[Haskell-cafe] Aren't type system extensions fun? [Further analysis]

[Isaac Dupree]

>>>>    foo :: (Char -> a /\ Bool -> b) -> (a,b)
>>>
>>> a.k.a. find some value that matches both Char->a and Bool->b for some a and b.  Could use type-classes to do it. 

>> Uhmm... you mean something like (neglecting TC-related issues here)
>>
>> class C a b where
>>    fromChar :: Char -> a
>>    fromBool :: Bool -> b
> 
> Oops: i meant something like
> 
> class C x a b | x -> a,b where
>    fromChar :: x -> Char -> a
>    fromBool :: x -> Bool -> b

no... let me figure out what I meant.  Just somehow to have a single 
function that takes an argument of two different types without 
completely ignoring it.

class Arg a where
   whatYouPass :: a -> Something
instance Arg Char where
   whatYouPass = ...
instance Arg Bool where
   whatYouPass = ...

Then (foo whatYouPass) :: (Something, Something).
Or if it was
class Arg a where
   whatYouPass :: a -> a
then (foo whatYouPass) :: (Char, Bool).
And I'm sure there are ways to make the return type different if you 
want to think about FDs etc.

> 
> 
> Zun.
>