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sugar/container.rkt

67 lines
2.7 KiB
Racket

#lang racket/base
(require racket/contract racket/vector racket/list)
(require "coerce.rkt" "len.rkt")
(provide get in?)
(define/contract (sliceable-container? x)
(any/c . -> . boolean?)
(ormap (λ(proc) (proc x)) (list list? string? symbol? vector?)))
(define/contract (gettable-container? x)
(any/c . -> . boolean?)
(ormap (λ(proc) (proc x)) (list sliceable-container? hash?)))
;; general way of fetching an item from a container
(define/contract (get container start [end #f])
((gettable-container? any/c) ((λ(i)(or (integer? i) (and (symbol? i) (equal? i 'end)))))
. ->* . any/c)
(set! end
(if (sliceable-container? container)
(cond
;; treat negative lengths as offset from end (Python style)
[(and (integer? end) (< end 0)) (+ (len container) end)]
;; 'end slices to the end
[(equal? end 'end) (len container)]
;; default to slice length of 1 (i.e, single-item retrieval)
[(equal? end #f) (add1 start)]
[else end])
end))
(define result (cond
;; for sliceable containers, make a slice
[(list? container) (for/list ([i (range start end)])
(list-ref container i))]
[(vector? container) (for/vector ([i (range start end)])
(vector-ref container i))]
[(string? container) (substring container start end)]
[(symbol? container) (->symbol (get (->string container) start end))]
;; for hash, just get item
[(hash? container) (hash-ref container start)]
[else #f]))
;; don't return single-item results inside a list
(if (and (sliceable-container? container) (= (len result) 1))
(car (->list result))
result))
;; general way of testing for membership (à la Python 'in')
;; put item as first arg so function can use infix notation
;; (item . in . container)
(define/contract (in? item container)
(any/c any/c . -> . coerce/boolean?)
(cond
[(list? container) (member item container)] ; returns #f or sublist beginning with item
[(vector? container) (vector-member item container)] ; returns #f or zero-based item index
[(hash? container)
(and (hash-has-key? container item) (get container item))] ; returns #f or hash value
[(string? container) (regexp-match (->string item) (->string container))] ; returns #f or substring beginning with item
[(symbol? container) ((->string item) . in? . (->string container))] ; returns #f or subsymbol (?!) beginning with item
[else #f]))