2d4f3e2ac9
The layer is now redundant, since everything left in "pkgs" is in the "racket-pkgs" category.
57 lines
2.1 KiB
Racket
57 lines
2.1 KiB
Racket
#lang racket/base
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(require racket/generic
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racket/sequence
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(for-syntax racket/base))
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;; This was designed as a higher-level interface on top of sequences,
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;; but it turns out streams can do all that already (including state),
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;; making iterators redundant. Kept around as extra tests.
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(define-generics iterator
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(iterator-first iterator)
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(iterator-rest iterator)
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(iterator-continue? iterator)
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;; Iterators are automatically sequences, but don't have the full
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;; flexibility of sequences: they are their own initial state, and
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;; they can only look at their state to decide if iteration is over.
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;; Given that extra field can be added to the iterator, there is no
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;; loss of expressiveness.
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#:derive-property prop:sequence
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(lambda (t)
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(make-do-sequence
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(lambda ()
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(values iterator-first
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iterator-rest ; needs to create a new struct
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t
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iterator-continue?
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(lambda (v) #t)
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(lambda (t v) #t))))))
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(struct list-iterator (l)
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#:methods gen:iterator
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[(define (iterator-first x) (car (list-iterator-l x)))
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(define (iterator-rest x) (list-iterator (cdr (list-iterator-l x))))
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(define (iterator-continue? x) (not (null? (list-iterator-l x))))])
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(struct vector-iterator (i v)
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#:methods gen:iterator
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[(define (iterator-first x) (vector-ref (vector-iterator-v x)
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(vector-iterator-i x)))
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(define (iterator-rest x) (vector-iterator (add1 (vector-iterator-i x))
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(vector-iterator-v x)))
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(define (iterator-continue? x) (not (>= (vector-iterator-i x)
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(vector-length
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(vector-iterator-v x)))))])
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(module+ test
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(require rackunit)
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(define s1 (list-iterator '(#t #t #f)))
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(check-true (sequence-ormap values s1))
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(check-false (sequence-andmap values s1))
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(define s2 (vector-iterator 0 '#(1 2 3)))
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(check-equal? (sequence-fold + 0 s2) 6)
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)
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