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[bpt/guile.git] / test-suite / tests / srfi-1.test

;;;; srfi-1.test --- Test suite for Guile's SRFI-1 functions. -*- scheme -*-
;;;;
;;;; Copyright 2003 Free Software Foundation, Inc.
;;;;
;;;; 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 2, 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 software; see the file COPYING.  If not, write to
;;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
;;;; Boston, MA 02111-1307 USA

(use-modules (srfi srfi-1)
	     (test-suite lib))

(define (ref-delete x lst . proc)
  "Reference implemenation of srfi-1 `delete'."
  (set! proc (if (null? proc) equal? (car proc)))
  (do ((ret '())
       (lst lst (cdr lst)))
      ((null? lst)
       (reverse! ret))
    (if (not (proc x (car lst)))
	(set! ret (cons (car lst) ret)))))

(define (ref-delete-duplicates lst . proc)
  "Reference implemenation of srfi-1 `delete-duplicates'."
  (set! proc (if (null? proc) equal? (car proc)))
  (if (null? lst)
      '()
      (do ((keep '()))
	  ((null? lst)
	   (reverse! keep))
	(let ((elem (car lst)))
	  (set! keep (cons elem keep))
	  (set! lst  (ref-delete elem lst proc))))))


;;
;; append-map
;;

(with-test-prefix "append-map"

  (with-test-prefix "one list"

    (pass-if "()"
      (equal? '() (append-map noop '(()))))

    (pass-if "(1)"
      (equal? '(1) (append-map noop '((1)))))

    (pass-if "(1 2)"
      (equal? '(1 2) (append-map noop '((1 2)))))

    (pass-if "() ()"
      (equal? '() (append-map noop '(() ()))))

    (pass-if "() (1)"
      (equal? '(1) (append-map noop '(() (1)))))

    (pass-if "() (1 2)"
      (equal? '(1 2) (append-map noop '(() (1 2)))))

    (pass-if "(1) (2)"
      (equal? '(1 2) (append-map noop '((1) (2)))))

    (pass-if "(1 2) ()"
      (equal? '(1 2) (append-map noop '(() (1 2))))))

  (with-test-prefix "two lists"

    (pass-if "() / 9"
      (equal? '() (append-map noop '(()) '(9))))

    (pass-if "(1) / 9"
      (equal? '(1) (append-map noop '((1)) '(9))))

    (pass-if "() () / 9 9"
      (equal? '() (append-map noop '(() ()) '(9 9))))

    (pass-if "(1) (2) / 9"
      (equal? '(1) (append-map noop '((1) (2)) '(9))))

    (pass-if "(1) (2) / 9 9"
      (equal? '(1 2) (append-map noop '((1) (2)) '(9 9))))))
  
;;
;; concatenate and concatenate!
;;

(let ()	
  (define (common-tests concatenate-proc unmodified?)
    (define (try lstlst want)
      (let ((lstlst-copy (copy-tree lstlst))
	    (got         (concatenate-proc lstlst)))
	(if unmodified?
	    (if (not (equal? lstlst lstlst-copy))
		(error "input lists modified")))
	(equal? got want)))
    
    (pass-if-exception "too few args" exception:wrong-num-args
      (concatenate-proc))
    
    (pass-if-exception "too many args" exception:wrong-num-args
      (concatenate-proc '() '()))
    
    (pass-if "no lists"
      (try '() '()))
    
    (pass-if (try '((1))       '(1)))
    (pass-if (try '((1 2))     '(1 2)))
    (pass-if (try '(() (1))    '(1)))
    (pass-if (try '(() () (1)) '(1)))
    
    (pass-if (try '((1) (2)) '(1 2)))
    (pass-if (try '(() (1 2)) '(1 2)))
    
    (pass-if (try '((1) 2)           '(1 . 2)))
    (pass-if (try '((1) (2) 3)       '(1 2 . 3)))
    (pass-if (try '((1) (2) (3 . 4)) '(1 2 3 . 4)))
    )
  
  (with-test-prefix "concatenate"
    (common-tests concatenate #t))
  
  (with-test-prefix "concatenate!"
    (common-tests concatenate! #f)))

;;
;; count
;;

(with-test-prefix "count"
  (pass-if-exception "no args" exception:wrong-num-args
    (count))
  
