 spec :: Eq a => a > (a > b) > a > b
 spec' :: Eq a => a > (a > b) > a > b
 specBy :: (a > a > Bool) > a > (a > b) > a > b
 specBy' :: (a > a > Bool) > a > (a > b) > a > b
 specOn :: Eq c => (a > c) > a > (a > b) > a > b
 specOn' :: Eq c => (a > c) > a > (a > b) > a > b
 specSTM :: Eq a => a > (a > STM b) > a > STM b
 specSTM' :: Eq a => a > (a > STM b) > a > STM b
 specOnSTM :: Eq c => (a > c) > a > (a > STM b) > a > STM b
 specOnSTM' :: Eq c => (a > c) > a > (a > STM b) > a > STM b
 specBySTM :: (a > a > Bool) > a > (a > STM b) > a > STM b
 specBySTM' :: (a > a > Bool) > a > (a > STM b) > a > STM b
 specCSTM :: Eq a => a > (a > CSTM b) > a > CSTM b
 specCSTM' :: Eq a => a > (a > CSTM b) > a > CSTM b
 specOnCSTM :: Eq c => (a > c) > a > (a > CSTM b) > a > CSTM b
 specOnCSTM' :: Eq c => (a > c) > a > (a > CSTM b) > a > CSTM b
 specByCSTM :: (a > a > Bool) > a > (a > CSTM b) > a > CSTM b
 specByCSTM' :: (a > a > Bool) > a > (a > CSTM b) > a > CSTM b
 type CSTM = Codensity STM
 newtype Codensity f a = Codensity {
 runCodensity :: forall r. (a > f r) > f r
 liftCodensity :: Monad m => m a > Codensity m a
 lowerCodensity :: Monad m => Codensity m a > m a
Speculative application
spec :: Eq a => a > (a > b) > a > bSource
evaluates spec
g f af 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 bestcase timeline looks like:
[ f g ] [ a ] [ spec g f a ]
The worstcase 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.
specBy :: (a > a > Bool) > a > (a > b) > a > bSource
spec
with a user defined comparison function
specBy' :: (a > a > Bool) > a > (a > b) > a > bSource
spec'
with a user defined comparison function
specOn :: Eq c => (a > c) > a > (a > b) > a > bSource
spec
comparing by projection onto another type
specOn' :: Eq c => (a > c) > a > (a > b) > a > bSource
spec'
comparing by projection onto another type
Speculative application with transactional rollback
specSTM :: Eq a => a > (a > STM b) > a > STM bSource
evaluates specSTM
g f af g
while forcing a
, if g == a
then f g
is returned. Otherwise the sideeffects
of the current STM transaction are rolled back and f a
is evaluated.
If the argument a
is already evaluated, we don't bother to perform f g
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.
specSTM a f a = f $! a
The bestcase timeline looks like:
[ f g ] [ a ] [ specSTM g f a ]
The worstcase timeline looks like:
[ f g ] [ a ] [ rollback ] [ f a ] [ spec g f a ]
Compare these to the timeline of f $! a
:
[ a ] [ f a ]
specOnSTM' :: Eq c => (a > c) > a > (a > STM b) > a > STM bSource
specBySTM'
. on
(==)'
specBySTM :: (a > a > Bool) > a > (a > STM b) > a > STM bSource
specSTM
using a user defined comparison function
specBySTM' :: (a > a > Bool) > a > (a > STM b) > a > STM bSource
specSTM'
using a user defined comparison function
Codensity STM speculation
specOnCSTM :: Eq c => (a > c) > a > (a > CSTM b) > a > CSTM bSource
specByCSTM
. on
(==)'
specOnCSTM' :: Eq c => (a > c) > a > (a > CSTM b) > a > CSTM bSource
specByCSTM'
. on
(==)'
specByCSTM :: (a > a > Bool) > a > (a > CSTM b) > a > CSTM bSource
specSTM
using a user defined comparison function
specByCSTM' :: (a > a > Bool) > a > (a > CSTM b) > a > CSTM bSource
specCSTM'
using a user defined comparison function
Codensity
Codensity  

liftCodensity :: Monad m => m a > Codensity m aSource
lowerCodensity :: Monad m => Codensity m a > m aSource