53 lines
2.1 KiB
Scheme
53 lines
2.1 KiB
Scheme
|
;;; setof.ss
|
||
|
;;; Copyright (C) 1996 R. Kent Dybvig
|
||
|
;;; from "The Scheme Programming Language, 2ed" by R. Kent Dybvig
|
||
|
|
||
|
;;; Permission is hereby granted, free of charge, to any person obtaining a
|
||
|
;;; copy of this software and associated documentation files (the "Software"),
|
||
|
;;; to deal in the Software without restriction, including without limitation
|
||
|
;;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
|
||
|
;;; and/or sell copies of the Software, and to permit persons to whom the
|
||
|
;;; Software is furnished to do so, subject to the following conditions:
|
||
|
;;;
|
||
|
;;; The above copyright notice and this permission notice shall be included in
|
||
|
;;; all copies or substantial portions of the Software.
|
||
|
;;;
|
||
|
;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
||
|
;;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
||
|
;;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
|
||
|
;;; THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
||
|
;;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
|
||
|
;;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
|
||
|
;;; DEALINGS IN THE SOFTWARE.
|
||
|
|
||
|
;;; set-of uses helper syntactic extension set-of-help, passing it
|
||
|
;;; an initial base expression of '()
|
||
|
(define-syntax set-of
|
||
|
(syntax-rules ()
|
||
|
((_ e m ...)
|
||
|
(set-of-help e '() m ...))))
|
||
|
|
||
|
;;; set-of-help recognizes in, is, and predicate expressions and
|
||
|
;;; changes them into nested named let, let, and if expressions.
|
||
|
(define-syntax set-of-help
|
||
|
(syntax-rules (in is)
|
||
|
((_ e base)
|
||
|
(set-cons e base))
|
||
|
((_ e base (x in s) m ...)
|
||
|
(let loop ((set s))
|
||
|
(if (null? set)
|
||
|
base
|
||
|
(let ((x (car set)))
|
||
|
(set-of-help e (loop (cdr set)) m ...)))))
|
||
|
((_ e base (x is y) m ...)
|
||
|
(let ((x y)) (set-of-help e base m ...)))
|
||
|
((_ e base p m ...)
|
||
|
(if p (set-of-help e base m ...) base))))
|
||
|
|
||
|
;;; set-cons returns the original set y if x is already in y.
|
||
|
(define set-cons
|
||
|
(lambda (x y)
|
||
|
(if (memv x y)
|
||
|
y
|
||
|
(cons x y))))
|