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| Description |
Author : Ralf Laemmel, Joost Visser
Stability : experimental
Portability : portable
This module is part of StrategyLib, a library of functional strategy
combinators, including combinators for generic traversal. This module
provides non-strategic functionality for running monads and unlifting
monad transformers. In a sense, this is dual to the return and lift
functionality of the Monad and MonadTrans classes.
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| Synopsis |
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| data MaybeAlg a b = MaybeAlg {} | | | data ErrorAlg e a b = ErrorAlg {} | | | data ListAlg a b = ListAlg {} | | | data StateAlg s a b = StateAlg {} | | | class MonadRun s m | m -> s where | | | | mrun :: (MonadRun s m, Monad m') => s a b -> m a -> m' b | | | class MonadUnTrans s t | t -> s where | | | | mplus' :: (Monad m, MonadUnTrans MaybeAlg t) => t m b -> m b -> m b | | | mswitch :: (Monad m, MonadUnTrans MaybeAlg t) => [t m b] -> m b -> m b | | | mayswitch :: Monad m => [MaybeT m b] -> m b -> m b | | | mchoice' :: (Monad m, MonadUnTrans MaybeAlg t) => (a -> t m b) -> (a -> m b) -> a -> m b | | | mchoices :: (Monad m, MonadUnTrans MaybeAlg t, MonadPlus (t m)) => [a -> t m b] -> (a -> m b) -> a -> m b | | | mswitch0 :: (Monad m, MonadUnTrans MaybeAlg t) => [t m b] -> m b -> m b | | | mswitch1 :: (Monad m, MonadUnTrans MaybeAlg t) => [t m b] -> m b -> m b | | | mswitch' :: (Monad m, MonadUnTrans MaybeAlg t, MonadPlus (t m)) => [t m b] -> m b -> m b |
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| Monad algebras
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| data MaybeAlg a b |
| The algebra for the partiality effect of Maybe and MaybeT.
| | Constructors | | MaybeAlg | | | nothing :: b | | | just :: (a -> b) | |
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|  Instances | |
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| data ErrorAlg e a b |
| The algebra for the error effect of Either and ErrorT.
| | Constructors | | ErrorAlg | | | left :: (e -> b) | | | right :: (a -> b) | |
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| | Instances | |
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| data ListAlg a b |
| The algebra for the non-determinacy effect of '[]' and ListT.
| | Constructors | | ListAlg | | | nil :: b | | | cons :: (a -> b -> b) | |
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| | Instances | |
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| data StateAlg s a b |
| The algebra for the state effect of State and StateT.
| | Constructors | | StateAlg | | | first :: s | initial state
| | next :: ((a, s) -> b) | state transformer
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| | Instances | |
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| Running monads
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| class MonadRun s m | m -> s where |
| The class of monads for which a run function is defined that
executes the computation of the monad.
| | | Methods | | run :: s a b -> m a -> b | | The overloaded function run takes as first argument an algebra which
captures the ingredients necessary to run the particular monad at hand.
This algebra is parameterized with the domain and co-domain of run.
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| mrun :: (MonadRun s m, Monad m') => s a b -> m a -> m' b |
| Exchange one monad by another.
This function runs one monad, and puts its value in another. This is
basically a monadic version of the run function itself. Note that the two
monads are unrelated, so none of the effects of the incoming monad are
transferred to the result monad.
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| Unlifting monad transformers
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| class MonadUnTrans s t | t -> s where |
| Just as a base monad can be run to remove the monad, so can a transformed
monad be unlifted to remove the transformer and obtain the original monad.
| | | Methods | | unlift :: Monad m => s a b -> t m a -> m b | | The overloaded function unlift for monad transformers takes as first
argument an algebra just like the run function for base monads. For
each monad transformer, the same algebra is used as for the base monad
of which the transformer is the parameterized variant.
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| Monadic choice combinators that confine the partiality effect
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| Monadic choice
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| mplus' :: (Monad m, MonadUnTrans MaybeAlg t) => t m b -> m b -> m b |
| Monadic choice combinator that confines the partiality effect to
the first argument. This is a variation on mplus which allows
the partiality effect to spread to both arguments and to the result.
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| mswitch |
| :: (Monad m, MonadUnTrans MaybeAlg t) | | | => [t m b] | choice branches
| | -> m b | otherwise
| | -> m b | result
| | Monadic choice combinator. Generalization of mplus' that takes a list
of choice arguments rather than a single one.
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| mayswitch :: Monad m => [MaybeT m b] -> m b -> m b |
| Specialization of mswitch for MaybeT.
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| Monadic function choice
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| mchoice' :: (Monad m, MonadUnTrans MaybeAlg t) => (a -> t m b) -> (a -> m b) -> a -> m b |
| Monadic function choice combinator that confines the partiality effect
to the first argument. This is a variation on mchoice which
allows the partiality effect to spread to both arguments and to the
result.
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| mchoices :: (Monad m, MonadUnTrans MaybeAlg t, MonadPlus (t m)) => [a -> t m b] -> (a -> m b) -> a -> m b |
| Monadic function choice combinator. Generalization of mchoice' that
takes a list of choice arguments rather than a single one.
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| Implementation variants
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| mswitch0 :: (Monad m, MonadUnTrans MaybeAlg t) => [t m b] -> m b -> m b |
| Implementation variant of mswitch in terms of foldr.
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| mswitch1 :: (Monad m, MonadUnTrans MaybeAlg t) => [t m b] -> m b -> m b |
| Implementation variant of mswitch with mplus' expanded:
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| mswitch' :: (Monad m, MonadUnTrans MaybeAlg t, MonadPlus (t m)) => [t m b] -> m b -> m b |
| Implementation variant of mswitch where the unlift is postponed
to the very end.
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| Produced by Haddock version 0.8 |
