abstract-par-0.3: Type classes generalizing the functionality of the 'monad-par' library.

Safe HaskellSafe-Infered

Control.Monad.Par.Class

Contents

Description

This module establishes a class hierarchy that captures the interface(s) for valid Par monads. In particular, the functionality is split into layers: e.g. Futures vs. full IVars vs. Chans (Streams).

Not all Par monad schedulers must provide all functionality.

For more documentation of the programming model, see

Synopsis

Futures

class Monad m => ParFuture future m | m -> future where

ParFuture captures the class of Par monads which support futures. This level of functionality subsumes par/pseq and is similar to the Control.Parallel.Strategies.Eval monad.

A minimal implementation consists of spawn_ and get. However, for monads that are also a member of ParIVar it is typical to simply define spawn in terms of fork, new, and put.

Methods

spawn :: NFData a => m a -> m (future a)

Create a potentially-parallel computation, and return a future (or promise) that can be used to query the result of the forked computataion.

  spawn p = do
    r <- new
    fork (p >>= put r)
    return r

spawn_ :: m a -> m (future a)

Like spawn, but the result is only head-strict, not fully-strict.

get :: future a -> m a

spawnP :: NFData a => a -> m (future a)

Spawn a pure (rather than monadic) computation. Fully-strict.

  spawnP = spawn . return

IVars

class ParFuture ivar m => ParIVar ivar m | m -> ivar where

ParIVar builds on futures by adding full anyone-writes, anyone-reads IVars. These are more expressive but may not be supported by all distributed schedulers.

A minimal implementation consists of fork, put_, and new.

Methods

fork :: m () -> m ()

Forks a computation to happen in parallel. The forked computation may exchange values with other computations using IVars.

new :: m (ivar a)

creates a new IVar

put :: NFData a => ivar a -> a -> m ()

put a value into a IVar. Multiple puts to the same IVar are not allowed, and result in a runtime error.

put fully evaluates its argument, which therefore must be an instance of NFData. The idea is that this forces the work to happen when we expect it, rather than being passed to the consumer of the IVar and performed later, which often results in less parallelism than expected.

Sometimes partial strictness is more appropriate: see put_.

put_ :: ivar a -> a -> m ()

like put, but only head-strict rather than fully-strict.

newFull :: NFData a => a -> m (ivar a)

creates a new IVar that contains a value

newFull_ :: a -> m (ivar a)

creates a new IVar that contains a value (head-strict only)

class NFData a

A class of types that can be fully evaluated.

Instances

NFData Bool 
NFData Char 
NFData Double 
NFData Float 
NFData Int 
NFData Int8 
NFData Int16 
NFData Int32 
NFData Int64 
NFData Integer 
NFData Word 
NFData Word8 
NFData Word16 
NFData Word32 
NFData Word64 
NFData () 
NFData Version 
NFData a => NFData [a] 
(Integral a, NFData a) => NFData (Ratio a) 
NFData (Fixed a) 
(RealFloat a, NFData a) => NFData (Complex a) 
NFData a => NFData (Maybe a) 
NFData (a -> b)

This instance is for convenience and consistency with seq. This assumes that WHNF is equivalent to NF for functions.

(NFData a, NFData b) => NFData (Either a b) 
(NFData a, NFData b) => NFData (a, b) 
(Ix a, NFData a, NFData b) => NFData (Array a b) 
(NFData a, NFData b, NFData c) => NFData (a, b, c) 
(NFData a, NFData b, NFData c, NFData d) => NFData (a, b, c, d) 
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5) => NFData (a1, a2, a3, a4, a5) 
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6) => NFData (a1, a2, a3, a4, a5, a6) 
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7) => NFData (a1, a2, a3, a4, a5, a6, a7) 
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8) => NFData (a1, a2, a3, a4, a5, a6, a7, a8) 
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8, NFData a9) => NFData (a1, a2, a3, a4, a5, a6, a7, a8, a9)