Curry

[opeltre]

Implement:

curry   :: ((a, b) -> c) -> a -> b -> c
uncurry :: (a -> b -> c) -> (a, b) -> c

As methods of the Arrow class.

Then, given arity of function f, return partial application (slice) of f with smaller number of arguments.

To do this properly, we should have product types, so that:

Arrow(A * B, C) ~ Arrow(A, Arrow(B, C))

And arity 2 is infered from the input type A * B.

[opeltre]

More generally implement the whole cartesian structure on types:

A | B  # union type
A * B  # product type
B ** A # exponentiation: Arrow(A, B)

[opeltre]

Cartesian structure merged in #10