Re: goops and memoization

[Neil Jerram <neil@ossau.uklinux.net>]

>>>>> "Neil" == Neil Jerram <neil@ossau.uklinux.net> writes:

    Neil> If this is correct, the fix is to pass `x' through your memoizer just
    Neil> before `goto nontoplevel_begin;', like this:

    Neil> 	    apply_cmethod: /* inputs: z, arg1 */
    Neil> 	      {
    Neil> 		SCM formals = SCM_CMETHOD_FORMALS (z);
    Neil> 		env = EXTEND_ENV (formals, arg1, SCM_CMETHOD_ENV (z));
    Neil> 		x = SCM_CMETHOD_BODY (z);
    Neil>                 x = memoize (x);             /* ADDED */
    Neil> 		goto nontoplevel_begin;
    Neil> 	      }

And to follow up immediately to myself ... actually this is suboptimal
because it means that even a cached method is memoized every time it
is called.  (Also I was wrong about the lambda; the expression
returned by scm_memoize_method doesn't begin with a lambda.)

What we should really do is memoize before the method is installed
into the method cache.  I think the place for this is in
compute-entry-with-cmethod in oop/goops/compile.scm: just before
`(cons entry place-holder)':

(define (compute-entry-with-cmethod methods types)
  (or (code-table-lookup (slot-ref (car methods) 'code-table) types)
      (let* ((method (car methods))
	     (place-holder (list #f))
	     (entry (append types place-holder)))
	;; In order to handle recursion nicely, put the entry
	;; into the code-table before compiling the method 
	(slot-set! (car methods) 'code-table
		   (cons entry (slot-ref (car methods) 'code-table)))
	(let ((cmethod (compile-method methods types)))
	  (set-car! place-holder (car cmethod))
	  (set-cdr! place-holder (cdr cmethod)))
        (set-cdr! (cdr place-holder)                  ; ADDED
                  (memoize (cdr place-holder)))       ; ADDED
	(cons entry place-holder))))

   Neil



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