Sign-indexed Peano numbers
1234567891011121314
{-# LANGUAGE DataKinds, GADTs, KindSignatures #-}
data Sign = Zero | Pos
data Nat :: Sign -> * where
Z :: Nat Zero
S :: Nat a -> Nat Pos
divide :: Nat a -> Nat Pos -> Nat a
divide = error "exercise for the reader"
main :: IO ()
main = return ()
Haskell
INFO