[racket] Typed Racket generalization and inference for containers

This is already fixed at HEAD,
https://github.com/plt/racket/commit/1334e8dcc77854ac826306d3f6a36150cb0bf0c1
has the fix.

On Sun, Apr 7, 2013 at 7:47 AM, Sam Tobin-Hochstadt <samth at ccs.neu.edu> wrote:
> On Sun, Apr 7, 2013 at 10:18 AM, Andrey Larionov <anlarionov at gmail.com> wrote:
>> Hello, Racket community.
>> I'm a newbie and just started study Racket and Typed Racket and a little
>> confused with generalization and inference.
>> I found what inference works different for different containers type. For
>> example:
>> Set:
>>> (set 0 195 196)
>> - : (Setof Byte)
>> (set 0 195 196)
>> List:
>>> '((195 . 1) (196 . 2))
>> - : (Listof (Pairof Positive-Byte Positive-Byte)) [generalized from (List
>> (Pairof Positive-Byte One) (Pairof Positive-Byte Positive-Byte))]
>> '((195 . 1) (196 . 2))
>> HashTable:
>>> #hash((195 . 1) (196 . 2) (197 . 3))
>> - : (HashTable Integer Integer)
>> '#hash((195 . 1) (197 . 3) (196 . 2))
>
> This is because sets and lists are immutable, while hash tables are
> (potentially) mutable.  Typed Racket generates more general types for
> mutable data because otherwise the lack of subtyping would make such
> data very hard to use.
>
> In fact, this hash table is immutable, but Typed Racket doesn't
> distinguish between mutable and immutable hash tables.  If it did,
> then you'd get the result you'd expect here.
>
>> Actually i'm writing library for msgpack protocol and decide to implement it
>> in Typed Racket. Here is my code which did't type check and broke all other
>> program:
>> (define-type Atom (U False True Null))
>> (: atoms (HashTable Byte Atom))
>> (define atoms #hash((#xc0 . ())
>>                     (#xc3 . #t)
>>                     (#xc2 . #f)))
>> Error: Type Checker: Expected (HashTable Byte Atom), but got (HashTable
>> Integer Atom) in: #hash((195 . #t) (194 . #f) (192 . ()))
>
> This is a bug. You may be able to work around it by using the `hash`
> function, instead of the literal data constructor.
>
> Sam
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