27 lines
659 B
Haskell
27 lines
659 B
Haskell
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{- state monad support
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-
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- Copyright 2012 Joey Hess <joey@kitenet.net>
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-
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- Licensed under the GNU GPL version 3 or higher.
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-}
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module Utility.State where
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import Control.Monad.State.Strict
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{- Modifies Control.Monad.State's state, forcing a strict update.
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- This avoids building thunks in the state and leaking.
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- Why it's not the default, I don't know.
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-
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- Example: changeState $ \s -> s { foo = bar }
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-}
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changeState :: MonadState s m => (s -> s) -> m ()
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changeState f = do
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x <- get
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put $! f x
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{- Gets a value from the internal state, selected by the passed value
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- constructor. -}
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getState :: MonadState s m => (s -> a) -> m a
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getState = gets
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