%{
#include <stdio.h>
#include <stdlib.h>
void yyerror(char *s);
%}

%token MONTH
%token DAY
%token COMMA
%token YEAR

%%

date : MONTH TWODIGITTHINGY COMMA FOURDIGITTHINGY
     | TWODIGITTHINGY MONTH FOURDIGITTHINGY
     | TWODIGITTHINGY SLASH TWODIGITTHINGY SLASH year ;

year : TWODIGITTHINGY | FOURDIGITTHINGY ;


%%
extern FILE *yyin;

int main(int argc, char *argv[])
{
   if (argc < 2) { fprintf(stderr, "usage: dates filename\n"); exit(-1); }
   yyin = fopen(argv[1],"r");
   if (yyparse() == 0) printf("no errors\n");
   else printf("there were errors\n");
}

void yyerror(char *s)
{
   printf("%s\n", s);
}