> On Jun 3, 2019, at 9:09 AM, Matthias Felleisen <matth...@felleisen.org> wrote:
>
>
> Or,
>
> #lang racket
>
> (require (for-syntax ) racket/stxparam)
>
> (define-syntax-parameter return (syntax-rules ()))
> (define-syntax-parameter false (syntax-rules ()))
>
> (define-syntax fn
> (syntax-rules ()
> [(_ (arg ...) body ...)
> (λ (arg ...)
> (let/cc fn-exit
> (syntax-parameterize ([return (syntax-rules () [(_ x) (fn-exit x)])])
> (syntax-parameterize ([false (syntax-rules () [(_) (return #f)])])
> body ...))))]))
>
> ((fn (x y) (when (< x y) (return x)) y) 2 30) ; => 2
> ((fn (x y) (when (< x y) (false)) y) 2 30) ;=> #f
>
Oh! I see! That solves the expansio issue! Wonderful. You’ve opened up a whole
new set of possibilities for me. Thanks, Matthias.
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