Add iterators as tests for generics.

Equivalent to streams, so not useful to provide.
This commit is contained in:
Vincent St-Amour 2012-05-21 11:58:08 -04:00
parent ec2563fdd3
commit 08cd358300
3 changed files with 89 additions and 2 deletions

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@ -0,0 +1,69 @@
#lang racket/base
(require racket/private/generics racket/sequence)
;; This was designed as a higher-level interface on top of sequences,
;; but it turns out streams can do all that already (including state),
;; making iterators redundant. Kept around as extra tests.
(define-values (prop:iterator iterator? iterator-accessor)
(make-struct-type-property
'iterator
#f
;; Iterators are automatically sequences, but don't have the full
;; flexibility of sequences: they are their own initial state, and
;; they can only look at their state to decide if iteration is over.
;; Given that extra field can be added to the iterator, there is no
;; loss of expressiveness.
(list (cons prop:sequence
(lambda (method-table) ; 3-vector
(define iterator-first (vector-ref method-table 0))
(define iterator-rest (vector-ref method-table 1))
(define iterator-continue? (vector-ref method-table 2))
(lambda (t)
(make-do-sequence
(lambda ()
(values iterator-first
iterator-rest ; needs to create a new struct
t
iterator-continue?
(lambda (v) #t)
(lambda (t v) #t))))))))))
(define-generics (iterator prop:iterator iterator?
#:defined-table dummy
#:coerce-method-table #f
#:prop-defined-already? iterator-accessor)
(iterator-first iterator)
(iterator-rest iterator)
(iterator-continue? iterator))
(struct list-iterator (l)
#:property prop:iterator
(methods iterator
(define (iterator-first x) (car (list-iterator-l x)))
(define (iterator-rest x) (list-iterator (cdr (list-iterator-l x))))
(define (iterator-continue? x) (not (null? (list-iterator-l x))))))
(struct vector-iterator (i v)
#:property prop:iterator
(methods iterator
(define (iterator-first x) (vector-ref (vector-iterator-v x)
(vector-iterator-i x)))
(define (iterator-rest x) (vector-iterator (add1 (vector-iterator-i x))
(vector-iterator-v x)))
(define (iterator-continue? x) (not (>= (vector-iterator-i x)
(vector-length
(vector-iterator-v x)))))))
(module+ test
(require rackunit)
(define s1 (list-iterator '(#t #t #f)))
(check-true (sequence-ormap values s1))
(check-false (sequence-andmap values s1))
(define s2 (vector-iterator 0 '#(1 2 3)))
(check-equal? (sequence-fold + 0 s2) 6)
)

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@ -12,6 +12,18 @@
(define (stream-rest generic-stream)
(rest (list-stream-v generic-stream)))))
(struct vector-stream (i v)
#:property prop:stream
(methods generic-stream
(define (stream-first x) (vector-ref (vector-stream-v x)
(vector-stream-i x)))
(define (stream-rest x) (vector-stream (add1 (vector-stream-i x))
(vector-stream-v x)))
(define (stream-empty? x) (>= (vector-stream-i x)
(vector-length
(vector-stream-v x))))))
(module+ test
(require rackunit)
@ -29,4 +41,9 @@
(define l3 (stream-rest l2))
(check-true (stream? l3))
(check-true (stream-empty? l3)))
(check-true (stream-empty? l3))
(define s2 (vector-stream 0 '#(1 2 3)))
(check-equal? (sequence-fold + 0 s2) 6)
)

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@ -4,4 +4,5 @@
(submod "alist.rkt" test)
(submod "from-docs.rkt" test)
(submod "coercion.rkt" test)
(submod "stream.rkt" test))
(submod "stream.rkt" test)
(submod "iterator.rkt" test))