@hackage speculation0.0.2

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 = 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 ----]

Changes since 0.0.1

• specFoldr1 bug fix

• Added spec' combinator

Changes since 0.0.0

• Added WithoutSpeculation and WrappedFoldable