Bison: orig.y

%{
#include <stdio.h>
#include "orig.tab.h"
#include "lex.yy.c"
int yylex(void);
void yyerror(const char *);
extern FILE *yyin;

int memori = 0, memori_rsl = 0;
%}

%token KAZU
%token MPLUS MMINUS MPRINT MCLEAR
%left '-' '+'
%left '/' '*'
%precedence VTOKEN

%%

source:
  /* empty */
| source bun
;

bun:
  shiki ';' { printf("%d\n", $1); memori = $1; }
| memori ';'
;

shiki:
  KAZU
| tasu
| hiku
| waru
| kakeru
| '-' shiki %prec VTOKEN { $$ = -$2; }
| '(' shiki ')' { $$ = $2; }
;

tasu:
  shiki '+' shiki { $$ = $1 + $3; }
;

hiku:
  shiki '-' shiki { $$ = $1 - $3; }
;

waru:
  shiki '/' shiki {
    if ($3) $$ = $1 / $3;
    else {
      $$ = 1;
      fprintf(stderr, "division by zero: \"%d / %d\"\n", $1, $3);
    }
  }
;

kakeru:
  shiki '*' shiki { $$ = $1 * $3; }
;

memori:
  MPLUS { memori_rsl += memori; }
| MMINUS { memori_rsl -= memori; }
| MPRINT { printf("memori_rsl = %d\n", memori_rsl); }
| MCLEAR { memori = memori_rsl = 0; }
;

%%

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

int main(int argc, char *argv[]) {
  if (argc != 2) return 1;
  yyin = fopen(argv[1], "r");
  return yyparse();
}