[racket] weird typed racket error

This version with `for/fold` works for me:

(for/fold : (U Index #f) ([k : (U Index #f) #f])
  ([i : Index (ann (in-range 5) (Sequenceof Index))])
  i)

Sam

On Sun, Jul 13, 2014 at 11:15 PM, Alexander D. Knauth
<alexander at knauth.org> wrote:
>
> On Jul 13, 2014, at 8:23 PM, Sam Tobin-Hochstadt <samth at cs.indiana.edu> wrote:
>
>> Probably, what's going on here is that `for/last` has a hidden loop
>> variable that starts off as `#f` and Typed Racket infers that to have
>> type `False`.
>
> I thought that was the whole point of adding the : (U Index #f), right?  To provide a type for that loop variable?
>
>>
>> If that's the case, there's nothing you can really do other than
>> rewrite this as `for/fold`.
>
> Well, I tried to use for/fold, but it kept telling me to add more type annotations even when I had annotated every
> little thing that I could.
> Then I tried reversing the sequences and using for/first (which would work for what I’m doing but not in general),
> but if I remember correctly that seemed to have the same problem.
> Then I tried using the reversed sequences with for/or instead of for/first and that worked fine.
> But If there’s a hidden loop variable starting of as `#f`, then for/or should have the same problem, but for/or works fine.
>
>>
>> Sam
>>
>> On Sun, Jul 13, 2014 at 7:57 PM, Alexander D. Knauth
>> <alexander at knauth.org> wrote:
>>> For some reason this:
>>> (for/last : (U Index #f)
>>>    ([i : Index (ann (in-range 5) (Sequenceof Index))])
>>>    i)
>>> Is giving me this error:
>>> . Type Checker: type mismatch
>>>  expected: False
>>>  given: Index in: (for/last : (U Index #f) ((i : Index (ann (in-range 5) (Sequenceof Index)))) i)
>>>
>>> Why is it expecting False?
>>> And is there some type annotation I can put somewhere to fix it or anything?
>>>
>>>
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>