  (pass-if-exception "one arg" exception:wrong-num-args
    (count noop))
  
  (with-test-prefix "one list"
    (define (or1 x)
      x)
    
    (pass-if "empty list" (= 0 (count or1 '())))
    
    (pass-if-exception "pred arg count 0" exception:wrong-type-arg
      (count (lambda () x) '(1 2 3)))
    (pass-if-exception "pred arg count 2" exception:wrong-type-arg
      (count (lambda (x y) x) '(1 2 3)))
    
    (pass-if-exception "improper 1" exception:wrong-type-arg
      (count or1 1))
    (pass-if-exception "improper 2" exception:wrong-type-arg
      (count or1 '(1 . 2)))
    (pass-if-exception "improper 3" exception:wrong-type-arg
      (count or1 '(1 2 . 3)))
    
    (pass-if (= 0 (count or1 '(#f))))
    (pass-if (= 1 (count or1 '(#t))))
    
    (pass-if (= 0 (count or1 '(#f #f))))
    (pass-if (= 1 (count or1 '(#f #t))))
    (pass-if (= 1 (count or1 '(#t #f))))
    (pass-if (= 2 (count or1 '(#t #t))))
    
    (pass-if (= 0 (count or1 '(#f #f #f))))
    (pass-if (= 1 (count or1 '(#f #f #t))))
    (pass-if (= 1 (count or1 '(#t #f #f))))
    (pass-if (= 2 (count or1 '(#t #f #t))))
    (pass-if (= 3 (count or1 '(#t #t #t)))))
  
  (with-test-prefix "two lists"
    (define (or2 x y)
      (or x y))
    
    (pass-if "arg order"
      (= 1 (count (lambda (x y)
		    (and (= 1 x)
			 (= 2 y)))
		  '(1) '(2))))
    
    (pass-if "empty lists" (= 0 (count or2 '() '())))
    
    (pass-if-exception "pred arg count 0" exception:wrong-type-arg
      (count (lambda () #t) '(1 2 3) '(1 2 3)))
    (pass-if-exception "pred arg count 1" exception:wrong-type-arg
      (count (lambda (x) x) '(1 2 3) '(1 2 3)))
    (pass-if-exception "pred arg count 3" exception:wrong-type-arg
      (count (lambda (x y z) x) '(1 2 3) '(1 2 3)))
    
    (pass-if-exception "improper first 1" exception:wrong-type-arg
      (count or2 1 '(1 2 3)))
    (pass-if-exception "improper first 2" exception:wrong-type-arg
      (count or2 '(1 . 2) '(1 2 3)))
    (pass-if-exception "improper first 3" exception:wrong-type-arg
      (count or2 '(1 2 . 3) '(1 2 3)))
    
    (pass-if-exception "improper second 1" exception:wrong-type-arg
      (count or2 '(1 2 3) 1))
    (pass-if-exception "improper second 2" exception:wrong-type-arg
      (count or2 '(1 2 3) '(1 . 2)))
    (pass-if-exception "improper second 3" exception:wrong-type-arg
      (count or2 '(1 2 3) '(1 2 . 3)))
    
    (pass-if (= 0 (count or2 '(#f) '(#f))))
    (pass-if (= 1 (count or2 '(#t) '(#f))))
    (pass-if (= 1 (count or2 '(#f) '(#t))))
    
    (pass-if (= 0 (count or2 '(#f #f) '(#f #f))))
    (pass-if (= 1 (count or2 '(#t #f) '(#t #f))))
    (pass-if (= 2 (count or2 '(#t #t) '(#f #f))))
    (pass-if (= 2 (count or2 '(#t #f) '(#f #t))))
    
    (with-test-prefix "stop shortest"
      (pass-if (= 2 (count or2 '(#t #f #t) '(#f #t))))
      (pass-if (= 2 (count or2 '(#t #f #t #t) '(#f #t))))
      (pass-if (= 2 (count or2 '(#t #f) '(#f #t #t))))
      (pass-if (= 2 (count or2 '(#t #f) '(#f #t #t #t))))))
  
  (with-test-prefix "three lists"
    (define (or3 x y z)
      (or x y z))
    
