Why not do this with the type, instead of making this polymorphic? Sam
On Fri, Sep 26, 2014 at 7:35 PM, Alexander D. Knauth <alexan...@knauth.org> wrote: > 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 > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > > ____________________ Racket Users list: http://lists.racket-lang.org/users
