{- Copyright 2011-2018 Mario Blazevic This file is part of the Streaming Component Combinators (SCC) project. The SCC project is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. SCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with SCC. If not, see <http://www.gnu.org/licenses/>. -} -- | This module defines the 'MonoidApplicative' and 'MonoidAlternative' type classes. Their methods are specialized -- forms of the standard 'Applicative' and 'Alternative' class methods. Instances of these classes should override the -- default method implementations with more efficient ones. module Control.Applicative.Monoid ( MonoidApplicative(..), MonoidAlternative(..) ) where import Control.Applicative (Applicative (pure, (<*>)), Alternative ((<|>), some, many), (<$>)) import Data.Monoid (Monoid, mempty, mappend, mconcat) import Data.Semigroup (Semigroup, (<>)) class Applicative f => MonoidApplicative f where -- | A variant of the Applicative's '<*>' operator specialized for endomorphic functions. infixl 4 +<*> (+<*>) :: f (a -> a) -> f a -> f a (+<*>) = (<*>) -- | Lifted and potentially optimized monoid `mappend` operation from the parameter type. infixl 5 >< (><) :: Semigroup a => f a -> f a -> f a a >< b = (<>) <$> a +<*> b class (Alternative f, MonoidApplicative f) => MonoidAlternative f where -- | Like 'optional', but restricted to 'Monoid' results. moptional :: (Semigroup a, Monoid a) => f a -> f a moptional x = x <|> pure mempty -- | Zero or more argument occurrences like 'many', but concatenated. concatMany :: (Semigroup a, Monoid a) => f a -> f a concatMany x = many' where many' = some' <|> pure mempty some' = x >< many' -- | One or more argument occurrences like 'some', but concatenated. concatSome :: (Semigroup a, Monoid a) => f a -> f a concatSome x = some' where many' = some' <|> pure mempty some' = x >< many'