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Fix assoc to obey lens laws

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This commit is contained in:
JackFirth 2015-02-22 19:28:48 -08:00
parent cdec0a9b20
commit 888924b1f3
1 changed files with 17 additions and 10 deletions
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27
lenses/list.rkt
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@ -51,28 +51,35 @@
assoc-pair))
(map swap-assoc-pair assoc-list))
(define (assoc-set assoc-list key value #:is-equal? [equal? equal?])
(define (set-assoc-pair assoc-pair)
(if (equal? (first assoc-pair) key)
(list (first assoc-pair) value)
assoc-pair))
(map set-assoc-pair assoc-list))
(module+ test
(define assoc-list '((a 1) (b 2) (c 3)))
(check-equal? (assoc-swap assoc-list '(b 2) '(FOO BAR))
'((a 1) (FOO BAR) (c 3))))
(define ((assoc-lens assoc-key #:is-equal? [equal? equal?]) assoc-list)
(define assoc-pair (assoc assoc-key assoc-list equal?))
(define (assoc-set new-assoc-pair)
(define ((assoc-lens key #:is-equal? [equal? equal?]) assoc-list)
(define assoc-pair (assoc key assoc-list equal?))
(define (assoc-lens-set v)
(if assoc-pair
(assoc-swap assoc-list assoc-pair new-assoc-pair #:is-equal? equal?)
(append assoc-list (list new-assoc-pair))))
(values assoc-pair assoc-set))
(assoc-set assoc-list key v #:is-equal? equal?)
(append assoc-list (list (list key v)))))
(values assoc-pair assoc-lens-set))
(module+ test
(define assoc-a-lens (assoc-lens 'a))
(define assoc-d-lens (assoc-lens 'd))
(check-equal? (lens-view assoc-a-lens assoc-list) '(a 1))
(check-equal? (lens-set assoc-a-lens assoc-list '(FOO BAR))
'((FOO BAR) (b 2) (c 3)))
(check-equal? (lens-set assoc-a-lens assoc-list 100)
'((a 100) (b 2) (c 3)))
(check-false (lens-view assoc-d-lens assoc-list))
(check-equal? (lens-set assoc-d-lens assoc-list '(FOO BAR))
'((a 1) (b 2) (c 3) (FOO BAR))))
(check-equal? (lens-set assoc-d-lens assoc-list 4)
'((a 1) (b 2) (c 3) (d 4))))
(define (assv-lens assv-key)
(assoc-lens assv-key #:is-equal? eqv?))