subst.cpp

   1 /*      Substitute new expr for old expr in expr.
   2
   3         Input:  push    expr
   4
   5                 push    old expr
   6
   7                 push    new expr
   8
   9         Output: Result on stack
  10 */
  11
  12 #include "stdafx.h"
  13 #include "defs.h"
  14
  15 void
  16 subst(void)
  17 {
  18         int i;
  19         save();
  20         p3 = pop(); // new expr
  21         p2 = pop(); // old expr
  22         if (p2 == symbol(NIL) || p3 == symbol(NIL)) {
  23                 restore();
  24                 return;
  25         }
  26         p1 = pop(); // expr
  27         if (istensor(p1)) {
  28                 p4 = alloc_tensor(p1->u.tensor->nelem);
  29                 p4->u.tensor->ndim = p1->u.tensor->ndim;
  30                 for (i = 0; i < p1->u.tensor->ndim; i++)
  31                         p4->u.tensor->dim[i] = p1->u.tensor->dim[i];
  32                 for (i = 0; i < p1->u.tensor->nelem; i++) {
  33                         push(p1->u.tensor->elem[i]);
  34                         push(p2);
  35                         push(p3);
  36                         subst();
  37                         p4->u.tensor->elem[i] = pop();
  38                 }
  39                 push(p4);
  40         } else if (equal(p1, p2))
  41                 push(p3);
  42         else if (iscons(p1)) {
  43                 push(car(p1));
  44                 push(p2);
  45                 push(p3);
  46                 subst();
  47                 push(cdr(p1));
  48                 push(p2);
  49                 push(p3);
  50                 subst();
  51                 cons();
  52         } else
  53                 push(p1);
  54         restore();
  55 }