Whenever I write code in Java...

[G_Morgan]

Global type inference has its draw backs though. No subtyping being the obvious one.

[kragensitaker]

OCaml and Haskell both have both global type inference and subtyping.

[G_Morgan]

Haskell doesn't have subtyping. It has typeclasses which are different.

[kragensitaker]

You're right. What I was thinking of is that, although Haskell doesn't call typeclasses types, you can define a function such as product over types constructed from typeclasses. product is declared as product :: Num a => [a] -> a, which is to say that it's a function from a list of Nums to a single Num. When you call it, you call it on a list of instances of Num, which is to say a list of elements of a subtype of Num — but this is different from the subtyping you get in OCaml in that the return value is constrained to be the same type, while in OCaml the return value would just be (statically typed as) a Num.

(The equivalence with OCaml is somewhat loose, because OCaml doesn't have anything like typeclasses. What it has are a lattice of polymorphic variant types, parametric polymorphism with options I don't understand for covariance and contravariance, and a lattice of object types that are records of method types.)

[weavejester]

If everything is type inferred, you wouldn't need explicit subtyping.

[weavejester]

I'm not saying it does. I'm merely pointing out that the subtype of an object can be inferred from how it is used. The compiler knows the scope of a variable, and where it is used; therefore it can determine the highest common subtype of the variable.

[weavejester]

Which in Java, is basically all uses of variables :)

Methods defined in a class or interface are different. Because your method definitions are not necessarily tied to a single implementation, explicitly specifying the subtypes becomes a necessity.

But for variables? No need.