70 lines
1.8 KiB
Racket
70 lines
1.8 KiB
Racket
#lang racket/base
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(require (for-syntax racket/base) racket/contract/base)
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;; Added by samth:
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(provide in-syntax in-pairs in-sequence-forever sequence-lift)
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(define-sequence-syntax in-syntax
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(lambda () #'(lambda (e) (in-list (syntax->list e))))
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(lambda (stx)
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(syntax-case stx ()
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[[ids (_ arg)]
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#'[ids (in-list (syntax->list arg))]])))
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(define (in-pairs seq)
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(make-do-sequence
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(lambda ()
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(let-values ([(more? gen) (sequence-generate seq)])
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(values (lambda (e) (let ([e (gen)]) (values (car e) (cdr e))))
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(lambda (_) #t)
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#t
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(lambda (_) (more?))
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(lambda _ #t)
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(lambda _ #t))))))
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(define (in-sequence-forever seq val)
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(make-do-sequence
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(lambda ()
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(let-values ([(more? gen) (sequence-generate seq)])
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(values (lambda (e) (let ([e (if (more?) (gen) val)]) e))
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(lambda (_) #t)
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#t
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(lambda (_) #t)
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(lambda _ #t)
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(lambda _ #t))))))
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(define (sequence-lift f seq)
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(make-do-sequence
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(lambda ()
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(let-values ([(more? gen) (sequence-generate seq)])
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(values (lambda (e) (f (gen)))
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(lambda (_) #t)
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#t
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(lambda (_) (more?))
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(lambda _ #t)
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(lambda _ #t))))))
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;; Added by stamourv (from David Vanderson (david.vanderson at gmail.com)):
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(provide/contract
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[in-slice (exact-positive-integer? any/c . -> . any)])
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(define (in-slice k seq)
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(unless (sequence? seq) (raise-type-error 'in-slice "sequence" seq))
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(make-do-sequence
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(lambda ()
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(define-values (more? get) (sequence-generate seq))
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(values
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(lambda (_)
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(for/list ((i k)
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#:when (more?))
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(get)))
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values
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#f
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#f
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(lambda (val) (0 . < . (length val)))
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#f))))
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