treak
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4 changed files with 12 additions and 8 deletions
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@ -12,7 +12,7 @@ import Control.Monad (liftM)
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{- Return the first value from a list, if any, satisfying the given
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- predicate -}
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firstM :: (Monad m) => (a -> m Bool) -> [a] -> m (Maybe a)
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firstM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
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firstM _ [] = return Nothing
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firstM p (x:xs) = do
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q <- p x
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@ -22,20 +22,20 @@ firstM p (x:xs) = do
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{- Returns true if any value in the list satisfies the predicate,
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- stopping once one is found. -}
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anyM :: (Monad m) => (a -> m Bool) -> [a] -> m Bool
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anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
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anyM p = liftM isJust . firstM p
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{- Runs an action on values from a list until it succeeds. -}
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untilTrue :: (Monad m) => [a] -> (a -> m Bool) -> m Bool
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untilTrue :: Monad m => [a] -> (a -> m Bool) -> m Bool
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untilTrue = flip anyM
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{- Runs an action, passing its value to an observer before returning it. -}
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observe :: (Monad m) => (a -> m b) -> m a -> m a
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observe :: Monad m => (a -> m b) -> m a -> m a
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observe observer a = do
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r <- a
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_ <- observer r
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return r
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{- b `after` a runs first a, then b, and returns the value of a -}
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after :: (Monad m) => m b -> m a -> m a
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after :: Monad m => m b -> m a -> m a
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after = observe . const
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