[racket] fingertree / nested datatype

Quick answer is to replace
(define-type (Fingertree a) (U Empty (Single a) (Deep a)))
With
(struct: (a) Fingertree ((v : (U Empty (Single a) (Deep a)))))

Still looking into understanding what is going on, but I believe you
will need to introduce a Rec somewhere to get it how you want.

On Wed, Apr 10, 2013 at 6:27 PM, Anthony Carrico <acarrico at memebeam.org> wrote:
> I've been reading about fingertrees, and I figure the best way to
> understand is to implement. This is my first experience with typed
> racket. Are nested datatypes supported?
>
> This is my first try:
>
> typed-fingertree.rkt:19:48: Type Checker: Structure type constructor
> Deep applied to non-regular arguments ((U (Node2 a) (Node3 a)))
>
> #lang typed/racket
>
> (struct: (a) Digit1 ((v0 : a)))
> (struct: (a) Digit2 ((v0 : a) (v1 : a)))
> (struct: (a) Digit3 ((v0 : a) (v1 : a) (v2 : a)))
> (struct: (a) Digit4 ((v0 : a) (v1 : a) (v2 : a) (v3 : a)))
> (define-type (Digit a) (U (Digit1 a) (Digit2 a) (Digit3 a) (Digit4 a)))
>
> (struct: (a) Node2 ((v0 : a) (v1 : a)))
> (struct: (a) Node3 ((v0 : a) (v1 : a) (v2 : a)))
> (define-type (Node a) (U (Node2 a) (Node3 a)))
>
> (struct: Empty ())
> (struct: (a) Single ((v : a)))
> (struct: (a) Deep ((left : (Digit a))
>                    (spine : (Fingertree (Node a)))
>                    (right : (Digit a))))
>
> (define-type (Fingertree a) (U Empty (Single a) (Deep a)))
>
> Thank you!
>
> --
> Anthony Carrico
>
>
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