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