%{
/* C DECLARATIONS */
#include <stdio.h>
#include <stdlib.h>
void yyerror( char *s);
int yylex();
#define YYDEBUG 1
#define YYERROR_VERBOSE 1
#define YYINITDEPTH 20
%}

/* BISON DECLARATIONS */
%raw
%token NUM

%%
/* GRAMMAR RULES */
A: 	NUM		{ printf("%d\n",$$); }
	| A '+' NUM { $$ = $1 + $3; printf("%d\n",$$); }
	| A '-' NUM { $$ = $1 - $3; printf("%d\n",$$); };

%%
/* ADDITIONAL C CODE */
FILE* input_file;

int yylex()
{	int c;
yylex1:
    switch( c=getc(input_file))
    {	case EOF: printf("end of file\n");
		    return 0;
	case '+': printf("+ returned\n");
		    return '+';
	case '-': printf("- returned\n");
		    return '-';
	case '#':   {	fscanf(input_file,"%d",&yylval);
			printf("%d returned\n",yylval);
			return NUM;
		    }
	default: break;
    }
    goto yylex1;
}

int main()
{
#if YYDEBUG != 0
    yydebug = -1;
#endif
    if( (input_file=fopen("input.txt","r")) == NULL)
	{printf("opening file error\n"); return -1;}
    if( yyparse() != 0 ) printf("unknown error\n");
    if( fclose( input_file) == EOF)
	{printf("closing file error\n"); return -1;}
    return 0;
}

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