Hi Yotam,

One way to do this is to take an `Either Foo Bar` as an argument instead, then you can pattern match on its Left and Right. This is preferable if the function is only meant to work for a limited number of types. If you want it to be extensible to any number of types you can write a typeclass that contains `func` with the same type signature as you have now. There are also some extensions built in to GHC to do this automatically for you, but I don't recall exactly which ones to enable...

HTH,

Adam

On Tue, 10 Oct 2017 at 18:58 Yotam Ohad <yotam2206@gmail.com> wrote:

Hello cafe,
I am trying to do the following:

data Foo = Foo { a1 :: Int -> Int, a2 :: Int -> Char }
data Bar = Bar { a1 :: Int -> Int }

func :: a -> Maybe (Int -> Int) -- a is either Foo or Bar
func (x::(Bar/Foo) = Just $ a1 x
func _ = Nothing

I'm not sure how to implement this. All I know that the types are matching so I think it could be possible.

Thanks for your help
-Yotam
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