# Proposal: Strict variant of foldMap

9 messages
Open this post in threaded view
|

## Proposal: Strict variant of foldMap

 I propose adding another method to the Foldable typeclass: foldMap'This has the same behavior as foldMap except that it is strict in the accumulator. This can lead to considerable performance gains when the user knows that monoidal append is strict both arguments. Consider the following example (available as a gist at https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955):  {-# LANGUAGE BangPatterns #-}  {-# OPTIONS_GHC -O2 #-}  import Gauge  import Data.Foldable  import qualified Data.Set as S    foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m  foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty  numbers :: [Int]  numbers = [1..4000]    intToSet :: Int -> S.Set Int  intToSet i = S.singleton (mod i 10)  main :: IO ()  main = defaultMain    [ bench "lazy" \$ whnf (foldMap intToSet) numbers    , bench "strict" \$ whnf (foldMap' intToSet) numbers    ]Here are the results we get from running this:  benchmarked lazy  time                 178.8 μs   (176.1 μs .. 183.1 μs)                       0.996 R²   (0.993 R² .. 0.998 R²)  mean                 180.8 μs   (179.1 μs .. 183.3 μs)  std dev              7.242 μs   (5.856 μs .. 9.304 μs)  variance introduced by outliers: 20% (moderately inflated)  benchmarked strict  time                 108.4 μs   (106.1 μs .. 111.0 μs)                       0.997 R²   (0.996 R² .. 0.999 R²)  mean                 107.9 μs   (107.0 μs .. 109.3 μs)  std dev              3.672 μs   (2.451 μs .. 6.220 μs)  variance introduced by outliers: 15% (moderately inflated)These performance gains are considerable. It needs to be a method of Foldable and not just a function written using foldl' for the same reason that the lazy foldMap needs to be a method of Foldable. There are types for which the default implementation can be improved upon. This is a non-breaking change since there is a sensible default implementation.-- -Andrew Thaddeus Martin _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Open this post in threaded view
|

## Re: Proposal: Strict variant of foldMap

 I'm in favor of adding this to Foldable. 2018-06-08 15:20 GMT+02:00 Andrew Martin <[hidden email]>: > I propose adding another method to the Foldable typeclass: foldMap' > > This has the same behavior as foldMap except that it is strict in the > accumulator. This can lead to considerable performance gains when the user > knows that monoidal append is strict both arguments. Consider the following > example (available as a gist at > https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955):> >   {-# LANGUAGE BangPatterns #-} >   {-# OPTIONS_GHC -O2 #-} >   import Gauge >   import Data.Foldable >   import qualified Data.Set as S > >   foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m >   foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty > >   numbers :: [Int] >   numbers = [1..4000] > >   intToSet :: Int -> S.Set Int >   intToSet i = S.singleton (mod i 10) > >   main :: IO () >   main = defaultMain >     [ bench "lazy" \$ whnf (foldMap intToSet) numbers >     , bench "strict" \$ whnf (foldMap' intToSet) numbers >     ] > > Here are the results we get from running this: > >   benchmarked lazy >   time                 178.8 μs   (176.1 μs .. 183.1 μs) >                        0.996 R²   (0.993 R² .. 0.998 R²) >   mean                 180.8 μs   (179.1 μs .. 183.3 μs) >   std dev              7.242 μs   (5.856 μs .. 9.304 μs) >   variance introduced by outliers: 20% (moderately inflated) > >   benchmarked strict >   time                 108.4 μs   (106.1 μs .. 111.0 μs) >                        0.997 R²   (0.996 R² .. 0.999 R²) >   mean                 107.9 μs   (107.0 μs .. 109.3 μs) >   std dev              3.672 μs   (2.451 μs .. 6.220 μs) >   variance introduced by outliers: 15% (moderately inflated) > > These performance gains are considerable. It needs to be a method of > Foldable and not just a function written using foldl' for the same reason > that the lazy foldMap needs to be a method of Foldable. There are types for > which the default implementation can be improved upon. This is a > non-breaking change since there is a sensible default implementation. > > -- > -Andrew Thaddeus Martin > > _______________________________________________ > Libraries mailing list > [hidden email] > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries> _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Open this post in threaded view
|

