speculation-0.0.2: A framework for safe, programmable, speculative parallelism

Control.Concurrent.Speculation

Synopsis

# Documentation

spec :: Eq a => a -> (a -> b) -> a -> bSource

`spec g f a` evaluates `f g` while forcing `a`, if `g == a` then `f g` is returned. Otherwise `f a` is evaluated.

Furthermore, if the argument has already been evaluated, we avoid sparking the parallel computation at all.

If a good guess at the value of `a` is available, this is one way to induce parallelism in an otherwise sequential task.

However, if the guess isn't available more cheaply than the actual answer, then this saves no work and if the guess is wrong, you risk evaluating the function twice.

``` spec a f a = a `seq` f a
```

The best-case timeline looks like:

``` [---- f g ----]
[----- a -----]
[-- spec g f a --]
```

The worst-case timeline looks like:

``` [---- f g ----]
[----- a -----]
[---- f a ----]
[------- spec g f a -----------]
```

Compared to the unspeculated timeline of

``` [---- a -----]
[---- f a ----]
```

spec' :: Eq a => a -> (a -> b) -> a -> bSource

`spec' g f a` evaluates a function `f ` using a cheap guess `g` at the argument in parallel with forcing the argument.

This is one way to induce parallelism in an otherwise sequential task. Unlike `spec` this version does not check to see if the argument has already been evaluated before evaluating the speculated version. This is useful when you know `evaluated` will always return False.

The following identity holds:

``` spec' a f a = a `seq` f a
```

evaluated :: a -> BoolSource

Returns a guess as to whether or not a value has been evaluated. This is an impure function that relies on GHC internals and will return false negatives, but (hopefully) no false positives.

specFoldr :: (Speculative f, Eq b) => (Int -> b) -> (a -> b -> b) -> b -> f a -> bSource

Compute a right biased fold. The estimator function provides a guess at the value of the suffix

specFoldl :: (Speculative f, Eq b) => (Int -> b) -> (b -> a -> b) -> b -> f a -> bSource

Compute a left-biased fold. The estimator function provides a guess at the value of the prefix

class Foldable f => Speculative f whereSource

Methods

specFoldr1 :: Eq a => (Int -> a) -> (a -> a -> a) -> f a -> aSource

Compute a right-biased fold. The estimator function is a guess at the value of the prefix

specFoldrN :: Eq b => Int -> (Int -> b) -> (a -> b -> b) -> b -> f a -> bSource

specFoldl1 :: Eq a => (Int -> a) -> (a -> a -> a) -> f a -> aSource

Compute a left biased fold. the estimator function is a guess at the value of the prefix

specFoldlN :: Eq b => Int -> (Int -> b) -> (b -> a -> b) -> b -> f a -> bSource

Instances

 Speculative [] Speculative Maybe Speculative IntMap Speculative Set Speculative Seq Ix i => Speculative (Array i) Speculative (Map a) Foldable f => Speculative (WithoutSpeculation f) Foldable f => Speculative (WrappedFoldable f)

newtype WrappedFoldable f a Source

Constructors

 WrappedFoldable FieldsgetWrappedFoldable :: f a

Instances

 Functor f => Functor (WrappedFoldable f) Typeable1 f => Typeable1 (WrappedFoldable f) Foldable f => Foldable (WrappedFoldable f) Traversable f => Traversable (WrappedFoldable f) Foldable f => Speculative (WrappedFoldable f) (Typeable1 f, Data (f a), Data a) => Data (WrappedFoldable f a)

newtype WithoutSpeculation f a Source

Constructors

 WithoutSpeculation FieldsgetWithoutSpeculation :: f a

Instances

 Functor f => Functor (WithoutSpeculation f) Typeable1 f => Typeable1 (WithoutSpeculation f) Foldable f => Foldable (WithoutSpeculation f) Traversable f => Traversable (WithoutSpeculation f) Foldable f => Speculative (WithoutSpeculation f) (Typeable1 f, Data (f a), Data a) => Data (WithoutSpeculation f a)