Monad.hs

module Test.Abides.Control.Monad where

import Control.Monad (MonadPlus (mzero, mplus))
import qualified Test.Abides.Properties as P


leftIdentity :: Monad m => Eq (m b) => (a -> m b) -> a -> Bool
leftIdentity f x = (pure x >>= f) == f x


rightIdentity :: Monad m => Eq (m a) => m a -> Bool
rightIdentity x = (x >>= pure) == x


associative :: Monad m => Eq (m c) => (a -> m b) -> (b -> m c) -> m a -> Bool
associative f g x = ((x >>= f) >>= g) == (x >>= (\k -> f k >>= g))


annihilation :: MonadPlus m => Eq (m b) => (a -> m b) -> Bool
annihilation f = (mzero >>= f) == mzero


distributive :: MonadPlus m => Eq (m b) => (a -> m b) -> m a -> m a -> Bool
distributive f = P.distributive' (>>= f) mplus mplus