@hackage speculation0.1.0

A framework for safe, programmable, speculative parallelism, loosely based on http://research.microsoft.com/pubs/118795/pldi026-vaswani.pdf

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 = 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 -----------]

Compare these to the timeline of f $! a:

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

specSTM provides a similar time table for STM actions, but also rolls back side-effects.

Changes in 0.1.0:

• Added Control.Concurrent.STM.Speculation with specSTM, and specSTM'

Changes in 0.0.2:

• specFoldr1 bug fix

• Added spec' combinator

Changes in 0.0.1:

• Added WithoutSpeculation and WrappedFoldable