Who could please, explain a bit existential types?
It is required to organise a table with the key
data K = K1 | K2 | K3 {- ... -} deriving(Eq,Ord,Enum)
to put/extract there the items of different types, say, 'a' and
('a','b') as well. Is this possible?
Understanding nothing in this subject, i tried
data KTab = forall a. KT (FiniteMap K a)
f :: KTab -> KTab
f (KT t) = case addToFM t K1 'a' of
t' -> KT (addToFM t' K2 ('a','b'))
And this does not compile. Then, try
class Tab t k where lkp :: t a -> k -> Maybe a
addT :: t a -> k -> a -> t a
instance Tab KTab K where lkp (KT t) k = lookupFM t k
...
Also rejected. How to handle with this?
Thank you in advance.
------------------
Sergey Mechveliani
[EMAIL PROTECTED]
