20 minutes ago, J. Ian Johnson wrote:
> I have a syntax parameter that is bound to a transformer. I want to
> (at certain points) change the parameterization of this parameter to
> a new transformer that depends on the old one.
>
> I can't do this:
> #'(syntax-parameterize ([p (syntax-parser
> [pat (some-combination-of (syntax-parameter-value
> #'p) pat))])])
> blah)
>
> Because the value fetched is the inner most one, but I want what it
> is currently.
So you need to grab it outside of the new tansformer, just like with
plain parameters and closures.
#lang racket/base
;; for fun
(require (for-syntax racket/base) racket/stxparam)
(define-syntax-parameter foo #'0)
(define-syntax (the-foo stx)
#`'#,(syntax-parameter-value #'foo))
(define-syntax (foo-add stx)
(syntax-case stx ()
[(_ stuff body ...)
#`(syntax-parameterize ([foo #'(stuff #,(syntax-parameter-value #'foo))])
body ...)]))
the-foo
(foo-add 1 (foo-add 2 the-foo))
;; IIUC, this is what you want
(define-syntax-parameter bar (λ (stx) #'0))
(define-syntax (bar-add stx)
(syntax-case stx ()
[(_ stuff body ...)
(let* ([cur (syntax-parameter-value #'bar)]
[new (λ (stx) #`(stuff #,(cur stx)))])
#`(syntax-parameterize ([bar #,new])
body ...))]))
bar
(bar-add add1 (bar-add list bar))
--
((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
http://barzilay.org/ Maze is Life!
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