Jon,
This is a crazy idea I've been working on: overload the syntax "x y" so it can mean function application "f x = f(x)" or multiplication "x y = x*y". The reason is simply that I appreciate the brevity of MLs function application but I also appreciate the brevity of Mathematica's multiplication.
Is it possible to implement this in Haskell using type classes? Is there any way this could actually be practicable?
Well, of course, it is certainly not possible to implement it directly. Juxtaposition denotes by no means an ordinary binary operator. If you do pick an ordinary binary operator for application, say (#), then you can get quite far with some language extensions, although I think it'll render your code less readable. Anyway, I remember doing this dark deed once when working with finite maps. I use associated type synonyms here, because we should get used to them anyway ;-). However, I'll attach a snippet employing functional dependencies, so you can actually play with it: infixl 9 # class Fun a where type Dom a :: * type Cod a :: * (#) :: a -> Dom a -> Cod a Now, let's have some fun ;-). instance Fun (a -> b) where type Arg (a -> b) = a type Res (a -> b) = b (#) = ($) instance Fun Int where type Arg Int = Int type Res Int = Int (#) = (*) instance Fun Bool where type Arg Bool = Bool type Res Bool = Bool (#) = (&&) instance (Eq a) => Fun [(a, b)] where type Arg [(a, b)] = a type Res [(a, b)] = Maybe b (#) = flip lookup And here we go: head # [2, 3, 5] ==> 2 2 # 3 ==> 6 False # True ==> False [('E', 2), ('H', 3), ('C', 5)] # 'E' ==> Just 2 Now, how practicable is it? As said, I think constructions like this have a negative impact on the readability of your programs. Moreover, overloading function applications is bound to introduce a lot of ambiguities in your programs and, hence, the need for type annotations. Cheers, Stefan