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Control.Monad.Trans.Reader | Portability | portable | Stability | experimental | Maintainer | libraries@haskell.org |
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Description |
Declaration of the ReaderT monad transformer, which adds a static
environment to a given monad.
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Synopsis |
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The Reader monad
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The parameterizable reader monad.
Computations are functions of a shared environment.
The return function ignores the environment, while >>= passes
the inherited environment to both subcomputations.
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Constructor for computations in the reader monad.
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:: | | => Reader r a | A Reader to run.
| -> r | An initial environment.
| -> a | | Runs a Reader and extracts the final value from it.
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Transform the value returned by a Reader.
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:: | | => r' -> r | The function to modify the environment.
| -> Reader r a | Computation to run in the modified environment.
| -> Reader r' a | | Execute a computation in a modified environment
(a specialization of withReaderT).
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The ReaderT monad transformer
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The reader monad transformer,
which adds a read-only environment to the given monad.
The return function ignores the environment, while >>= passes
the inherited environment to both subcomputations.
| Constructors | ReaderT | | runReaderT :: r -> m a | The underlying computation, as a function of the environment.
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| Instances | |
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Transform the computation inside a ReaderT.
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:: | | => r' -> r | The function to modify the environment.
| -> ReaderT r m a | Computation to run in the modified environment.
| -> ReaderT r' m a | | Execute a computation in a modified environment
(a more general version of local).
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Reader operations
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Fetch the value of the environment.
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:: Monad m | | => r -> r | The function to modify the environment.
| -> ReaderT r m a | Computation to run in the modified environment.
| -> ReaderT r m a | | Execute a computation in a modified environment
(a specialization of withReaderT).
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:: Monad m | | => r -> a | The selector function to apply to the environment.
| -> ReaderT r m a | | Retrieve a function of the current environment.
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Lifting other operations
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:: | | => ((a -> m b) -> m a) -> m a | callCC on the argument monad.
| -> (a -> ReaderT r m b) -> ReaderT r m a | | -> ReaderT r m a | | Lift a callCC operation to the new monad.
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:: | | => m a -> (e -> m a) -> m a | catch on the argument monad.
| -> ReaderT r m a | Computation to attempt.
| -> e -> ReaderT r m a | Exception handler.
| -> ReaderT r m a | | Lift a catchError operation to the new monad.
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Produced by Haddock version 2.4.2 |