Version 2 (modified by diatchki, 7 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

Basic Operations

data Nat n

class TypeNat n where
  nat :: Nat n

natToInteger :: Nat n -> Integer

checkNat :: TypeNat n => (Integer -> Bool) -> Maybe (Nat n)

Type-Level Operations

type family m ^ n :: Nat
type family m * n :: Nat
type family m + n :: Nat
class m <= n

Natural Numbers

data Natural = forall n . Natural !(Nat n)

data NaturalInteger
  = Negative Natural
  | NonNegative Natural

toNaturalInteger :: Integer -> NaturalInteger

subNatural :: Natural -> Natural -> NaturalInteger