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sugar/list.rkt

96 lines
3.4 KiB
Racket

#lang racket/base
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(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 (slicef-at xs pred [force? #f])
((list? procedure?) (boolean?) . ->* . (listof list?))
(cond
[(null? xs) null]
[force? (slicef-at (dropf xs (compose1 not pred)) pred)]
[else
(define-values (car-match others) (splitf-at xs pred))
(define-values (head tail) (splitf-at others (compose1 not pred)))
(cons (append (or car-match null) head) (slicef-at tail pred force?))]))
(require sugar/debug)
(define+provide/contract (slice-at xs len [force? #f])
((list? (and/c integer? positive?)) (boolean?) . ->* . (listof list?))
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(cond
[(equal? xs null) null]
[(len . > . (length xs)) (if force? null (list xs))]
[else (cons (take xs len) (slice-at (drop xs len) len force?))]))
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(define+provide/contract (filter-split xs split-test)
(list? predicate/c . -> . (listof list?))
(let loop ([xs (trimf xs split-test)] [acc '()])
(if (empty? xs)
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(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))])
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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?)
(define counter (make-hash))
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(for ([item (in-list (flatten x))])
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(hash-set! counter item (add1 (hash-ref counter item 0))))
counter)
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(define+provide/contract (members-unique? x)
((or/c list? vector? string?) . -> . boolean?)
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(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))]))
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(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)
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(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))
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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) '())]))
(provide values->list)
(define-syntax (values->list stx)
(syntax-case stx ()
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[(_ values-expr) #'(call-with-values (λ () values-expr) list)]))
(define+provide/contract (sublist xs i j)
(list? (and/c integer? (not/c negative?)) (and/c integer? (not/c negative?)) . -> . list?)
(cond
[(> j (length xs)) (error 'sublist (format "ending index ~a exceeds length of list" j))]
[(>= j i) (take (drop xs i) (- j i))]
[else (error 'sublist (format "starting index ~a is larger than ending index ~a" i j))]))