| I think (untested) that in this particular case you can get around the
| problem using scoped type variables:
|
| > g :: forall a. Num a => T a -> T a
| > g x = f x (42 :: a)
|
| In fact, this seems to be the general pattern for fixing problems like
| this with type families: add extra "witness
On Tue, Nov 3, 2009 at 3:20 PM, Max Bolingbroke
wrote:
> 2009/11/3 Daniel Fischer :
>> Am Dienstag 03 November 2009 19:28:55 schrieb Roland Zumkeller:
>>> Hi,
>>>
>>> Compiling
>>>
>>> > class WithT a where
>>> > type T a
>>> >
>>> > f :: T a -> a -> T a
>>> > f = undefined
>>> >
>>> > g x = f x
2009/11/3 Daniel Fischer :
> Am Dienstag 03 November 2009 19:28:55 schrieb Roland Zumkeller:
>> Hi,
>>
>> Compiling
>>
>> > class WithT a where
>> > type T a
>> >
>> > f :: T a -> a -> T a
>> > f = undefined
>> >
>> > g x = f x 42
>>
>> with -XTypeFamilies -fwarn-missing-signatures gives:
>>
>>
Am Dienstag 03 November 2009 19:28:55 schrieb Roland Zumkeller:
> Hi,
>
> Compiling
>
> > class WithT a where
> > type T a
> >
> > f :: T a -> a -> T a
> > f = undefined
> >
> > g x = f x 42
>
> with -XTypeFamilies -fwarn-missing-signatures gives:
>
> Inferred type: g :: forall a. (N