## Re: Proposal: Strict variant of foldMap

 +1On Fri, Jun 8, 2018, 7:10 AM Simon Jakobi via Libraries <[hidden email]> wrote:I'm in favor of adding this to Foldable. 2018-06-08 15:20 GMT+02:00 Andrew Martin <[hidden email]>: > I propose adding another method to the Foldable typeclass: foldMap' > > This has the same behavior as foldMap except that it is strict in the > accumulator. This can lead to considerable performance gains when the user > knows that monoidal append is strict both arguments. Consider the following > example (available as a gist at > https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955): > >   {-# LANGUAGE BangPatterns #-} >   {-# OPTIONS_GHC -O2 #-} >   import Gauge >   import Data.Foldable >   import qualified Data.Set as S > >   foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m >   foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty > >   numbers :: [Int] >   numbers = [1..4000] > >   intToSet :: Int -> S.Set Int >   intToSet i = S.singleton (mod i 10) > >   main :: IO () >   main = defaultMain >     [ bench "lazy" \$ whnf (foldMap intToSet) numbers >     , bench "strict" \$ whnf (foldMap' intToSet) numbers >     ] > > Here are the results we get from running this: > >   benchmarked lazy >   time                 178.8 μs   (176.1 μs .. 183.1 μs) >                        0.996 R²   (0.993 R² .. 0.998 R²) >   mean                 180.8 μs   (179.1 μs .. 183.3 μs) >   std dev              7.242 μs   (5.856 μs .. 9.304 μs) >   variance introduced by outliers: 20% (moderately inflated) > >   benchmarked strict >   time                 108.4 μs   (106.1 μs .. 111.0 μs) >                        0.997 R²   (0.996 R² .. 0.999 R²) >   mean                 107.9 μs   (107.0 μs .. 109.3 μs) >   std dev              3.672 μs   (2.451 μs .. 6.220 μs) >   variance introduced by outliers: 15% (moderately inflated) > > These performance gains are considerable. It needs to be a method of > Foldable and not just a function written using foldl' for the same reason > that the lazy foldMap needs to be a method of Foldable. There are types for > which the default implementation can be improved upon. This is a > non-breaking change since there is a sensible default implementation. > > -- > -Andrew Thaddeus Martin > > _______________________________________________ > Libraries mailing list > [hidden email] > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries > _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Open this post in threaded view
|

## Re: Proposal: Strict variant of foldMap

 In reply to this post by Andrew Martin +1On Fri, Jun 8, 2018 at 9:20 AM Andrew Martin <[hidden email]> wrote:I propose adding another method to the Foldable typeclass: foldMap'This has the same behavior as foldMap except that it is strict in the accumulator. This can lead to considerable performance gains when the user knows that monoidal append is strict both arguments. Consider the following example (available as a gist at https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955):  {-# LANGUAGE BangPatterns #-}  {-# OPTIONS_GHC -O2 #-}  import Gauge  import Data.Foldable  import qualified Data.Set as S    foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m  foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty  numbers :: [Int]  numbers = [1..4000]    intToSet :: Int -> S.Set Int  intToSet i = S.singleton (mod i 10)  main :: IO ()  main = defaultMain    [ bench "lazy" \$ whnf (foldMap intToSet) numbers    , bench "strict" \$ whnf (foldMap' intToSet) numbers    ]Here are the results we get from running this:  benchmarked lazy  time                 178.8 μs   (176.1 μs .. 183.1 μs)                       0.996 R²   (0.993 R² .. 0.998 R²)  mean                 180.8 μs   (179.1 μs .. 183.3 μs)  std dev              7.242 μs   (5.856 μs .. 9.304 μs)  variance introduced by outliers: 20% (moderately inflated)  benchmarked strict  time                 108.4 μs   (106.1 μs .. 111.0 μs)                       0.997 R²   (0.996 R² .. 0.999 R²)  mean                 107.9 μs   (107.0 μs .. 109.3 μs)  std dev              3.672 μs   (2.451 μs .. 6.220 μs)  variance introduced by outliers: 15% (moderately inflated)These performance gains are considerable. It needs to be a method of Foldable and not just a function written using foldl' for the same reason that the lazy foldMap needs to be a method of Foldable. There are types for which the default implementation can be improved upon. This is a non-breaking change since there is a sensible default implementation.-- -Andrew Thaddeus Martin _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Open this post in threaded view
|

