / $;      }
     /* Exponentiation */
    | exp exp '^'   { $$ = pow($, $); }
    /* Unary minus    */
    | exp 'n'       { $$ = -$;          }
;
%%

#include <ctype.h>

int yylex (void) {
       int c;

/* Skip white space.  */
       while ((c = getchar ()) == ' ' || c == '\t') ;

/* Process numbers.  */
       if (c == '.' || isdigit (c)) {
       ungetc (c, stdin);
       scanf ("%lf", &yylval);
       return NUM;
     }

       /* Return end-of-input.  */
       if (c == EOF) return ;

       /* Return a single char.  */
       return c;
}

void yyerror (char const *s) {
    fprintf (stderr, "%s\n", s);
}

int main (void) {
    return yyparse ();
}

------------------运行----------------------
bison rpcalc.y
gcc -o rpcalc -lm rpcalc.tab.c
./rpcalc
4 9 +
　　　　  13

中辍符号计算器【文件名calc.y】

%{
#define YYSTYPE double
#include <math.h>
#include <stdio.h>
int yylex (void);
void yyerror (char const *);
%}
/* Bison declarations.  */
%token NUM
%left '-' '+'
%left '*' '/'
%right '^'        /* exponentiation */
%% /* The grammar follows.  */
input:

| input line
;
line:
  '\n'
| exp '\n'  { printf ("\t%.10g\n", $); }
;
exp:
  NUM                { $$ = $;           }
| exp '+' exp        { $$ = $ + $;      }
| exp '-' exp        { $$ = $ - $;      }
| exp '*' exp        { $$ = $ * $;      }
| exp '/' exp        { $$ = $ / $;      }
| '-' exp               { $$ = -$;          }
| exp '^' exp        { $$ = pow ($, $); }
| '(' exp ')'        { $$ = $;           }
;
%%

#include <ctype.h>

int yylex (void) {
       int c;

/* Skip white space.  */
       while ((c = getchar ()) == ' ' || c == '\t') ;

/* Process numbers.  */
       if (c == '.' || isdigit (c)) {
       ungetc (c, stdin);
       scanf ("%lf", &yylval);
       return NUM;
     }

       /* Return end-of-input.  */
       if (c == EOF) return ;

       /* Return a single char.  */
       return c;
}

void yyerror (char const *s) {
    fprintf (stderr, "%s\n", s);
}

int main (void) {
    return yyparse ();
}

------------------运行----------------------
bison calc.y
gcc -o calc -lm calc.tab.c
./calc
8*(1+3)
　　　　  32