    (pass-if "arg order"
      (= 1 (count (lambda (x y z)
		    (and (= 1 x)
			 (= 2 y)
			 (= 3 z)))
		  '(1) '(2) '(3))))
    
    (pass-if "empty lists" (= 0 (count or3 '() '() '())))
    
    ;; currently bad pred argument gives wrong-num-args when 3 or more
    ;; lists, as opposed to wrong-type-arg for 1 or 2 lists
    (pass-if-exception "pred arg count 0" exception:wrong-num-args
      (count (lambda () #t) '(1 2 3) '(1 2 3) '(1 2 3)))
    (pass-if-exception "pred arg count 2" exception:wrong-num-args
      (count (lambda (x y) x) '(1 2 3) '(1 2 3)'(1 2 3) ))
    (pass-if-exception "pred arg count 4" exception:wrong-num-args
      (count (lambda (w x y z) x) '(1 2 3) '(1 2 3) '(1 2 3)))
    
    (pass-if-exception "improper first 1" exception:wrong-type-arg
      (count or3 1 '(1 2 3) '(1 2 3)))
    (pass-if-exception "improper first 2" exception:wrong-type-arg
      (count or3 '(1 . 2) '(1 2 3) '(1 2 3)))
    (pass-if-exception "improper first 3" exception:wrong-type-arg
      (count or3 '(1 2 . 3) '(1 2 3) '(1 2 3)))
    
    (pass-if-exception "improper second 1" exception:wrong-type-arg
      (count or3 '(1 2 3) 1 '(1 2 3)))
    (pass-if-exception "improper second 2" exception:wrong-type-arg
      (count or3 '(1 2 3) '(1 . 2) '(1 2 3)))
    (pass-if-exception "improper second 3" exception:wrong-type-arg
      (count or3 '(1 2 3) '(1 2 . 3) '(1 2 3)))
    
    (pass-if-exception "improper third 1" exception:wrong-type-arg
      (count or3 '(1 2 3) '(1 2 3) 1))
    (pass-if-exception "improper third 2" exception:wrong-type-arg
      (count or3 '(1 2 3) '(1 2 3) '(1 . 2)))
    (pass-if-exception "improper third 3" exception:wrong-type-arg
      (count or3 '(1 2 3) '(1 2 3) '(1 2 . 3)))
    
    (pass-if (= 0 (count or3 '(#f) '(#f) '(#f))))
    (pass-if (= 1 (count or3 '(#t) '(#f) '(#f))))
    (pass-if (= 1 (count or3 '(#f) '(#t) '(#f))))
    (pass-if (= 1 (count or3 '(#f) '(#f) '(#t))))
    
    (pass-if (= 0 (count or3 '(#f #f) '(#f #f) '(#f #f))))
    
    (pass-if (= 1 (count or3 '(#t #f) '(#f #f) '(#f #f))))
    (pass-if (= 1 (count or3 '(#f #t) '(#f #f) '(#f #f))))
    (pass-if (= 1 (count or3 '(#f #f) '(#t #f) '(#f #f))))
    (pass-if (= 1 (count or3 '(#f #f) '(#f #t) '(#f #f))))
    (pass-if (= 1 (count or3 '(#f #f) '(#f #f) '(#t #f))))
    (pass-if (= 1 (count or3 '(#f #f) '(#f #f) '(#f #t))))
    
    (pass-if (= 2 (count or3 '(#t #t) '(#f #f) '(#f #f))))
    (pass-if (= 2 (count or3 '(#f #f) '(#t #t) '(#f #f))))
    (pass-if (= 2 (count or3 '(#f #f) '(#f #f) '(#t #t))))
    (pass-if (= 2 (count or3 '(#f #f) '(#t #f) '(#f #t))))
    
    (with-test-prefix "stop shortest"
      (pass-if (= 0 (count or3 '() '(#t #t #t) '(#t #t))))
      (pass-if (= 0 (count or3 '(#t #t #t) '() '(#t #t))))
      (pass-if (= 0 (count or3 '(#t #t #t) '(#t #t) '())))
      
      (pass-if (= 1 (count or3 '(#t) '(#t #t #t) '(#t #t))))
      (pass-if (= 1 (count or3 '(#t #t #t) '(#t) '(#t #t))))
      (pass-if (= 1 (count or3 '(#t #t #t) '(#t #t) '(#t)))))))

