552d6de953
The generics library now generates a `name/c` macro for a generic interface `name`. The combinator can be used to contract instances (or constructors) of a generic interface across standard contract boundaries.
54 lines
1.5 KiB
Racket
54 lines
1.5 KiB
Racket
#lang racket/load
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(module a racket/base
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(require racket/generic)
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(define-generics simple-dict
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(dict-ref simple-dict key [default])
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(dict-set simple-dict key val)
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(dict-remove simple-dict key))
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(provide dict-ref
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dict-set
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dict-remove
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gen:simple-dict
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simple-dict?
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simple-dict/c))
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(module b racket/base
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(require 'a racket/contract)
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;; same as in "alist.rkt"
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(define-struct alist (v)
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#:methods gen:simple-dict
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[(define (dict-ref dict key
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[default (lambda () (error "key not found" key))])
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(cond [(assoc key (alist-v dict)) => cdr]
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[else (if (procedure? default) (default) default)]))
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(define (dict-set dict key val)
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(alist (cons (cons key val) (alist-v dict))))
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(define (dict-remove dict key)
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(define al (alist-v dict))
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(remove* (assoc key al) al))])
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(provide/contract
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[make-alist
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(-> list?
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(simple-dict/c
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[dict-ref (->* (simple-dict? symbol?) (any/c) integer?)]
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[dict-set (-> simple-dict? symbol? integer? simple-dict?)]
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[dict-remove (-> simple-dict? symbol? simple-dict?)]))]))
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(module c racket/base
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(require 'a 'b rackunit)
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(define dict (make-alist '((a . 5) (b . 10))))
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(check-equal? (dict-ref dict 'a) 5)
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(check-equal? (dict-ref dict 'b) 10)
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(check-exn exn:fail:contract?
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(λ () (dict-set dict 'a "bad")))
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(check-exn exn:fail:contract?
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(λ () (dict-set dict "bad" 5))))
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(require 'c)
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