|Version 1 (modified by diatchki, 4 years ago) (diff)|
There is a new kind, Nat. It is completely separate from GHC's hierarchy of sub-kinds, so Nat is only a sub-kind of itself.
The inhabitants of Nat are an infinite family of (empty) types, corresponding to the natural numbers:
0, 1, 2, ... :: Nat
These types are linked to the value world by a small library with the following API:
module GHC.TypeNats where data Nat (n :: Nat) -- Abstract "singleton" types. natToInteger :: Nat n -> Integer -- Convert a singleton to an integer. integerToNat :: Integer -> (forall n. Nat n -> a) -> a -- Convert an integer into a singleton. class TypeNat n where nat :: Nat n -- A value in a "singleton" type. instance TypeNat 0 instance TypeNat 1 instance TypeNat 2 ... -- property: natToInteger (nat :: Nat n) == n