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struct-type-property/ c
Version: 5.1
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42 Contracts for struct type properties

Ryan Culpepper <ryanc@racket-lang.org>

 (require unstable/prop-contract)

This library is unstable; compatibility will not be maintained. See Unstable for more information.

(struct-type-property/c value-contract) → contract?
  value-contract : contract?
Produces a contract for struct type properties. When the contract is applied to a struct type property, it produces a wrapped struct type property. When the wrapped struct type property is used to create a new struct type (via struct, make-struct-type, etc), it applies value-contract to the value associated with the property.

The contract has no effect on the struct type property accessor.

Examples:

  > (define-values (prop prop? prop-ref)
      (make-struct-type-property 'prop))
  > (define/contract wrapped
        (struct-type-property/c (-> any/c (-> number? number?)))
      prop)
  > (struct s (f)
      #:property wrapped (lambda (s) (s-f s)))
  > (define (get-f s) ((prop-ref s) s))
  > (define s1 (s add1))
  > ((get-f s1) 5)

  6

  > ((get-f s1) 'apple)

  self-contract violation: expected <number?>, given: 'apple

    contract on wrapped from (definition wrapped), blaming

  (definition wrapped)

    contract:

      (struct-type-property/c

       (-> any/c (-> number? number?)))

    at: eval:3.0

  > (define s2 (s (lambda (n) (if (zero? n) 'zero 'nonzero))))
  > ((get-f s2) 5)

  contract violation: expected <number?>, given: 'nonzero

    contract on wrapped from (definition wrapped), blaming

  top-level

    contract:

      (struct-type-property/c

       (-> any/c (-> number? number?)))

    at: eval:3.0

  > ((get-f s2) 'apple)

  self-contract violation: expected <number?>, given: 'apple

    contract on wrapped from (definition wrapped), blaming

  (definition wrapped)

    contract:

      (struct-type-property/c

       (-> any/c (-> number? number?)))

    at: eval:3.0

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