Has.hs

{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE NoImplicitPrelude     #-}

{-|
Module      : Headroom.Data.Has
Description : Simplified variant of @Data.Has@
Copyright   : (c) 2019-2020 Vaclav Svejcar
License     : BSD-3-Clause
Maintainer  : vaclav.svejcar@gmail.com
Stability   : experimental
Portability : POSIX

This module provides 'Has' /type class/, adapted to the needs of this
application.
-}

module Headroom.Data.Has
  ( Has(..)
  )
where

import           RIO

-- | Implementation of the /Has type class/ pattern.
class Has a t where
  {-# MINIMAL getter, modifier | hasLens #-}
  getter :: t -> a
  getter = getConst . hasLens Const

  modifier :: (a -> a) -> t -> t
  modifier f t = runIdentity (hasLens (Identity . f) t)

  hasLens :: Lens' t a
  hasLens afa t = (\a -> modifier (const a) t) <$> afa (getter t)

  viewL :: MonadReader t m => m a
  viewL = view hasLens