[Haskell-cafe] Type error depending on scope of pattern matching

[htebalaka]

Alright. The first two examples show the issue and a fix for it; the last two
have the same issue but existential quantification prevents the fix.

grad has type "(Num a, Traversable t) => (forall s. Reifies s Tape => t
(Reverse s a) -> Reverse s a) -> t a -> t a", and I'm basically trying to
supply a function to it, either by being polymorphic over all Num (of which
Reverse s a is an instance), or by providing the specific 'Reifies s Tape =>
...' type, neither of which are working.




amindfv wrote
> You'll probably get more responses if you paste the code inline.
> 
> tom
> 
> El Aug 1, 2015, a las 11:25, htebalaka <

> goodingm@

> > escribió:
> 
>> I'm curious if anyone can tell me why moving the pattern matching in
>> these
>> two examples makes it fail to compile, and what can be done to resolve
>> the
>> same issue in either of the latter two examples. As far as I can tell
>> these
>> should be equivalent. Unfortunately the solution used in the first
>> examples
>> won't work in the later ones due to the existential quantification. I've
>> been asking on #haskell for a few days but haven't been able to find
>> anyone
>> who knows what the issue is.
>> 
>> Code is available here:  http://lpaste.net/137586
>> <http://lpaste.net/137586>  
>> 
>> 
>> 
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