62 lines
1.7 KiB
Scheme
62 lines
1.7 KiB
Scheme
;; --- the customer manager ----------------------------------------------------
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#lang scheme
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(require "1.ss")
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;; implementation
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;; [listof (list basic-customer? secret-info)]
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(define all '())
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(define (find c)
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(define (has-c-as-key p) (id-equal? (basic-customer-id (car p)) c))
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(define x (filter has-c-as-key all))
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(if (pair? x) (car x) x))
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(define (active? c)
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(define f (find c))
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(pair? (find c)))
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(define not-active? (compose not active? basic-customer-id))
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(define count 0)
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(define (add c)
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(set! all (cons (list c 'secret) all))
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(set! count (+ count 1)))
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(define (name id)
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(define bc-with-id (find id))
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(basic-customer-name (car bc-with-id)))
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(define (set-name id name)
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(define bc-with-id (find id))
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(set-basic-customer-name! (car bc-with-id) name))
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(define c0 0)
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;; end of implementation
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;; interface
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(provide/contract
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;; how many customers are in the db?
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[count natural-number/c]
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;; is the customer with this id active?
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[active? (-> id? boolean?)]
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;; what is the name of the customer with this id?
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[name (-> (and/c id? active?) string?)]
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;; change the name of the customer with this id
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[set-name (->d ([id id?] [nn string?])
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()
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[result any/c] ;; result contract
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#:post-cond
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(string=? (name id) nn))]
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[add (->d ([bc (and/c basic-customer? not-active?)])
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()
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;; A pre-post condition contract must use a side-effect
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;; to express this contract via post-conditions
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#:pre-cond (set! c0 count) ;; pre
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[result any/c] ;; result contract
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#:post-cond (> count c0))])
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;; end of interface
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