Safe Haskell | None |
---|---|

Language | Haskell2010 |

This module defines classes of monads that can perform multiple computations in parallel and, more importantly, combine the results of those parallel computations.

There are two classes exported by this module, `MonadParallel`

and `MonadFork`

. The former is more generic, but the
latter is easier to use: when invoking any expensive computation that could be performed in parallel, simply wrap the
call in `forkExec`

. The function immediately returns a handle to the running computation. The handle can be used to
obtain the result of the computation when needed:

do child <- forkExec expensive otherStuff result <- child

In this example, the computations *expensive* and *otherStuff* would be performed in parallel. When using the
`MonadParallel`

class, both parallel computations must be specified at once:

bindM2 (\ childResult otherResult -> ...) expensive otherStuff

In either case, for best results the costs of the two computations should be roughly equal.

Any monad that is an instance of the `MonadFork`

class is also an instance of the `MonadParallel`

class, and the
following law should hold:

bindM2 f ma mb = do {a' <- forkExec ma; b <- mb; a <- a'; f a b}

When operating with monads free of side-effects, such as `Identity`

or `Maybe`

, `forkExec`

is equivalent to `return`

and `bindM2`

is equivalent to ` \ f ma mb -> do {a <- ma; b <- mb; f a b} `

— the only difference is in the
resource utilisation. With the `IO`

monad, on the other hand, there may be visible difference in the results because
the side effects of *ma* and *mb* may be arbitrarily reordered.

- class Monad m => MonadParallel m where
- bindM2 :: (a -> b -> m c) -> m a -> m b -> m c

- class MonadParallel m => MonadFork m where
- forkExec :: m a -> m (m a)

- bindM3 :: MonadParallel m => (a -> b -> c -> m d) -> m a -> m b -> m c -> m d
- liftM2 :: MonadParallel m => (a -> b -> c) -> m a -> m b -> m c
- liftM3 :: MonadParallel m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r
- ap :: MonadParallel m => m (a -> b) -> m a -> m b
- sequence :: MonadParallel m => [m a] -> m [a]
- sequence_ :: MonadParallel m => [m a] -> m ()
- mapM :: MonadParallel m => (a -> m b) -> [a] -> m [b]
- replicateM :: MonadParallel m => Int -> m a -> m [a]
- replicateM_ :: MonadParallel m => Int -> m a -> m ()

# Classes

class Monad m => MonadParallel m where Source

Class of monads that can perform two computations in parallel and bind their results together.

Nothing

bindM2 :: (a -> b -> m c) -> m a -> m b -> m c Source

Perform two monadic computations in parallel; when they are both finished, pass the results to the function.
Apart from the possible ordering of side effects, this function is equivalent to
`\f ma mb-> do {a <- ma; b <- mb; f a b}`

MonadParallel [] Source | |

MonadParallel IO Source | IO is parallelizable by |

MonadParallel Identity Source | Any monad that allows the result value to be extracted, such as |

MonadParallel Maybe Source | |

MonadParallel ((->) r) Source | |

MonadParallel m => MonadParallel (MaybeT m) Source | |

MonadParallel m => MonadParallel (ListT m) Source | |

MonadParallel m => MonadParallel (IdentityT m) Source | |

MonadParallel m => MonadParallel (ExceptT e m) Source | |

MonadParallel m => MonadParallel (ReaderT r m) Source |

class MonadParallel m => MonadFork m where Source

Class of monads that can fork a parallel computation.

Nothing

forkExec :: m a -> m (m a) Source

Fork a child monadic computation to be performed in parallel with the current one.

MonadFork [] Source | |

MonadFork IO Source | IO is forkable by |

MonadFork Maybe Source | |

MonadFork ((->) r) Source | |

MonadFork m => MonadFork (MaybeT m) Source | |

MonadFork m => MonadFork (ListT m) Source | |

MonadFork m => MonadFork (IdentityT m) Source | |

MonadFork m => MonadFork (ExceptT e m) Source | |

MonadFork m => MonadFork (ReaderT r m) Source |

bindM3 :: MonadParallel m => (a -> b -> c -> m d) -> m a -> m b -> m c -> m d Source

Perform three monadic computations in parallel; when they are all finished, pass their results to the function.

# Control.Monad equivalents

liftM2 :: MonadParallel m => (a -> b -> c) -> m a -> m b -> m c Source

Like `liftM2`

, but evaluating its two monadic arguments in parallel.

liftM3 :: MonadParallel m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r Source

Like `liftM3`

, but evaluating its three monadic arguments in parallel.

ap :: MonadParallel m => m (a -> b) -> m a -> m b Source

Like `ap`

, but evaluating the function and its argument in parallel.

sequence :: MonadParallel m => [m a] -> m [a] Source

Like `sequence`

, but executing the actions in parallel.

sequence_ :: MonadParallel m => [m a] -> m () Source

Like `sequence_`

, but executing the actions in parallel.

mapM :: MonadParallel m => (a -> m b) -> [a] -> m [b] Source

Like `mapM`

, but applying the function to the individual list items in parallel.

replicateM :: MonadParallel m => Int -> m a -> m [a] Source

Like `replicateM`

, but executing the action multiple times in parallel.

replicateM_ :: MonadParallel m => Int -> m a -> m () Source

Like `replicateM_`

, but executing the action multiple times in parallel.