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Improve the implementation of in-slice.

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Vincent St-Amour 2015-08-07 14:47:43 -05:00
parent 2d23ca1414
commit 1a7b71fb20
1 changed files with 3 additions and 7 deletions
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10
racket/collects/unstable/sequence.rkt
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@ -62,22 +62,18 @@
;; Added by stamourv (from David Vanderson (david.vanderson at gmail.com)): ;; Added by stamourv (from David Vanderson (david.vanderson at gmail.com)):
(provide/contract (provide/contract
[in-slice (exact-positive-integer? any/c . -> . any)]) [in-slice (exact-positive-integer? sequence? . -> . any)])
(define (in-slice k seq) (define (in-slice k seq)
;; ELI: what's the point of using `any/c' above and then checking it here?
(unless (sequence? seq) (raise-type-error 'in-slice "sequence" seq))
(make-do-sequence (make-do-sequence
(λ () (λ ()
(define-values (more? get) (sequence-generate seq)) (define-values (more? get) (sequence-generate seq))
(values (values
(λ (_) (λ (_)
;; ELI: Add an `in-range' (for/list ([i (in-range k)] #:when (more?))
(for/list ([i k] #:when (more?))
(get))) (get)))
values values
#f #f
#f #f
;; ELI: Use `pair?' (λ (val) (pair? val))
(λ (val) (0 . < . (length val)))
#f)))) #f))))