define.cpp

   1 // Store a function definition
   2 //
   3 // Example:
   4 //
   5 //      f(x,y)=x^y
   6 //
   7 // For this definition, p1 points to the following structure.
   8 //
   9 //     p1
  10 //      |
  11 //   ___v__    ______                        ______
  12 //  |CONS  |->|CONS  |--------------------->|CONS  |
  13 //  |______|  |______|                      |______|
  14 //      |         |                             |
  15 //   ___v__    ___v__    ______    ______    ___v__    ______    ______
  16 //  |SETQ  |  |CONS  |->|CONS  |->|CONS  |  |CONS  |->|CONS  |->|CONS  |
  17 //  |______|  |______|  |______|  |______|  |______|  |______|  |______|
  18 //                |         |         |         |         |         |
  19 //             ___v__    ___v__    ___v__    ___v__    ___v__    ___v__
  20 //            |SYM f |  |SYM x |  |SYM y |  |POWER |  |SYM x |  |SYM y |
  21 //            |______|  |______|  |______|  |______|  |______|  |______|
  22 //
  23 // We have
  24 //
  25 //      caadr(p1) points to f
  26 //      cdadr(p1) points to the list (x y)
  27 //      caddr(p1) points to (power x y)
  28
  29 #include "stdafx.h"
  30 #include "defs.h"
  31
  32 #define F p3 // F points to the function name
  33 #define A p4 // A points to the argument list
  34 #define B p5 // B points to the function body
  35
  36 void
  37 define_user_function(void)
  38 {
  39         F = caadr(p1);
  40         A = cdadr(p1);
  41         B = caddr(p1);
  42
  43         if (!issymbol(F))
  44                 stop("function name?");
  45
  46         // evaluate function body (maybe)
  47
  48         if (car(B) == symbol(EVAL)) {
  49                 push(cadr(B));
  50                 eval();
  51                 B = pop();
  52         }
  53
  54         set_binding_and_arglist(F, B, A);
  55
  56         // return value is nil
  57
  58         push_symbol(NIL);
  59 }