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problems with syntax-case and with-syntax


From: Matt Wette
Subject: problems with syntax-case and with-syntax
Date: Sun, 27 Aug 2017 13:18:20 -0700

Q1) The code below creates two macros.  One called `define-foo' which generates 
a new identifier and 
then defines that to #t.  The other, `define-foo/p', generates the same 
identifier (lexical issue?) 
and another identifier, then "calls" define-foo and then uses both identifiers 
in a `define'.  When
executed I get this error:

scheme@(guile-user)> (define-foo/p abc)
;;; <stdin>:2:0: warning: possibly unbound variable `wrap-abc'
<unnamed port>:2:0: <unnamed port>:2:0: In procedure module-lookup: Unbound 
variable: wrap-abc

What am I doing wrong here?


Q2) Also with respect to the code below.  Is there any way to pull the 
definitions for stx->str
and gen-id out of the define-syntax body to make them general purpose?


This code being developed under guile-2.2.2.

The code:

(define-syntax define-foo
  (lambda (x)
    (define (stx->str stx)
      (symbol->string (syntax->datum stx)))
    (define (gen-id tmpl-id . args)
      (datum->syntax
       tmpl-id
       (string->symbol
        (apply string-append
               (map (lambda (ss) (if (string? ss) ss (stx->str ss))) args)))))
    (syntax-case x ()
      ((_ name)
       (with-syntax ((wrap (gen-id x "wrap-" #'name)))
         #'(begin
             (define wrap #t)))))))

(define-syntax define-foo/p
  (lambda (x)
    (define (stx->str stx)
      (symbol->string (syntax->datum stx)))
    (define (gen-id tmpl-id . args)
      (datum->syntax
       tmpl-id
       (string->symbol
        (apply string-append
               (map (lambda (ss) (if (string? ss) ss (stx->str ss))) args)))))
    (syntax-case x ()
      ((_ name)
       (with-syntax ((wrap (gen-id x "wrap-" #'name))
                     (rewrap (gen-id x "rewrap-" #'name)))
         #'(begin
             (define-foo name)
             (define rewrap wrap)))))))

;;(define-foo/p abc)
;; expect:
;; (define wrap-abc #t)
;; (define rewrap-abc wrap-abc)

;;(define-foo abc) ;; works (but does not define rewrap-abc
;; expect:
;; (define wrap-abc #t)


Thanks for the help,
Matt




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