|
|
|
|
|
#lang racket/base
|
|
|
|
|
|
(require racket/list)
|
|
|
|
|
|
(provide (all-defined-out))
|
|
|
|
|
|
|
|
|
|
|
|
(module+ test (require rackunit))
|
|
|
|
|
|
|
|
|
|
|
|
(define (list-comparator xs ys)
|
|
|
|
|
|
;; For use in sort. Compares two lists element by element.
|
|
|
|
|
|
(cond
|
|
|
|
|
|
[(equal? xs ys) #f] ; elements are same, so no sort preference
|
|
|
|
|
|
[(and (null? xs) (not (null? ys))) #t] ; ys is longer, so #t
|
|
|
|
|
|
[(and (not (null? xs)) (null? ys)) #f] ; xs is longer, so #f makes it sort later
|
|
|
|
|
|
[else (let ([x (car xs)][y (car ys)])
|
|
|
|
|
|
(cond
|
|
|
|
|
|
[(equal? x y) (list-comparator (cdr xs) (cdr ys))]
|
|
|
|
|
|
[(and (real? x) (real? y)) (< x y)]
|
|
|
|
|
|
[(and (string? x) (string? y)) (string<? x y)]
|
|
|
|
|
|
[else (error 'list-comparator (format "Can’t compare ~v and ~v" x y))]))]))
|
|
|
|
|
|
|
|
|
|
|
|
(module+ test
|
|
|
|
|
|
(check-false (list-comparator null null))
|
|
|
|
|
|
(check-false (list-comparator (range 2) (range 2)))
|
|
|
|
|
|
(check-true (list-comparator (range 2) (range 4)))
|
|
|
|
|
|
(check-false (list-comparator (range 4) (range 2)))
|
|
|
|
|
|
(check-true (list-comparator '(1 1 "a") '(1 1 "b"))))
|
|
|
|
|
|
|
|
|
|
|
|
(define-syntax-rule (py-pop! xs)
|
|
|
|
|
|
(let ([i (last xs)])
|
|
|
|
|
|
(set! xs (drop-right xs 1))
|
|
|
|
|
|
i))
|
|
|
|
|
|
|
|
|
|
|
|
(module+ test
|
|
|
|
|
|
(let ([xs '(1 2 3)])
|
|
|
|
|
|
(check-equal? (py-pop! xs) 3)
|
|
|
|
|
|
(check-equal? xs '(1 2))))
|
|
|
|
|
|
|
|
|
|
|
|
(define-syntax-rule (py-append! xs x)
|
|
|
|
|
|
(set! xs `(,@xs ,x)))
|
|
|
|
|
|
|
|
|
|
|
|
(define-syntax-rule (py-extend! xs x)
|
|
|
|
|
|
(set! xs `(,@xs ,@x)))
|
|
|
|
|
|
|
|
|
|
|
|
(module+ test
|
|
|
|
|
|
(let ([xs '(1 2 3)])
|
|
|
|
|
|
(py-append! xs (range 2))
|
|
|
|
|
|
(check-equal? xs '(1 2 3 (0 1))))
|
|
|
|
|
|
(let ([xs '(1 2 3)])
|
|
|
|
|
|
(py-extend! xs (range 2))
|
|
|
|
|
|
(check-equal? xs '(1 2 3 0 1))))
|
