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47 lines
2.3 KiB
Racket
47 lines
2.3 KiB
Racket
#lang racket/base
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(require "define.rkt" "coerce.rkt" "len.rkt" racket/list racket/set racket/sequence racket/stream racket/dict)
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(define (sliceable-container? x)
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(ormap (λ(proc) (proc x)) (list list? string? symbol? vector? path? (λ(i) (and (not (dict? i)) (sequence? i))))))
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(define (gettable-container? x)
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(ormap (λ(proc) (proc x)) (list sliceable-container? dict?)))
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(define+provide+safe (get container start [end #f])
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((gettable-container? any/c) ((or/c (and/c integer? positive?) #f)) . ->* . any)
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(define result
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;; use handler to capture error & print localized error message
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(with-handlers ([exn:fail? (λ(exn) (error (format "get: couldn't retrieve ~a from ~a" (if end (format "items ~a through ~a" start end) (format "item ~a" start)) container)))])
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(let ([end (if (and (equal? end #f) (sliceable-container? container)) (add1 start) end)])
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(cond
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[(list? container) (for/list ([i (in-range start end)]) (list-ref container i))]
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[(vector? container) (for/vector ([i (in-range start end)]) (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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[(path? container) (get (explode-path container) start end)]
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[(dict? container) (dict-ref container start)]
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[(sequence? container) (get (->list container) start end)]
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[else (error)]))))
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;; don't return single-item results inside a list
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;; check for integer because integers don't have length
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(if (and (not (integer? result)) (= (len result) 1) (sliceable-container? container))
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(car (->list result))
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result))
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(define (listlike-container? container)
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(ormap (λ(pred) (pred container)) (list vector? set? sequence?)))
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(define+provide+safe (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)]
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[(dict? container) (dict-has-key? container item)]
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[(path? container) (in? (->path item) (explode-path container))]
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[(stringish? container) (regexp-match (->string item) (->string container))]
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;; location relevant because dicts and strings are also listlike (= sequences)
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[(listlike-container? container) (in? item (->list container))]
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[else #f])))
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