module Control.Plus

( class Plus

, empty

, module Control.Alt

, module Data.Functor

) where

import Control.Alt (class Alt, alt, (<|>))

import Data.Functor (class Functor, map, void, ($>), (<#>), (<$), (<$>))

-- | The `Plus` type class extends the `Alt` type class with a value that

-- | should be the left and right identity for `(<|>)`.

-- |

-- | It is similar to `Monoid`, except that it applies to types of

-- | kind `* -> *`, like `Array` or `List`, rather than concrete types like

-- | `String` or `Number`.

-- |

-- | `Plus` instances should satisfy the following laws:

-- |

-- | - Left identity: `empty <|> x == x`

-- | - Right identity: `x <|> empty == x`

-- | - Annihilation: `f <$> empty == empty`

class Alt f <= Plus f where

empty :: forall a. f a

instance plusArray :: Plus Array where

empty = []