On Tue, 2009-09-29 at 15:51 -0700, Derick Eddington wrote:
> On Sun, 2009-09-27 at 16:59 -0500, Eduardo Cavazos wrote:
> > Now, it would be nice to be able to say:
> >
> > (define-typed (abc #(seq "string"))
> > (nth seq 2))
>
> > But that has at least one problem.
>
> > So, any suggestions for how to approach 'define-typed'?
>
> Here's a way. It requires coordination with the macros like nth.
>
> (define-syntax nth
> [...]
> (define-syntax define-typed
> [...]
If I were really going to use this, I'd abstract-away the making of the
variable transformers:
(define (make-arg-type-T id type) ;; Needs to be in separate library.
(make-variable-transformer
(lambda (stx)
(syntax-case stx (set!)
((_ m a ...)
(quasisyntax (m #((unsyntax id) (unsyntax type)) a ...)))
(_ (identifier? stx)
id)
((set! _ val)
(quasisyntax (set! (unsyntax id) val)))))))
(define-syntax define-typed
(lambda (stx)
(syntax-case stx ()
((_ (name #(arg type) ...) . body)
(with-syntax*
(((t ...) (generate-temporaries (syntax (arg ...))))
((make ...)
(map (lambda (x) (cons (syntax make-arg-type-T) x))
(syntax (((syntax t) (syntax type)) ...)))))
(syntax
(define (name t ...)
(let-syntax ((arg make) ...) . body))))))))
[1] with-syntax* is:
(define-syntax with-syntax*
(syntax-rules ()
((_ (pc0 pc1 pc* ...) . b)
(with-syntax (pc0)
(with-syntax* (pc1 pc* ...) . b)))
((_ pc . b)
(with-syntax pc . b))))
--
: Derick
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