Re: regex-case

[Matt Wette]

Matt Wette
matthew.we...@verizon.net



> On Feb 8, 2016, at 7:40 AM, Stefan Israelsson Tampe <stefan.ita...@gmail.com> 
> wrote:
> ---------- Forwarded message ----------
> From: Stefan Israelsson Tampe <stefan.ita...@gmail.com 
> <mailto:stefan.ita...@gmail.com>>
> Date: Mon, Feb 8, 2016 at 4:31 PM
> Subject: Re: regex-case
> To: Ludovic Courtès <l...@gnu.org <mailto:l...@gnu.org>>
> 
> 
> An interesting question is what can be done by ice-9/match

To provide background to the guile-devel list my prototype implementation for 
regex-case is as follows (w/ error messages suggested by Ludo now included):

;; helper macro for regex-case
;; (rx-let m (v ...) exp ...) => (let ((v (match:substring m 1)) ...) exp ...)
(define-syntax rx-let
  (lambda (x)
    (syntax-case x ()
      ((_ m (v ...) exp ...)
       (with-syntax (((i ...)
                      (let f ((n 1) (vl #'(v ...))) ; fold (v ...) to (1 ...)
                        (if (null? vl) '() (cons n (f (1+ n) (cdr vl)))))))
         #'(let ((v (match:substring m i)) ...) exp ...))))))

(define-syntax regex-case
  (lambda (x)
    (syntax-case x (else)
      ((_ str ((pat v ...) exp ...) ...)
       (with-syntax (((id ...) (generate-temporaries #'(pat ...))))
         #'(let ((id (make-regexp pat)) ...)
             (cond
              ((regexp-exec id str) =>
               (lambda (m) (rx-let m (v ...) exp ...)))
              ...
              (else (error "regex-case: no match"))))))
      ((_ str ((pat v ...) exp ...) ... (else else-exp ...))
       (with-syntax (((id ...) (generate-temporaries #'(pat ...))))
         #'(let ((id (make-regexp pat)) ...)
             (cond
              ((regexp-exec id str) =>
               (lambda (m) (rx-let m (v ...) exp ...)))
              ...
             (else else-exp ...))))))))