racket-ansi/rmacs/circular-list.rkt

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2014-12-22 22:14:13 +00:00
#lang racket/base
(provide circular-list?
circular-empty
circular-null?
circular-pair?
circular-cons
circular-car
circular-cdr
circular-length
circular-list-rotate-forward
circular-list-rotate-backward
list->circular-list
circular-list->list
circular-list-map
circular-list-filter
circular-list-remove
circular-list-memf
circular-list-replacef)
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(require racket/match)
(require (only-in racket/list splitf-at))
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(struct circular-list ([front #:mutable]
[back #:mutable]
) #:prefab)
(define circular-empty (circular-list '() '()))
(define (circular-null? xs)
(equal? xs circular-empty))
(define (circular-pair? xs)
(and (circular-list? xs)
(not (circular-null? xs))))
(define (circular-cons->cons xs)
(cons (circular-car xs)
(circular-cdr xs)))
(define (circular-cons* x xs)
(circular-list (cons x (circular-list-front xs)) (circular-list-back xs)))
(define-match-expander circular-cons
(syntax-rules ()
[(_ a d) (? circular-pair? (app circular-cons->cons (cons a d)))])
(syntax-rules ()
[(_ a d) (circular-cons* a d)]))
(define (prime! xs)
(match xs
[(circular-list '() back)
(set-circular-list-front! xs (reverse back))
(set-circular-list-back! xs '())]
[_ (void)])
xs)
(define (anti-prime! xs)
(match xs
[(circular-list front '())
(set-circular-list-front! xs '())
(set-circular-list-back! xs (reverse front))]
[_ (void)])
xs)
(define (circular-car xs)
(if (circular-null? xs)
(error 'circular-car "Empty circular list")
(car (circular-list-front (prime! xs)))))
(define (circular-cdr xs)
(if (circular-null? xs)
(error 'circular-cdr "Empty circular list")
(begin (prime! xs)
(circular-list (cdr (circular-list-front xs)) (circular-list-back xs)))))
(define (circular-length xs)
(+ (length (circular-list-front xs))
(length (circular-list-back xs))))
(define (circular-list-rotate-forward xs)
(if (circular-null? xs)
xs
(begin (prime! xs)
(circular-list (cdr (circular-list-front xs))
(cons (car (circular-list-front xs))
(circular-list-back xs))))))
(define (circular-list-rotate-backward xs)
(if (circular-null? xs)
xs
(begin (anti-prime! xs)
(circular-list (cons (car (circular-list-back xs))
(circular-list-front xs))
(cdr (circular-list-back xs))))))
(define (list->circular-list xs)
(circular-list xs '()))
(define (circular-list->list xs)
(append (circular-list-front xs) (reverse (circular-list-back xs))))
(define (map/reversed-order f xs)
(if (null? xs)
'()
(let ((tail (map/reversed-order f (cdr xs))))
(cons (f (car xs)) tail))))
(define (circular-list-map f xs)
(circular-list (map f (circular-list-front xs))
(map/reversed-order f (circular-list-back xs))))
;; WARNING: does not preserve order of evaluation wrt back
(define (circular-list-filter f xs)
(circular-list (filter f (circular-list-front xs))
(filter f (circular-list-back xs))))
(define (circular-list-remove item xs [comparison equal?])
(define new-front (remove item (circular-list-front xs) comparison))
(if (= (length new-front) (length (circular-list-front xs)))
(circular-list (circular-list-front xs)
(reverse (remove item (reverse (circular-list-back xs)) comparison)))
(circular-list new-front (circular-list-back xs))))
(define (circular-list-memf f xs)
(let loop ((seen '()) (xs xs))
(if (circular-null? xs)
#f
(let ((a (circular-car xs)))
(if (f a)
(circular-list (circular-list-front xs)
(append seen (circular-list-back xs)))
(loop (cons a seen) (circular-cdr xs)))))))
(define (circular-list-replacef xs finder replacer)
(define (rejecter e) (not (finder e)))
(define-values (head tail) (splitf-at (circular-list-front xs) rejecter))
(if (null? tail)
(let-values (((head tail) (splitf-at (reverse (circular-list-back xs)) rejecter)))
(if (null? tail)
xs
(circular-list (circular-list-front xs)
(reverse (append head (replacer (car tail)) (cdr tail))))))
(circular-list (append head (replacer (car tail)) (cdr tail))
(circular-list-back xs))))
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(module+ test
(require rackunit)
(define (check-abcdef abcdef)
(define bcdefa (circular-list-rotate-forward abcdef))
(check-equal? (circular-length abcdef) 6)
(check-equal? (circular-list->list abcdef) '(a b c d e f))
(check-equal? (circular-list->list bcdefa) '(b c d e f a))
(check-equal? (circular-list->list (for/fold [(xs abcdef)] [(i (circular-length abcdef))]
(circular-list-rotate-forward xs)))
(circular-list->list abcdef))
(check-equal? (circular-list->list (for/fold [(xs abcdef)] [(i (circular-length abcdef))]
(circular-list-rotate-backward xs)))
(circular-list->list abcdef)))
(check-abcdef (circular-list '(a b c) '(f e d)))
(check-abcdef (circular-list '(a b c d e f) '()))
(check-abcdef (circular-list '() '(f e d c b a)))
(check-equal? (circular-list->list (circular-list-replacef (circular-list '(a b c) '(f e d))
(lambda (x) (eq? x 'e))
(lambda (x) (list 111))))
'(a b c d 111 f))
(check-equal? (circular-list->list (circular-list-replacef (circular-list '(a b c) '(f e d))
(lambda (x) (eq? x 'e))
(lambda (x) (list 111 222))))
'(a b c d 111 222 f))
(check-equal? (circular-list->list (circular-list-replacef (circular-list '(a b c) '(f e d))
(lambda (x) (eq? x 'b))
(lambda (x) (list 111))))
'(a 111 c d e f))
(check-equal? (circular-list->list (circular-list-replacef (circular-list '(a b c) '(f e d))
(lambda (x) (eq? x 'b))
(lambda (x) (list 111 222))))
'(a 111 222 c d e f))
(check-equal? (circular-list->list (circular-list-replacef (circular-list '(a b c) '(f e d))
(lambda (x) (eq? x 'x))
(lambda (x) (list 111 222))))
'(a b c d e f))
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(check-equal? (match (circular-cons 1 circular-empty)
[(circular-cons a d) (cons a d)])
(cons 1 circular-empty))
(check-equal? (match (circular-list-rotate-forward (circular-cons 1 circular-empty))
[(circular-cons a d) (cons a d)])
(cons 1 circular-empty))
(check-equal? (match (circular-list-rotate-forward
(circular-cons 1 (circular-cons 2 circular-empty)))
[(circular-cons a d) (cons a (circular-list->list d))])
(list 2 1))
(check-equal? (circular-list->list (circular-list-remove 2 (circular-list '(1 2 3) '(6 5 4))))
'(1 3 4 5 6))
(check-equal? (circular-list->list (circular-list-remove 2 (circular-list '(1) '(6 5 4 3 2))))
'(1 3 4 5 6))
(check-equal? (circular-list->list (circular-list-remove 2 (circular-list '(1 2 3 2) '(6 5 2 4))))
'(1 3 2 4 2 5 6))
(check-equal? (circular-list->list (circular-list-remove 2 (circular-list '(1) '(6 5 2 4 2 3 2))))
'(1 3 2 4 2 5 6)))