{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeFamilies #-}

module Options.Harg.Sources.NoSource
  ( NoSource,
    noSources,
  )
where

import qualified Barbies as B
import Data.Kind (Type)
import GHC.Generics (Generic)
import Options.Harg.Sources.Types

-- | Throwaway type whose 'GetSource' instance returns no value.
data NoSource (f :: Type -> Type) = NoSource
  deriving (Generic, B.FunctorB, B.TraversableB, B.ApplicativeB)

instance GetSource NoSource f where
  type SourceVal NoSource = ()
  getSource _ctx _ = pure ()

-- | Shorthand for writing 'NoSource'.
noSources :: NoSource f
noSources = NoSource