## Re: Proposal: Strict variant of foldMap

 +1 We utilize a foldMap' in the freckle codebase.On Fri, Jun 8, 2018 at 1:10 PM, Daniel Cartwright wrote:+1On Fri, Jun 8, 2018 at 9:20 AM Andrew Martin <[hidden email]> wrote:I propose adding another method to the Foldable typeclass: foldMap'This has the same behavior as foldMap except that it is strict in the accumulator. This can lead to considerable performance gains when the user knows that monoidal append is strict both arguments. Consider the following example (available as a gist at https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955):  {-# LANGUAGE BangPatterns #-}  {-# OPTIONS_GHC -O2 #-}  import Gauge  import Data.Foldable  import qualified Data.Set as S    foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m  foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty  numbers :: [Int]  numbers = [1..4000]    intToSet :: Int -> S.Set Int  intToSet i = S.singleton (mod i 10)  main :: IO ()  main = defaultMain    [ bench "lazy" \$ whnf (foldMap intToSet) numbers    , bench "strict" \$ whnf (foldMap' intToSet) numbers    ]Here are the results we get from running this:  benchmarked lazy  time                 178.8 μs   (176.1 μs .. 183.1 μs)                       0.996 R²   (0.993 R² .. 0.998 R²)  mean                 180.8 μs   (179.1 μs .. 183.3 μs)  std dev              7.242 μs   (5.856 μs .. 9.304 μs)  variance introduced by outliers: 20% (moderately inflated)  benchmarked strict  time                 108.4 μs   (106.1 μs .. 111.0 μs)                       0.997 R²   (0.996 R² .. 0.999 R²)  mean                 107.9 μs   (107.0 μs .. 109.3 μs)  std dev              3.672 μs   (2.451 μs .. 6.220 μs)  variance introduced by outliers: 15% (moderately inflated)These performance gains are considerable. It needs to be a method of Foldable and not just a function written using foldl' for the same reason that the lazy foldMap needs to be a method of Foldable. There are types for which the default implementation can be improved upon. This is a non-breaking change since there is a sensible default implementation.-- -Andrew Thaddeus Martin _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries -- --Evan Borden _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Open this post in threaded view
|

## Re: Proposal: Strict variant of foldMap

 +1 from me.-EdwardOn Jun 8, 2018, at 9:11 PM, [hidden email] <[hidden email]> wrote:+1 We utilize a foldMap' in the freckle codebase.On Fri, Jun 8, 2018 at 1:10 PM, Daniel Cartwright wrote:+1On Fri, Jun 8, 2018 at 9:20 AM Andrew Martin <[hidden email]> wrote:I propose adding another method to the Foldable typeclass: foldMap'This has the same behavior as foldMap except that it is strict in the accumulator. This can lead to considerable performance gains when the user knows that monoidal append is strict both arguments. Consider the following example (available as a gist at https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955):  {-# LANGUAGE BangPatterns #-}  {-# OPTIONS_GHC -O2 #-}  import Gauge  import Data.Foldable  import qualified Data.Set as S    foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m  foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty  numbers :: [Int]  numbers = [1..4000]    intToSet :: Int -> S.Set Int  intToSet i = S.singleton (mod i 10)  main :: IO ()  main = defaultMain    [ bench "lazy" \$ whnf (foldMap intToSet) numbers    , bench "strict" \$ whnf (foldMap' intToSet) numbers    ]Here are the results we get from running this:  benchmarked lazy  time                 178.8 μs   (176.1 μs .. 183.1 μs)                       0.996 R²   (0.993 R² .. 0.998 R²)  mean                 180.8 μs   (179.1 μs .. 183.3 μs)  std dev              7.242 μs   (5.856 μs .. 9.304 μs)  variance introduced by outliers: 20% (moderately inflated)  benchmarked strict  time                 108.4 μs   (106.1 μs .. 111.0 μs)                       0.997 R²   (0.996 R² .. 0.999 R²)  mean                 107.9 μs   (107.0 μs .. 109.3 μs)  std dev              3.672 μs   (2.451 μs .. 6.220 μs)  variance introduced by outliers: 15% (moderately inflated)These performance gains are considerable. It needs to be a method of Foldable and not just a function written using foldl' for the same reason that the lazy foldMap needs to be a method of Foldable. There are types for which the default implementation can be improved upon. This is a non-breaking change since there is a sensible default implementation.-- -Andrew Thaddeus Martin _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries -- --Evan Borden _______________________________________________Libraries mailing list[hidden email]http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries_______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Open this post in threaded view
|

