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definition module monad
/*
Pieter Koopman, pieter@cs.ru.nl
Advanced Programming, week 4
*/
import StdMisc
class Functor f where
fmap :: (a->b) (f a) -> (f b)
(<$>) infixl 4 :: (a->b) (f a) -> (f b) | Functor f
(<$>) f x :== fmap f x
class Applicative f | Functor f where
pure :: a -> f a
(<*>) infixl 4 :: (f (a->b)) (f a) -> f b
class Monad m | Applicative m where
bind :: (m a) (a->m b) -> m b
(>>=) infixl 1 :: (m a) (a->m b) -> m b | Monad m
(>>=) a f :== bind a f
(>>|) infixl 1 :: (m a) (m b) -> m b | Monad m
(>>|) a b :== a >>= \_.b
rtrn :: a -> m a | Monad m
rtrn a :== pure a
class fail m | Applicative m where
fail :: m a
guard :: Bool -> m a | fail m
guard b :== if b (pure undef) fail
class OrMonad m where
(<|>) infixl 0 :: (m a) (m a) -> m a
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