Re: regex-case

[Matt Wette]

Matt Wette

address@hidden

On Feb 8, 2016, at 7:40 AM, Stefan Israelsson Tampe <address@hidden> wrote:

---------- Forwarded message ----------
From: Stefan Israelsson Tampe <address@hidden>
Date: Mon, Feb 8, 2016 at 4:31 PM
Subject: Re: regex-case
To: Ludovic Courtès <address@hidden>

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 ...))))))))