external/bsd/flex/dist/examples/manual/expr.y

   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 %%
  30 input   :
  31         | input line
  32         ;
  33
  34 line    : EOL
  35         | exp EOL { printf("%g\n",$1);}
  36
  37 exp     : 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
  49 yyerror(char *message)
  50 {
  51   printf("%s\n",message);
  52 }
  53
  54 int main(int argc, char *argv[])
  55 {
  56   yyparse();
  57   return(0);
  58 }
  59
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