You can think of structural record types as being formed by applying a special type constructor to a type-level collection of types: row Fields = [name: St

You can think of structural record types as being formed by applying a special type constructor to a type-level collection of types: row Fields = [name: String, age: Int] type Person = MkRecord Fields Which have kinds: MkRecord :: Row Type -> Type Fields :: Row Type Person :: Type You can construct variant types in a similar way: row Cases = [success: SyntaxTree, failure: ParseError] type ParseResult = MkVariant Cases Which have kinds: MkVariant :: Row Type -> Type Cases :: Row Type ParseResult :: Type Rows may contain things other than proper types, for example: row Effects = [foo: State s, bar: Except e] type Action = MkFunction Effects Which have kind: -- function types now take three arguments: -- - row of effects -- - argument type -- - return type MkFunction :: Row Effect -> Type -> Type -> Type Effects :: Row Effect Action :: Type -> Type -> Type