Is it possible to have a struct that does certain things according to the guard?
#lang typed/racket
(struct (a) foo ([a : a]) #:transparent
#:guard (lambda (a _)
(unless (exact-integer? a)
(error 'foo "expected Integer, given ~v" a))
a))
(ann (foo (ann 1 Any)) (foo Integer))
(: x : (foo Any))
(define x (foo 1))
(ann (foo-a x) Integer)
;. Type Checker: Polymorphic function `foo1' could not be applied to arguments:
;Argument 1:
; Expected: a
; Given: Any
;
;Result type: (foo a)
;Expected result: (foo Integer)
; in: (foo (ann 1 Any))
;. Type Checker: Polymorphic function `foo-a' could not be applied to arguments:
;Argument 1:
; Expected: (foo a)
; Given: (foo Any)
;
;Result type: (a : ....)
;Expected result: Integer
; in: (foo-a x)
On Sep 25, 2014, at 9:42 PM, Alexander D. Knauth <alexan...@knauth.org> wrote:
> What I’m trying to accomplish is something more like this:
> #lang typed/racket
>
> (require "dimensions.rkt")
>
> (struct (d) unit ([name : Any] [scalar : Positive-Real] [dimension : d])
> #:transparent
> #:guard (lambda (name scalar dimension _)
> (unless (dimension? dimension)
> (error 'unit "expected Dimension, given ~v" dimension))
> (values name scalar dimension)))
>
> (define-type (Unitof d) (unit d))
>
> (define-type Unit (Unitof Dimension))
>
> (define Unit? (make-predicate Unit))
>
> (define-type Unitish
> (U (Unitof Any)
> Dimension
> Positive-Real))
>
> (: ->unit : (All (d) (case-> [(Unitof d) -> (Unitof d)]
> [Unitish -> Unit])))
> (define (->unit u)
> (cond [(unit? u)
> (unless (Unit? u) ; this should never happen anyway because of the
> guard
> (error '->unit "expected (Unitof Dimension), given ~v" u))
> u]
> [(dimension? u) (unit u 1 u)]
> [(positive-real? u) (unit u u dimensionless-dimension)]))
>
>
> On Sep 25, 2014, at 6:19 PM, Sam Tobin-Hochstadt <sa...@cs.indiana.edu> wrote:
>
>> No, I don't think you can do this. Can you say more about what you're
>> trying to accomplish?
>>
>> Sam
>>
>> On Thu, Sep 25, 2014 at 6:15 PM, Alexander D. Knauth
>> <alexan...@knauth.org> wrote:
>>> Do any of you have any advice for getting a function like this to
>>> type-check?
>>> #lang typed/racket
>>>
>>> (: check-int : (All (a) (case-> [a -> a]
>>> [Any -> Integer])))
>>> (define (check-int int)
>>> (unless (exact-integer? int)
>>> (error 'check-int "expected Integer, given ~v" int))
>>> int)
>>>
>>> ;. Type Checker: type mismatch
>>> ; expected: a
>>> ; given: Integer in: int
>>>
>>>
>>>
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