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sugar/list.rkt

72 lines
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Racket

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#lang racket/base
(require (for-syntax racket/base))
(require racket/list racket/set)
(require "define.rkt" "len.rkt" "coerce.rkt")
(define+provide/contract (trimf xs test-proc)
(list? procedure? . -> . list?)
(dropf-right (dropf xs test-proc) test-proc))
(define+provide/contract (list->slices xs len)
(list? integer? . -> . (listof list?))
(cond
[(equal? xs null) null]
[(len . > . (length xs)) (list xs)]
[else (cons (take xs len) (list->slices (drop xs len) len))]))
(define+provide/contract (filter-split xs split-test)
(list? predicate/c . -> . (listof list?))
(let loop ([xs (trimf xs split-test)] [acc '()])
(if (empty? xs)
(reverse acc) ; because accumulation is happening backward
(let-values ([(item rest)
;; drop matching elements from front
;; then split on nonmatching
;; = nonmatching item + other elements (which will start with matching)
(splitf-at (dropf xs split-test) (compose1 not split-test))])
(loop rest (cons item acc))))))
(define+provide/contract (frequency-hash x)
(list? . -> . hash?)
(define counter (make-hash))
(for ([item (flatten x)])
(hash-set! counter item (add1 (hash-ref counter item 0))))
counter)
(define+provide/contract (members-unique? x)
((or/c list? vector? string?) . -> . boolean?)
(cond
[(list? x) (= (len (remove-duplicates x)) (len x))]
[(vector? x) (->list x)]
[(string? x) (string->list x)]
[else (error (format "members-unique? cannot be determined for ~a" x))]))
(define+provide/contract (members-unique?/error x)
(any/c . -> . boolean?)
(define result (members-unique? x))
(if (not result)
(let* ([duplicate-keys (filter-not empty? (hash-map (frequency-hash x)
(λ(k v) (if (> v 1) k '()))))])
(error (string-append "members-unique? failed because " (if (= (len duplicate-keys) 1)
"item isnt"
"items arent") " unique:") duplicate-keys))
result))
;; for use inside quasiquote
;; instead of ,(when ...) use ,@(when/splice ...)
;; to avoid voids
(provide when/splice)
(define-syntax (when/splice stx)
(syntax-case stx ()
[(_ test body)
#'(if test (list body) '())]))