Algebraic Data Types

[HuwCampbell]

Currently we support a few special case ADTs. It would be nice to declare them in the Prelude and allow others to add their own. Just like in Haskell, we would need to wire some back in for things like box and reification.

Fortunately though, we because we don't offer recursion, we can restrict our types to simple products and sums.

From http://dev.stephendiehl.com/fun/009_datatypes.html

data Unit = Unit                 -- 1
data Empty                       -- 0
data (a * b) = Product a b       -- a * b
data (a + b) = Inl a | Inr b     -- a + b
-- We don't need these in Icicle
-- data Exp a b = Exp (a -> b)      -- a^b
-- data Rec f   = Rec (f (Rec f))   -- \mu

should do it.