/* 
 * Yacc/bison input file for a simple expression evaluator. 
 * Adapted from Louden, p. 229.
 * Further adapted to use a lex-generated scanner.
 */

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

#define YYSTYPE float
%}

%token NUMBER PLUS MINUS TIMES DIVIDES LPAREN RPAREN NEWLINE ERROR

%%

commands 
    : commands command
    | command
    ;

command 
    : exp NEWLINE  { printf("%g\n", $1); } 
    | NEWLINE  { }
    ;

exp : exp PLUS term  { $$ = $1 + $3; }
    | exp MINUS term  { $$ = $1 - $3; }
    | term  { $$ = $1; }
    ;

term
    : term TIMES factor  { $$ = $1 * $3; }
    | term DIVIDES factor  { $$ = $1 / $3; }
    | factor  { $$ = $1; }
    ;

factor 
    : NUMBER  { $$ = $1; }
    | LPAREN exp RPAREN  { $$ = $2; }
    ;

%%

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

/* report errors */
int yyerror(char *s) {
    fprintf(stderr, "%s\n", s);
}