Here's a modification to the code I posted below. It lets the variable
transformers work with anything, not just nth.
@@ -8,7 +8,7 @@
((_ #(expr "string") n)
(string-ref expr n))
((_ spec n)
- (spec n))))
+ (spec nth n))))
(define-syntax define-typed
(lambda (stx)
@@ -21,8 +21,8 @@
(let-syntax ((arg (make-variable-transformer
(lambda (stx)
(syntax-case stx (set!)
- ((_ n)
- (syntax (nth #(t type) n)))
+ ((_ m a (... ...))
+ (syntax (m #(t type) a (... ...))))
(_ (identifier? stx)
(syntax t))
((set! _ val)
--
: Derick
----------------------------------------------------------------
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
> (syntax-rules ()
> ((_ #(expr "list") n)
> (list-ref expr n))
> ((_ #(expr "vector") n)
> (vector-ref expr n))
> ((_ #(expr "string") n)
> (string-ref expr n))
> ((_ spec n)
> (spec n))))
>
> (define-syntax define-typed
> (lambda (stx)
> (syntax-case stx ()
> ((_ (name #(arg type) ...) . body)
> (with-syntax
> (((t ...) (generate-temporaries (syntax (arg ...)))))
> (syntax
> (define (name t ...)
> (let-syntax ((arg (make-variable-transformer
> (lambda (stx)
> (syntax-case stx (set!)
> ((_ n)
> (syntax (nth #(t type) n)))
> (_ (identifier? stx)
> (syntax t))
> ((set! _ val)
> (syntax (set! t val)))))))
> ...)
> . body))))))))
>
>
> (define-typed (foo #(s "string") #(l "list"))
> (values (nth s 2) (nth l 3)))
>
> (foo "abc" (quote (a b c d)))
> =>
> #\c
> d
>
>
