How to get the value of a Maybe in Haskell

Question

I'm relatively new to Haskell and began to read "Real World Haskell".

I Just stumbled over the type Maybe and have a question about how to receive the actual value from a Just 1 for example.

I have written the following code:

combine a b c = (eliminate a, eliminate b, eliminate c)
                where eliminate (Just a) = a
                      eliminate Nothing = 0

This works fine if I use:

combine (Just 1) Nothing (Just 2)

But if I change, for example, 1 to a String it doesn't work.

I think I know why: because eliminate has to give back one type, which is, in this case, an Int. But how can I change eliminate to deal at least with Strings (or maybe with all kind of types)?