; Author: Juergen Lorenz ; ju (at) jugilo (dot) de
;
; Copyright (c) 2016, Juergen Lorenz
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#|[
Besides the documentation procedure, this module exports only one macro,
->proc, and a sharp-read-macro, ##, which abbreviates the call of 
that macro.

The macro transforms expressions with zero or more holes into a
procedure. Insofar, it's a bit like cut or cute. But while in cut or
cute a hole is the special identifier <>, in this module it's a pair of
bangs, possibly enclosing a sequence of digits, for examples !! or !1!.
In this way, holes needn't name different variables like in cut or cute.

Another difference to cut or cute is, that the holes may appear in
nested expressions at different levels. This gives great flexibility.
And the sharp-read-syntax ## adds ease of use.
]|#

(require-library irregex)

(module holes (->proc holes)
  (import scheme
          (only chicken print set-sharp-read-syntax!))

(import-for-syntax
  (only chicken foldr)
  (only irregex sre->irregex irregex-extract)
  (only data-structures ->string))

(define-syntax ->proc
  (er-macro-transformer
    (lambda (form rename compare?)
      (let ((code (cdr form))
            (%lambda (rename 'lambda)))
        (let ((irx (sre->irregex
                     '(: (or space "(")
                         "!"
                         (* (/ "09"))
                         "!"
                         (or space ")"))))
;              (foldr (lambda (op acc lst)
;                       (let loop ((lst lst))
;                         (if (null? lst)
;                           acc
;                           (op (car lst)
;                               (loop (cdr lst)))))))
              (adjoin (lambda (sym syms)
                        (if (memq sym syms)
                          syms
                          (cons sym syms))))
              )
          `(,%lambda
             ,(foldr adjoin '() ; remove dups
                     (map string->symbol
                          (map (lambda (str)
                                 (substring str 1 (- (string-length str) 1)))
                               (irregex-extract irx (->string code)))))
             ,@code))))))

(set-sharp-read-syntax! #\#
  (lambda (port) `(->proc ,(read port))))

(define (holes)
  (for-each print
    (list "->proc"
          "macro:"
          "(->proc xpr)"
          "  extracts holes, i.e. a pair of bangs"
          "  possible enclosing a seqence of digits"
          "  form xpr, removes duplicates, and uses"
          "  the resulting list as arbument list of"
          "  a procedure with body xpr"
          "  can be called with sharp-read-syntax ##")))

) ; module holes