I'm confused, Sam. Is the example with the indirect struct less problematic somehow? Or should it be failing?
Carl Eastlund -- WARNING! Poorly-typed cell phone email precedes. On Apr 11, 2013 7:23 AM, "Sam Tobin-Hochstadt" <sa...@ccs.neu.edu> wrote: > The reason this doesn't work is that non-regular datatypes require > significantly more algorithmic complexity to avoid non-termination/be > correct. In particular, I don't know of a subtyping algorithm for > non-regular datatypes. > > Sam > > On Thu, Apr 11, 2013 at 12:58 AM, Eric Dobson <eric.n.dob...@gmail.com> > wrote: > > So it looks like that you need an indirection struct, here is a simple > example. > > > > #lang typed/racket > > > > > > (struct: (a) Indirect ((v : (Deep a)))) > > (struct: (a) Deep ((spine : (Indirect (List a))))) > > ;(struct: (a) Deep ((spine : (Deep (List a))))) > > > > The uncommented version typechecks, but the commented one does not. I > > understand why this works in the implementation, but don't know the > > theoretical reason why the implementation prevents it, since Indirect > > and Deep should be isomorphic. > > > > On Wed, Apr 10, 2013 at 9:43 PM, Eric Dobson <eric.n.dob...@gmail.com> > wrote: > >> 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 <acarr...@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 > >>> > >>> > >>> ____________________ > >>> 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 > >
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