Re: [Kawa-commonlisp-dev] tagbodies

[Jamison Hope]

On Jul 27, 2012, at 11:23 AM, Charles Turner wrote:

> On 27 July 2012 13:46, Charles Turner <address@hidden> wrote:
> > On 27 July 2012 13:02, Charles Turner <address@hidden> wrote:
> > > On 26 July 2012 21:12, Jamison Hope <address@hidden> wrote:
> > > > LABELS is very similar to Scheme's letrec, so I would expect the
> > > > amount of work to get a working LABELS to be about what you had  
> > > > to do to
> > > > make FLET based on LET (i.e. not too much).
> > >
> > > Maybe I should just copy the thing in my primitives file and  
> > > somehow modify it
> > > to to call this method?
> >
> > Or better just call FLET instead of %let...
>
> I'm struggling to get this working.
>
> I won't quote LETREC, as it's quite large, it can be found in
> kawa/lib/prim_syntax.scm
>
> My first idea was to replace (process-binding ..) with (funcall
> process-binding ...) in the macro. However, line 122 (of prim_syntax
> when replaced like this) throws a (paraphrased)
> APPLY - wrong type (kawa.lang.SyntaxForms$SimpleSyntaxForm cannot be
> cast to gnu.mapping.procedure) because of the (syntax bindings) bit.
> (My FUNCALL is implementing in terms of APPLY).
>
> The next attempt was to use FLET instead. (flet ((process-binding ()
> #undefined)) (set! process-binding (lambda (b) ...)) ...). That didn't
> work, process-binding just returns #!undefined... Seemed a bit wacky
> anyway. I naively thought I could call settingProcedureDecls on
> process-binding, but it's compiled into a ModuleMethod so I can't do
> that. Am I missing something obvious?

OK, I hadn't noticed how... cleverly, let's say, letrec was implemented
in prim_syntax. Let's just use that as some loose inspiration instead.
Notice that it expands

(letrec ((a a-init)
         (b b-init))
  e ...)

into

(let ((a #!undefined)
      (b #!undefined))
  (set! a a-init)
  (set! b b-init)
  e ...)

So since we now have a working FLET, how about something like this:

(define-syntax labels
  (syntax-rules ()
    ((labels ((fname parameters body ...) ...) e ...)
     (flet ((fname parameters #!void) ...)
       (set! #'fname (lambda parameters body ...)) ...
       e ...))))

Seems to work:

(labels ((e (n) (or (= 0 n) (o (- n 1))))
         (o (n) (not (e n))))
  (e 512))
=> t




-Jamie

--
Jamison Hope
The PTR Group
www.theptrgroup.com