Hello all,
For school purposes, I would like to define something like this:
module SetOverList(
SetFromList
, SetOL(..)
) where
type SetFromList a = [a]
addEq :: Eq a => a -> SetFromList a -> SetFromList a
addEq v [] = [v]
addEq v l@(x:xs) = if x==v then l else x : addEq v xs
addOrd :: Ord a => a -> SetFromList a -> SetFromList a
addOrd v [] = [v]
addOrd v l@(x:xs) =
case compare x v of
GT -> v : l
EQ -> l
LT -> x : addOrd v xs
class SetOL a where
addElem :: a -> SetFromList a -> SetFromList a
instance (Eq a) => SetOL a where
addElem = addEq
instance (Ord a) => SetOL a where
addElem = addOrd
which does not work, of course (Flexible or Undecidable instances won't
help). The aim is to have addElem function that works differently
according to situation whether a type, which is base of the list/set, is
a member of class Eq or Ord. Could you point me or hint me how to get as
close as possible to the required solution? Maybe I'm not able to see an
obvious way...
Thanks,
Dušan
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