Thanks a lot. Am 03.10.2017 9:05 nachm. schrieb "Matthew Butterick" <[email protected]>:
> > > On Oct 3, 2017, at 10:31 AM, 'Shakin Billy' via Racket Users < > [email protected]> wrote: > > > > how do i access the pattern variable var at compile time (phase 1?) > > additional to an answer, could you point me to the right part of the > documentation? i really couldn't find it. > > > `var` isn't a `procedure?` during phase 1. It's just a piece of syntax. So > your `cond`, which is evaluated in phase 1, will always fail. > > But if you shift the `cond` to phase 0, by putting it inside the syntax > template, it will work: > > > #lang racket > (require rackunit) > (define inp (open-input-string "12+34")) > > (define-syntax (terminal stx) > (syntax-case stx () > ((_ name rx) > (if (pregexp? (syntax->datum #'rx)) > #'(define (name) > (regexp-try-match rx inp)) > #'(error "Pregexp expected."))))) > > (define-syntax (prod stx) > (syntax-case stx () > ((_ prod-name (name var)) > #'(cond > ((procedure? var) 0) > (else (error 'PROD-ARGUMENTS "Pregexp oder Procedure > expected.")))))) > > (terminal digit #px"\\d") > (check-equal? (prod term (op1 digit)) 0) > > (define not-a-procedure 42) > (check-exn exn:fail? (λ () (prod term (op1 not-a-procedure)))) -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
