Hi Ducis,
Is it possible to make combine the following "f" and "g" into one function?
"combine" is vague. You perhaps mean: look at the types of the arguments, and choose one function or the other?
Looks like it would require some typeclasses,
I'll answer the question as put (yes it needs typeclasses), but I can't help feel there's a backstory, and you might well be doing something that could be done better, if I knew what you're trying to achieve. Let's take the second one first
"eq1" and "eq2" into one function? eq1 :: (Eq a)=>a->a->Bool eq1 = (==) eq2 :: (Eq a,Eq b)=>a->b->Bool eq2 _ _ = False
f:: a -> b -> b f x y = y g:: a -> a -> a g x y = x So you want same argument types to drive which argument to pick? Or you want the return type to drive which argument? That's possible: look at the definition of class `Read` in the Prelude. Again we can
class Eqbytype a b where eqt :: a -> b -> Bool instance {-# OVERLAPPING #-} (Eq a) => Eqbytype a a where eqt = (==) instance {-# OVERLAPPABLE #-} Eqbytype a b where eqt _ _ = False Look at the Users Guide for what the OVERLAPPING/OVERLAPPABLE pragmas are doing. Note for the first instance I repeated type var `a` in the head, meaning: pick this instance if the two arguments to the method are of the same type. Note for the second instance, I didn't bother with the `Eq` constraint, since we can't compare values of distinct types. pick instances depending on a repeated type. But your requirements are not clear.
but at least in the first case [which I've put second], "a" and "b" should be any types.
No they can't: as you state it, you require either all three the same, or the second to be the same as the return type. Come back and ask a more focussed question once you've worked through the above. (And explain why you're asking.) The above code is untested, BTW. AntC