[racket] define-type on List and Listof

As Sam keeps saying, one day we will have kinds of higher meta-kind (as in Omega -> Omega) and then we can signal errors at the type level properly -- Matthias



On Jun 17, 2014, at 10:51 PM, Jon Zeppieri wrote:

> Well, I think that's because MyList had a different kind than List. List is a type constructor but not a type. MyList, on the other hand, is a (polymorphic) type, and it can't be applied; rather, its type variables need to be instantiated. Though, given its definition, I don't see how you could instantiate all of them.
> 
>> On Jun 17, 2014, at 8:48 PM, "Alexander D. Knauth" <alexander at knauth.org> wrote:
>> 
>> Could you represent it with something like (All (a …) (List a … a))?  
>> 
>> From reading the documentation it seems like it should work, but
>> When I tried it, I got this:
>> 
>> #lang typed/racket
>> 
>> (define-type MyList (All (a ...) (List a ... a)))
>> 
>> (ann '(1 2 3) (MyList 1 2 3))
>> 
>> . Type Checker: Type MyList cannot be applied, arguments were: (One 2 3) in: (MyList 1 2 3)
>> 
>>> On Jun 17, 2014, at 8:33 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
>>> 
>>> I imagine it's because there are no variable-arity type constructors in TR, and (List A ...) is fancy syntax for (Pairof A (Pairof ...  '()) ...) if that notation makes any sense.
>>> -Ian
>>> ----- Original Message -----
>>> From: "Spencer Florence" <spencer at florence.io>
>>> To: "racket" <users at racket-lang.org>
>>> Sent: Tuesday, June 17, 2014 5:32:55 PM GMT -05:00 US/Canada Eastern
>>> Subject: [racket] define-type on List and Listof
>>> 
>>> 
>>> 
>>> Hi all, 
>>> 
>>> I'm trying to rename some types in typed/racket but something odd is happening: 
>>> 
>>> 
>>> (define-type A Listof) 
>>> 
>>> works but: 
>>> 
>>> 
>>> (define-type B List) 
>>> 
>>> errors with "Type Checker: parse error in type; type name `List' is unbound in: List" 
>>> 
>>> Is this a bug or am I missing something? 
>>> 
>>> --Spencer 
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