;;
;; delete and delete!
;;

(let ()	
  ;; Call (PROC lst) for all lists of length up to 6, with all combinations
  ;; of elements to be retained or deleted.  Elements to retain are numbers,
  ;; 0 upwards.  Elements to be deleted are #f.
  (define (test-lists proc)
    (do ((n 0 (1+ n)))
	((>= n 6))
      (do ((limit (ash 1 n))
	   (i 0 (1+ i)))
	  ((>= i limit))
	(let ((lst '()))
	  (do ((bit 0 (1+ bit)))
	      ((>= bit n))
	    (set! lst  (cons (if (logbit? bit i) bit #f) lst)))
	  (proc lst)))))
  
  (define (common-tests delete-proc)
    (pass-if-exception "too few args" exception:wrong-num-args
      (delete-proc 0))
    
    (pass-if-exception "too many args" exception:wrong-num-args
      (delete-proc 0 '() equal? 99))
    
    (pass-if "empty"
      (eq? '() (delete-proc 0 '())))
    
    (pass-if "equal? (the default)"
      (equal? '((1) (3))
	      (delete-proc '(2) '((1) (2) (3)))))
    
    (pass-if "eq?"
      (equal? '((1) (2) (3))
	      (delete-proc '(2) '((1) (2) (3)) eq?)))
    
    (pass-if "called arg order"
      (equal? '(1 2 3)
	      (delete-proc 3 '(1 2 3 4 5) <))))
  
  (with-test-prefix "delete"
    (common-tests delete)
    
    (test-lists
     (lambda (lst)
       (let ((lst-copy (list-copy lst)))
	 (with-test-prefix lst-copy
	   (pass-if "result"
	     (equal? (delete     #f lst)
		     (ref-delete #f lst)))
	   (pass-if "non-destructive"
	     (equal? lst-copy lst)))))))  
  
  (with-test-prefix "delete!"
    (common-tests delete!)
    
    (test-lists
     (lambda (lst)
       (pass-if lst
	 (equal? (delete!    #f lst)
		 (ref-delete #f lst)))))))

;;
;; delete-duplicates and delete-duplicates!
;;

(let ()	
  ;; Call (PROC lst) for all lists of length 1 <= n <= 4, with all
  ;; combinations of numbers 1 to n in the elements
  (define (test-lists proc)
    (do ((n 1 (1+ n)))
	((> n 4))
      (do ((limit (integer-expt n n))
	   (i 0 (1+ i)))
	  ((>= i limit))
	(let ((lst '()))
	  (do ((j 0 (1+ j))
	       (rem i (quotient rem n)))
	      ((>= j n))
	    (set! lst (cons (remainder rem n) lst)))
	  (proc lst)))))

  (define (common-tests delete-duplicates-proc)
    (pass-if-exception "too few args" exception:wrong-num-args
      (delete-duplicates-proc))
    
    (pass-if-exception "too many args" exception:wrong-num-args
      (delete-duplicates-proc '() equal? 99))
    
    (pass-if "empty"
      (eq? '() (delete-duplicates-proc '())))
    
    (pass-if "equal? (the default)"
      (equal? '((2))
	      (delete-duplicates-proc '((2) (2) (2)))))
    
    (pass-if "eq?"
      (equal? '((2) (2) (2))
	      (delete-duplicates-proc '((2) (2) (2)) eq?)))

    (pass-if "called arg order"
      (let ((ok #t))
	(delete-duplicates-proc '(1 2 3 4 5)
				(lambda (x y)
				  (if (> x y)
				      (set! ok #f))
				  #f))
	ok)))
  
  (with-test-prefix "delete-duplicates"
    (common-tests delete-duplicates)
    
    (test-lists
     (lambda (lst)
       (let ((lst-copy (list-copy lst)))
	 (with-test-prefix lst-copy
	   (pass-if "result"
	     (equal? (delete-duplicates     lst)
		     (ref-delete-duplicates lst)))
	   (pass-if "non-destructive"
	     (equal? lst-copy lst)))))))  
  
  (with-test-prefix "delete-duplicates!"
    (common-tests delete-duplicates!)
    
