- spec :: Eq a => a -> (a -> b) -> a -> b
- spec' :: Eq a => a -> (a -> b) -> a -> b
- evaluated :: a -> Bool
- specFoldr :: (Foldable f, Eq b) => (Int -> b) -> (a -> b -> b) -> b -> f a -> b
- specFoldl :: (Foldable f, Eq b) => (Int -> b) -> (b -> a -> b) -> b -> f a -> b
- specFoldr1 :: (Foldable f, Eq a) => (Int -> a) -> (a -> a -> a) -> f a -> a
- specFoldl1 :: (Foldable f, Eq a) => (Int -> a) -> (a -> a -> a) -> f a -> a
- specFoldrN :: (Foldable f, Eq b) => Int -> (Int -> b) -> (a -> b -> b) -> b -> f a -> b
- specFoldlN :: (Foldable f, Eq b) => Int -> (Int -> b) -> (b -> a -> b) -> b -> f a -> b

# Documentation

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

evaluates `spec`

g f a`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 ----]

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

Unlike `spec`

, this version does not check to see if the argument has already been evaluated. This can save
a small amount of work when you know the argument will always require computation.

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

Given a valid estimator `g`

,

yields the same answer as `specFoldr`

g f z xs

.
`foldr'`

f z xs

`g n`

should supply an estimate of the value returned from folding over the last `n`

elements of the container.

If `g n`

is accurate a reasonable percentage of the time and faster to compute than the fold, then this can
provide increased opportunities for parallelism.

specFoldr = specFoldrN 0

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

Given a valid estimator `g`

,

yields the same answer as `specFoldl`

g f z xs

.
`foldl'`

f z xs

`g n`

should supply an estimate of the value returned from folding over the first `n`

elements of the container.

If `g n`

is accurate a reasonable percentage of the time and faster to compute than the fold, then this can
provide increased opportunities for parallelism.

specFoldl = specFoldlN 0

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

`specFoldr1`

is to `foldr1'`

as `specFoldr`

is to `foldr'`

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

`specFoldl1`

is to `foldl1'`

as `specFoldl`

is to `foldl'`

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

Given a valid estimator `g`

,

yields the same answer as `specFoldrN`

n g f z xs

.
`foldr`

f z xs

`g m`

should supply an estimate of the value returned from folding over the last `m - n`

elements of the container.

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

Given a valid estimator `g`

,

yields the same answer as `specFoldlN`

n g f z xs

.
`foldl`

f z xs

`g m`

should supply an estimate of the value returned from folding over the first `m - n`

elements of the container.