toolset: simplifier

The idea of the simplifier is to replace 'complex' expressions by 'simpler' ones. We do this using rewrite rules that replace expressions 'a+b' and 'a*b' by their resp. value. As our language only contains operators '+' and '*', and constants, as the result of simplifying an expression we get a constant with the value of the expression.

Intended usage on the shell command line:


$ echo '(1+1)*(1+1)' | parser | simplifier | unparser

Example:

input:: (1+1)*(1+1)
output:: 4

Rewrite rules:

Plus(  Const( i ), Const( j ))   ->  Const(  cplus( i, j ));
Times( Const( i ), Const( j ))   ->  Const( ctimes( i, j ));

Main routine:


#include "k.h"                 /* data type defs */
#include "csgiok.h"    /* structure file io defs */
#include "rk.h"                  /* rewrite defs */

int main() {
  char *io;            /* error message, or == 0 */
  expr the_expr;       /* root of the parse tree */
  io = CSGIOread_expr(stdin, &the_expr);
  if (io != 0)                         /* error! */
      fatal("Read error: %s\n", io);
      the_expr = rewrite_expr(the_expr, base_rview);
  io = CSGIOwrite_expr(stdout, the_expr);
  if (io != 0)                         /* error! */
      fatal("Write error: %s\n", io);
  exit(0);                           /* success! */
}

Utility routines, defned as file compute.k:


%{ KC_REWRITE  /* export fn defs to rewrite code */
#include "compute.h"
%}

int cplus( int i, int j) {
  return i + j;
}

int ctimes( int i, int j) {
  return i * j;
}

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Last updated at 23 February '01 by kimwitu@cs.utwente.nl