expr.y revision 1.1.1.1 
1/*	$NetBSD: expr.y,v 1.1.1.1 2009/10/26 00:28:33 christos Exp $	*/
2
3/*
4 * expr.y : A simple yacc expression parser
5 *          Based on the Bison manual example.
6 */
7
8%{
9#include <stdio.h>
10#include <math.h>
11
12%}
13
14%union {
15   float val;
16}
17
18%token NUMBER
19%token PLUS MINUS MULT DIV EXPON
20%token EOL
21%token LB RB
22
23%left  MINUS PLUS
24%left  MULT DIV
25%right EXPON
26
27%type  <val> exp NUMBER
28
29%%
30input   :
31        | input line
32        ;
33
34line    : EOL
35        | exp EOL { printf("%g\n",$1);}
36
37exp     : NUMBER                 { $$ = $1;        }
38        | exp PLUS  exp          { $$ = $1 + $3;   }
39        | exp MINUS exp          { $$ = $1 - $3;   }
40        | exp MULT  exp          { $$ = $1 * $3;   }
41        | exp DIV   exp          { $$ = $1 / $3;   }
42        | MINUS  exp %prec MINUS { $$ = -$2;       }
43        | exp EXPON exp          { $$ = pow($1,$3);}
44        | LB exp RB                      { $$ = $2;        }
45        ;
46
47%%
48
49yyerror(char *message)
50{
51  printf("%s\n",message);
52}
53
54int main(int argc, char *argv[])
55{
56  yyparse();
57  return(0);
58}
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