kcsongor

type family RowToList (r :: * -> *) :: [(Symbol, *)] where
  RowToList (l :*: r)
    = Merge (RowToList l) (RowToList r)
  RowToList (S1 ('MetaSel ('Just name) _ _ _) (Rec0 a))
    = '[ '(name, a)]
  RowToList (M1 _ m a)
    = RowToList a
  RowToList _
    = '[]

kcsongor

{-# LANGUAGE DataKinds              #-}
{-# LANGUAGE FlexibleContexts       #-}
{-# LANGUAGE FlexibleInstances      #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE KindSignatures         #-}
{-# LANGUAGE PolyKinds              #-}
{-# LANGUAGE TypeFamilies           #-}
{-# LANGUAGE TypeOperators          #-}
{-# LANGUAGE UndecidableInstances   #-}

kcsongor

{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}

module Overlapping where

class C a b where
  f :: a -> b -> Bool

instance C a b where
  f _ _ = False

kcsongor

{-# LANGUAGE DataKinds           #-}
{-# LANGUAGE GADTs               #-}
{-# LANGUAGE KindSignatures      #-}
{-# LANGUAGE Rank2Types          #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications    #-}

import Control.Lens

--------------------------------------------------------------------------------

kcsongor

{-# LANGUAGE DataKinds            #-}
{-# LANGUAGE PolyKinds            #-}
{-# LANGUAGE TypeFamilies         #-}
{-# LANGUAGE TypeOperators        #-}
{-# LANGUAGE UndecidableInstances #-}

-- (some examples at the bottom)

import Data.Kind (Constraint, Type)
import GHC.TypeLits (Nat, type (+), type (*))

kcsongor

{-# LANGUAGE AllowAmbiguousTypes  #-}
{-# LANGUAGE DataKinds            #-}
{-# LANGUAGE DeriveGeneric        #-}
{-# LANGUAGE ExplicitForAll       #-}
{-# LANGUAGE FlexibleContexts     #-}
{-# LANGUAGE FlexibleInstances    #-}
{-# LANGUAGE PolyKinds            #-}
{-# LANGUAGE TypeFamilies         #-}
{-# LANGUAGE TypeOperators        #-}
{-# LANGUAGE UndecidableInstances #-}

kcsongor

{-# LANGUAGE AllowAmbiguousTypes   #-}
{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE DeriveGeneric         #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE KindSignatures        #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PolyKinds             #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE TypeFamilies          #-}

kcsongor

object Main {

  /*
   * First thing first, we turn on a ("advanced") language feature via
   * `import scala.language.higherKinds`
   *
   * This is so that we can express higher-kinded types (HKTs) in generic
   * parameters.  Comes in handy for `Functor`, as all functors are HKTs, and
   * also for `Fix`, for similar reasons.
   *

kcsongor

{-# LANGUAGE DataKinds              #-}
{-# LANGUAGE FlexibleInstances      #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE GADTs                  #-}
{-# LANGUAGE KindSignatures         #-}
{-# LANGUAGE PolyKinds              #-}
{-# LANGUAGE TypeFamilies           #-}
{-# LANGUAGE TypeFamilyDependencies #-}
{-# LANGUAGE TypeOperators          #-}

kcsongor

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE StandaloneDeriving #-}