    (test-lists
     (lambda (lst)
       (pass-if lst
	 (equal? (delete-duplicates!    lst)
		 (ref-delete-duplicates lst)))))))

;;
;; drop
;;

(with-test-prefix "drop"
  
  (pass-if "'() 0"
    (null? (drop '() 0)))
  
  (pass-if "'(a) 0"
    (let ((lst '(a)))
      (eq? lst
	   (drop lst 0))))
  
  (pass-if "'(a b) 0"
    (let ((lst '(a b)))
      (eq? lst
	   (drop lst 0))))
  
  (pass-if "'(a) 1"
    (let ((lst '(a)))
      (eq? (cdr lst)
	   (drop lst 1))))
  
  (pass-if "'(a b) 1"
    (let ((lst '(a b)))
      (eq? (cdr lst)
	   (drop lst 1))))
  
  (pass-if "'(a b) 2"
    (let ((lst '(a b)))
      (eq? (cddr lst)
	   (drop lst 2))))
  
  (pass-if "'(a b c) 1"
    (let ((lst '(a b c)))
      (eq? (cddr lst)
	   (drop lst 2))))
  
  (pass-if "circular '(a) 0"
    (let ((lst (circular-list 'a)))
      (eq? lst
	   (drop lst 0))))
  
  (pass-if "circular '(a) 1"
    (let ((lst (circular-list 'a)))
      (eq? lst
	   (drop lst 1))))
  
  (pass-if "circular '(a) 2"
    (let ((lst (circular-list 'a)))
      (eq? lst
	   (drop lst 1))))
  
  (pass-if "circular '(a b) 1"
    (let ((lst (circular-list 'a)))
      (eq? (cdr lst)
	   (drop lst 0))))
  
  (pass-if "circular '(a b) 2"
    (let ((lst (circular-list 'a)))
      (eq? lst
	   (drop lst 1))))
  
  (pass-if "circular '(a b) 5"
    (let ((lst (circular-list 'a)))
      (eq? (cdr lst)
	   (drop lst 5))))
  
  (pass-if "'(a . b) 1"
    (eq? 'b
	 (drop '(a . b) 1)))
  
  (pass-if "'(a b . c) 1"
    (equal? 'c
	    (drop '(a b . c) 2))))

;;
;; filter-map
;;

(with-test-prefix "filter-map"

  (with-test-prefix "one list"
    (pass-if "(1)"
      (equal? '(1) (filter-map noop '(1))))

    (pass-if "(#f)"
      (equal? '() (filter-map noop '(#f))))

    (pass-if "(1 2)"
      (equal? '(1 2) (filter-map noop '(1 2))))

    (pass-if "(#f 2)"
      (equal? '(2) (filter-map noop '(#f 2))))

    (pass-if "(#f #f)"
      (equal? '() (filter-map noop '(#f #f))))

    (pass-if "(1 2 3)"
      (equal? '(1 2 3) (filter-map noop '(1 2 3))))

    (pass-if "(#f 2 3)"
      (equal? '(2 3) (filter-map noop '(#f 2 3))))

    (pass-if "(1 #f 3)"
      (equal? '(1 3) (filter-map noop '(1 #f 3))))

    (pass-if "(1 2 #f)"
      (equal? '(1 2) (filter-map noop '(1 2 #f)))))

  (with-test-prefix "two lists"
    (pass-if "(1 2 3) (4 5 6)"
      (equal? '(1 2 3) (filter-map noop '(1 2 3) '(4 5 6))))

    (pass-if "(#f 2 3) (4 5)"
      (equal? '(2) (filter-map noop '(#f 2 3) '(4 5))))

    (pass-if "(4 #f) (1 2 3)"
      (equal? '(4) (filter-map noop '(4 #f) '(1 2 3))))))
  
;;
;; length+
;;

(with-test-prefix "length+"
  (pass-if-exception "too few args" exception:wrong-num-args
    (length+))
  (pass-if-exception "too many args" exception:wrong-num-args
    (length+ 123 456))
  (pass-if (= 0 (length+ '())))
  (pass-if (= 1 (length+ '(x))))
  (pass-if (= 2 (length+ '(x y))))
  (pass-if (= 3 (length+ '(x y z))))
  (pass-if (not (length+ (circular-list 1))))
  (pass-if (not (length+ (circular-list 1 2))))
  (pass-if (not (length+ (circular-list 1 2 3)))))