## Re: Proposal: Strict variant of foldMap

 Is there any chance that foldMap' might still make it into base-4.12? Am Sa., 9. Juni 2018 um 10:23 Uhr schrieb Edward Kmett <[hidden email]>: > > +1 from me. > > -Edward > > On Jun 8, 2018, at 9:11 PM, [hidden email] <[hidden email]> wrote: > > +1 We utilize a foldMap' in the freckle codebase. > > On Fri, Jun 8, 2018 at 1:10 PM, Daniel Cartwright <[hidden email]> wrote: >> >> +1 >> >> On Fri, Jun 8, 2018 at 9:20 AM Andrew Martin <[hidden email]> wrote: >>> >>> I propose adding another method to the Foldable typeclass: foldMap' >>> >>> This has the same behavior as foldMap except that it is strict in the accumulator. This can lead to considerable performance gains when the user knows that monoidal append is strict both arguments. Consider the following example (available as a gist at https://gist.github.com/andrewthad/f79b7022725532baf709514cf08c3955):>>> >>>   {-# LANGUAGE BangPatterns #-} >>>   {-# OPTIONS_GHC -O2 #-} >>>   import Gauge >>>   import Data.Foldable >>>   import qualified Data.Set as S >>> >>>   foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m >>>   foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty >>> >>>   numbers :: [Int] >>>   numbers = [1..4000] >>> >>>   intToSet :: Int -> S.Set Int >>>   intToSet i = S.singleton (mod i 10) >>> >>>   main :: IO () >>>   main = defaultMain >>>     [ bench "lazy" \$ whnf (foldMap intToSet) numbers >>>     , bench "strict" \$ whnf (foldMap' intToSet) numbers >>>     ] >>> >>> Here are the results we get from running this: >>> >>>   benchmarked lazy >>>   time                 178.8 μs   (176.1 μs .. 183.1 μs) >>>                        0.996 R²   (0.993 R² .. 0.998 R²) >>>   mean                 180.8 μs   (179.1 μs .. 183.3 μs) >>>   std dev              7.242 μs   (5.856 μs .. 9.304 μs) >>>   variance introduced by outliers: 20% (moderately inflated) >>> >>>   benchmarked strict >>>   time                 108.4 μs   (106.1 μs .. 111.0 μs) >>>                        0.997 R²   (0.996 R² .. 0.999 R²) >>>   mean                 107.9 μs   (107.0 μs .. 109.3 μs) >>>   std dev              3.672 μs   (2.451 μs .. 6.220 μs) >>>   variance introduced by outliers: 15% (moderately inflated) >>> >>> These performance gains are considerable. It needs to be a method of Foldable and not just a function written using foldl' for the same reason that the lazy foldMap needs to be a method of Foldable. There are types for which the default implementation can be improved upon. This is a non-breaking change since there is a sensible default implementation. >>> >>> -- >>> -Andrew Thaddeus Martin >>> _______________________________________________ >>> Libraries mailing list >>> [hidden email] >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries>> >> >> _______________________________________________ >> Libraries mailing list >> [hidden email] >> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries>> > > > > -- > -- > Evan Borden > > _______________________________________________ > Libraries mailing list > [hidden email] > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries> > _______________________________________________ > Libraries mailing list > [hidden email] > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries_______________________________________________ Libraries mailing list [hidden email] http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries