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;; JACAL: Symbolic Mathematics System. -*-scheme-*-
;; Copyright 1989, 1990, 1991, 1992, 1993, 1995 Aubrey Jaffer.
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or (at
;; your option) any later version.
;;
;; This program is distributed in the hope that it will be useful, but
;; WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program; if not, write to the Free Software
;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
(require 'common-list-functions)
(require 'hash-table) ; for memon
;;; =================== Memoize procedure calls ===================
;;; From Norvig "Artificial Intelligence Programming"
;;; Examples:
;;; (define fib
;;; (memon (lambda (n)
;;; (if (<= n 1) 1
;;; (+ (fib (+ -1 n)) (fib (+ -2 n)))))))
;;;
;;; (define sum
;;; (memon (lambda (x y)
;;; (+ x y))))
;;;
(define (memon fn)
(let ((table (make-hash-table 100))
(gethash (hash-inquirer equal?))
(puthash (hash-associator equal?)))
(lambda x
(let ((val (gethash table x)))
(if val
val
(let ((fx (apply fn x)))
(puthash table x fx)
fx))))))
(define (factorial n)
(define (fact i acc)
(if (< i 2) acc (fact (+ -1 i) (* acc i))))
(fact n 1))
(define (cart-prod choices)
(if (null? choices)
'(())
(let* ((choice (car choices)))
(apply append
(map (lambda (tuple)
(map (lambda (elt)
(cons elt tuple))
choice))
(cart-prod (cdr choices)))))))
;;;; From Mike Thomas:
;;; Return all the unique subsets of size n obtainable from the list l
(define (combinations l n)
(define (combs1 l1 l2 n acc)
(let* ((l1l (length l1))
(l2l (length l2))
(sumls (+ l1l l2l)))
(cond ((< sumls n) acc)
((= sumls n) (append acc (list (append l1 l2))))
((= l1l (+ -1 n))
(append acc (map (lambda (x) (append l1 (list x))) l2)))
(else (apply append
(map (lambda (x y)
(combs1 (append l1 (list x)) y n acc))
l2 (make-ends (cdr l2) '())))))))
(define (make-ends l acc)
(if (null? l)
(append acc '(()))
(make-ends (cdr l) (append acc (list l)))))
(combs1 '() l n '()))
;;; (UNIQUES L) removes any element in each member of a list of lists
;;; that is present in any other member of the list of lists,
;;; preserving order.
;;; (BUILD-UNIQUE-ITEMS L1 L2) builds a list of the members of l1
;;; which are not members of each list in the list l2.
(define (uniques l)
(define (unis a b c)
(cond ((null? b) c)
(else (unis (cons a (list (car b)))
(cdr b)
(let ((l1 (car b))
(l2 (append a (cdr b))))
(for-each
(lambda (x)
(if (some (lambda (sl) (member x sl)) l2)
(set! l1 (remove x l1)))) l1)
(append
c (list l1)))))))
(unis '() l '()))
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