[Haskell-beginners] typeclass error

I have the following code -- foo.hs module Foo where class Foo a where bar :: a -> a instance Foo Int where bar i = i + 10 ------------------ It fails to compile withe following error *Foo> bar 10 <interactive>:1:4: Ambiguous type variable `t' in the constraints: `Num t' arising from the literal `10' at <interactive>:1:4-5 `Foo t' arising from a use of `bar' at <interactive>:1:0-5 Probable fix: add a type signature that fixes these type variable(s) *Foo> - Thanks Amitava Shee