;;
;; list-copy
;;

(with-test-prefix "list-copy"
  (pass-if (equal? '()          (list-copy '())))
  (pass-if (equal? '(1 2)       (list-copy '(1 2))))
  (pass-if (equal? '(1 2 3)     (list-copy '(1 2 3))))
  (pass-if (equal? '(1 2 3 4)   (list-copy '(1 2 3 4))))
  (pass-if (equal? '(1 2 3 4 5) (list-copy '(1 2 3 4 5))))
  
  ;; improper lists can be copied
  (pass-if (equal? 1              (list-copy 1)))
  (pass-if (equal? '(1 . 2)       (list-copy '(1 . 2))))
  (pass-if (equal? '(1 2 . 3)     (list-copy '(1 2 . 3))))
  (pass-if (equal? '(1 2 3 . 4)   (list-copy '(1 2 3 . 4))))
  (pass-if (equal? '(1 2 3 4 . 5) (list-copy '(1 2 3 4 . 5)))))

;;
;; take
;;

(with-test-prefix "take"
  
  (pass-if "'() 0"
    (null? (take '() 0)))
  
  (pass-if "'(a) 0"
    (null? (take '(a) 0)))
  
  (pass-if "'(a b) 0"
    (null? (take '() 0)))
  
  (pass-if "'(a b c) 0"
    (null? (take '() 0)))
  
  (pass-if "'(a) 1"
    (let* ((lst '(a))
	   (got (take lst 1)))
      (and (equal? '(a) got)
	   (not (eq? lst got)))))
  
  (pass-if "'(a b) 1"
    (equal? '(a)
	    (take '(a b) 1)))
  
  (pass-if "'(a b c) 1"
    (equal? '(a)
	    (take '(a b c) 1)))
  
  (pass-if "'(a b) 2"
    (let* ((lst '(a b))
	   (got (take lst 2)))
      (and (equal? '(a b) got)
	   (not (eq? lst got)))))
  
  (pass-if "'(a b c) 2"
    (equal? '(a b)
	    (take '(a b c) 2)))
  
  (pass-if "circular '(a) 0"
    (equal? '()
	    (take (circular-list 'a) 0)))
  
  (pass-if "circular '(a) 1"
    (equal? '(a)
	    (take (circular-list 'a) 1)))
  
  (pass-if "circular '(a) 2"
    (equal? '(a a)
	    (take (circular-list 'a) 2)))
  
  (pass-if "circular '(a b) 5"
    (equal? '(a b a b a)
	    (take (circular-list 'a 'b) 5)))
  
  (pass-if "'(a . b) 1"
    (equal? '(a)
	    (take '(a . b) 1)))
  
  (pass-if "'(a b . c) 1"
    (equal? '(a)
	    (take '(a b . c) 1)))
  
  (pass-if "'(a b . c) 2"
    (equal? '(a b)
	    (take '(a b . c) 2))))

;;
;; partition
;;

(define (test-partition pred list kept-good dropped-good)
  (call-with-values (lambda ()
			(partition pred list))
      (lambda (kept dropped)
	(and (equal? kept kept-good)
	     (equal? dropped dropped-good)))))

(with-test-prefix "partition"
		  
  (pass-if "with dropped tail"
    (test-partition even? '(1 2 3 4 5 6 7)
		    '(2 4 6) '(1 3 5 7)))

  (pass-if "with kept tail"
    (test-partition even? '(1 2 3 4 5 6)
		    '(2 4 6) '(1 3 5)))

  (pass-if "with everything dropped"
    (test-partition even? '(1 3 5 7)
		    '() '(1 3 5 7)))

  (pass-if "with everything kept"
    (test-partition even? '(2 4 6)
		    '(2 4 6) '()))

  (pass-if "with empty list"
    (test-partition even? '()
		    '() '()))

  (pass-if "with reasonably long list"
    ;; the old implementation from SRFI-1 reference implementation
    ;; would signal a stack-overflow for a list of only 500 elements!
    (call-with-values (lambda ()
			(partition even?
				   (make-list 10000 1)))
      (lambda (even odd)
	(and (= (length odd) 10000)
	     (= (length even) 0))))))