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