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sugar/list.rkt

189 lines
7.8 KiB
Racket

#lang racket/base
(require (for-syntax racket/base) racket/list "define.rkt")
(define (list-of-lists? xs) (and (list? xs) (andmap list? xs)))
(define (index? x) (and (integer? x) (not (negative? x))))
(define increasing-nonnegative-list? (λ(x) (and (list? x) (or (empty? x)
(apply < -1 x)))))
(define (integers? x) (and (list? x) (andmap integer? x)))
(define+provide+safe (trimf xs test-proc)
(list? procedure? . -> . list?)
(dropf-right (dropf xs test-proc) test-proc))
(define+provide+safe (slicef xs pred)
(list? procedure? . -> . list-of-lists?)
(define-values (last-list list-of-lists last-negating)
(for/fold ([current-list empty]
[list-of-lists empty]
[negating? #f])
([x (in-list xs)])
(define current-pred (if negating? (λ (x) (not (pred x))) pred))
(if (current-pred x)
(values (cons x current-list) list-of-lists negating?)
(values (cons x null) (if (not (empty? current-list))
(cons (reverse current-list) list-of-lists)
list-of-lists) (not negating?)))))
(reverse (cons (reverse last-list) list-of-lists)))
(define+provide+safe (slicef-at xs pred [force? #f])
((list? procedure?) (boolean?) . ->* . list-of-lists?)
(define-values (last-list list-of-lists)
(for/fold
([current-list empty][list-of-lists empty])
([x (in-list xs)])
(if (pred x)
(values (cons x null) (if (not (empty? current-list))
(cons (reverse current-list) list-of-lists)
list-of-lists))
(values (cons x current-list) list-of-lists))))
(let ([list-of-lists (reverse (if (empty? last-list)
list-of-lists
(cons (reverse last-list) list-of-lists)))])
(if (and force? (not (empty? list-of-lists)) (not (pred (caar list-of-lists))))
(cdr list-of-lists)
list-of-lists)))
(define+provide+safe (slicef-after xs pred)
(list? procedure? . -> . list-of-lists?)
(define-values (last-list list-of-lists)
(for/fold ([current-list empty][list-of-lists empty])
([x (in-list xs)])
(if (pred x)
(values empty (cons (reverse (cons x current-list)) list-of-lists))
(values (cons x current-list) list-of-lists))))
(reverse (if (empty? last-list)
list-of-lists
(cons (reverse last-list) list-of-lists))))
(define+provide+safe (slice-at xs len [force? #f])
((list? (and/c integer? positive?)) (boolean?) . ->* . list-of-lists?)
(define-values (last-list list-of-lists)
(for/fold ([current-list empty][list-of-lists empty])
([x (in-list xs)][i (in-naturals)])
(if (= (modulo (add1 i) len) 0)
(values empty (cons (reverse (cons x current-list)) list-of-lists))
(values (cons x current-list) list-of-lists))))
(reverse (if (or (empty? last-list) (and force? (not (= len (length last-list)))))
list-of-lists
(cons (reverse last-list) list-of-lists))))
(define+provide+safe (filter-split xs pred)
(list? predicate/c . -> . list-of-lists?)
(define-values (last-list list-of-lists)
(for/fold ([current-list empty][list-of-lists empty])
([x (in-list xs)])
(if (pred x)
(values empty (if (not (empty? current-list))
(cons (reverse current-list) list-of-lists)
list-of-lists))
(values (cons x current-list) list-of-lists))))
(reverse (if (not (empty? last-list))
(cons (reverse last-list) list-of-lists)
list-of-lists)))
(define+provide+safe (frequency-hash xs)
(list? . -> . hash?)
(define counter (make-hash))
(for ([item (in-list xs)])
(hash-update! counter item (λ(v) (add1 v)) (λ _ 0)))
counter)
(define (->list x)
(cond
[(list? x) x]
[(vector? x) (vector->list x)]
[(string? x) (string->list x)]
[else (error '->list)]))
(define+provide+safe (members-unique? x)
((or/c list? vector? string?) . -> . boolean?)
(let ([x (->list x)])
(cond
[(list? x) (= (length (remove-duplicates x)) (length x))]
[else (error (format "members-unique? cannot be determined for ~a" x))])))
(define+provide+safe (members-unique?/error x)
((or/c list? vector? string?) . -> . boolean?)
(define result (members-unique? x))
(if (not result)
(let* ([duplicate-keys (filter-not empty? (hash-map (frequency-hash (->list x))
(λ(element freq) (if (> freq 1) element '()))))])
(error (string-append "members-unique? failed because " (if (= (length duplicate-keys) 1)
"item isn't"
"items aren't") " unique:") duplicate-keys))
result))
(provide+safe values->list)
(define-syntax (values->list stx)
(syntax-case stx ()
[(_ values-expr) #'(call-with-values (λ () values-expr) list)]))
(define+provide+safe (sublist xs i j)
(list? index? index? . -> . 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))]))
(define+provide+safe (break-at xs bps)
(list? any/c . -> . list-of-lists?)
(let ([bps (if (list? bps) bps (list bps))]) ; coerce bps to list
(when (ormap (λ(bp) (>= bp (length xs))) bps)
(error 'break-at (format "breakpoint in ~v is greater than or equal to input list length = ~a" bps (length xs))))
(when (not (increasing-nonnegative-list? bps))
(raise-argument-error 'break-at "increasing-nonnegative-list?" bps))
;; easier to do back to front, because then the list index for each item won't change during the recursion
;; cons a zero onto bps (which may already start with zero) and then use that as the terminating condition
;; because breaking at zero means we've reached the start of the list
(reverse (let loop ([xs xs][bps (reverse (cons 0 bps))])
(if (= (car bps) 0)
(cons xs null) ; return whatever's left, because no more splits are possible
(let-values ([(head tail) (split-at xs (car bps))])
(cons tail (loop head (cdr bps)))))))))
(define+provide+safe (shift xs how-far [fill-item #f] [cycle #f])
((list? integer?) (any/c boolean?) . ->* . list?)
(define abs-how-far (abs how-far))
(cond
[(> abs-how-far (length xs)) (error 'shift "index is too large for list\nindex: ~a\nlist: ~v" how-far xs)]
[(= how-far 0) xs]
[(positive? how-far)
(define filler (if cycle
(take-right xs abs-how-far)
(make-list abs-how-far fill-item)))
(append filler (drop-right xs abs-how-far))]
[else ; how-far is negative
(define filler (if cycle
(take xs abs-how-far)
(make-list abs-how-far fill-item)))
(append (drop xs abs-how-far) filler)]))
(define+provide+safe (shifts xs how-fars [fill-item #f] [cycle #f])
((list? integers?) (any/c boolean?) . ->* . (listof list?))
(map (λ(how-far) (shift xs how-far fill-item cycle)) how-fars))
;; todo: can this work in typed context? couldn't figure out how to polymorphically `apply values`
;; macro doesn't work either
(define+provide+safe (shift/values xs shift-amount-or-amounts [fill-item #f] [cycle #f])
((list? (or/c integers? integer?)) (any/c boolean?) . ->* . any)
(apply values ((if (list? shift-amount-or-amounts)
shifts
shift) xs shift-amount-or-amounts fill-item cycle)))