%{
#include <stdio.h>
#include <ctype.h>

int yylex(void);
int yyerror(char *s);

#define YYSTYPE double  // data type of yacc stack
%}

%token NUMBER
%left '+' '-'   // left associative, same precedence
%left '*' '/'   // left associative, higher precedence

%%

exprlist: /* empty list */
    | exprlist '\n'
    | exprlist expr '\n' {printf("\t= %lf\n", $2);}
    ;

expr: NUMBER        {$$ = $1;}
    | expr '+' expr {$$ = $1 + $3;}
    | expr '-' expr {$$ = $1 - $3;}
    | expr '*' expr {$$ = $1 * $3;}
    | expr '/' expr {$$ = $1 / $3;}
    | '(' expr ')'  {$$ = $2;}
    ;

%%

char *progname;   // for error message
int lineno=1;

int main(int argc, char *argv[])
{
    progname=argv[0];
    yyparse();
    return 0;
}

// Print a warning messsage.
int warning(char *s, char *t)
{
    fprintf(stderr, "*** %s: %s", progname, s);
    
    if (t) fprintf(stderr, " %s", t);
    fprintf(stderr, " near line %d\n",lineno);
    return 0;
}

// Called for yacc syntax errors.
int yyerror(char *s)
{
    warning(s, (char *) 0);
    return 0;
}