Singleton types

code:singleton.hs

data Question a = Q String (QType a)

deriving instance Show (Question a)

data QType :: * -> * where

QYesNo :: QType Bool

QQuant :: QType Int

deriving instance Show (QType a)

Singleton types provide a term-level representative for types.

Singleton types are quite a useful concept in type-level programming that we'll encounter frequently.

Useful links