Improving Random
David Feuer
david.feuer at gmail.com
Tue May 26 20:53:00 UTC 2020
Could you explain the reasoning behind the deprecations?
On Tue, May 26, 2020, 6:00 AM <dominic at steinitz.org> wrote:
> Hello Libraries,
>
> You may recall that following the blog post
> <https://alexey.kuleshevi.ch/blog/2019/12/21/random-benchmarks/> by
> @lehins, a group of us (@curiousleo, @lehins and me) invited participation
> in February
> <https://mail.haskell.org/pipermail/libraries/2020-February/030261.html>
> to take this work and apply it to improving the current random library.
>
> Our proximate goals were to fix #25
> <https://github.com/haskell/random/issues/25> (filed in 2015) and #51
> <https://github.com/haskell/random/issues/51> (filed in 2018). After a
> lot of discussion and experimentation, we have a proposal that addresses
> both these issues and also: #26
> <https://github.com/haskell/random/issues/26>, #44
> <https://github.com/haskell/random/issues/44>, #53
> <https://github.com/haskell/random/issues/53>, #55
> <https://github.com/haskell/random/issues/55>, #58
> <https://github.com/haskell/random/issues/58> and #59
> <https://github.com/haskell/random/issues/59>.
>
> For backwards compatibility, the proposal retains the old style classes
> and enhances them. Thus in 1.1 we have
>
> class RandomGen g where
> next :: g -> (Int, g)
> genRange :: g -> (Int, Int)
> split :: g -> (g, g)
> {-# MINIMAL next, split #-}
>
> and in 1.2 we have
>
> class RandomGen g where
> next :: g -> (Int, g)
> genWord8 :: g -> (Word8, g)
> genWord16 :: g -> (Word16, g)
> genWord32 :: g -> (Word32, g)
> genWord64 :: g -> (Word64, g)
> genWord32R :: Word32 -> g -> (Word32, g)
> genWord64R :: Word64 -> g -> (Word64, g)
> genShortByteString :: Int
> -> g -> (Data.ByteString.Short.Internal.ShortByteString, g)
> genRange :: g -> (Int, Int)
> split :: g -> (g, g)
> {-# MINIMAL split, (genWord32 | genWord64 | next, genRange) #-}
>
> and next and genRange are deprecated. This interface is what allows the
> significantly faster performance as no longer is everything forced to go
> via Integer.
>
> Several new interfaces are introduced and it is recommended that new
> applications use these and, where feasible, existing applications migrate
> to using them.
>
> The major API addition in this PR is the definition of a new class
> MonadRandom:
>
> -- | 'MonadRandom' is an interface to monadic pseudo-random number generators.
> class Monad m => MonadRandom g s m | g m -> s where
> {-# MINIMAL freezeGen,thawGen,(uniformWord32|uniformWord64) #-}
>
> type Frozen g = (f :: Type) | f -> g
> freezeGen :: g s -> m (Frozen g)
> thawGen :: Frozen g -> m (g s)
>
> uniformWord32 :: g s -> m Word32 -- default implementation in terms of uniformWord64
> uniformWord64 :: g s -> m Word64 -- default implementation in terms of uniformWord32
> -- plus methods for other word sizes and for byte strings
> -- all have default implementations so the MINIMAL pragma holds
>
> Conceptually, in MonadRandom g s m, g s is the type of the generator, s
> is the state type, and m the underlying monad. Via the functional
> dependency g m -> s, the state type is determined by the generator and
> monad.
>
> Frozen is the type of the generator's state "at rest". It is defined as
> an injective type family via f -> g, so there is no ambiguity as to which
> g any Frozen g belongs to.
>
> This definition is generic enough to accommodate, for example, the Gen
> type from mwc-random, which itself abstracts over the underlying
> primitive monad and state token. This is the full instance declaration
> (provided here as an example - this instance is not part of random as
> random does not depend on mwc-random):
>
> instance (s ~ PrimState m, PrimMonad m) => MonadRandom MWC.Gen s m where
> type Frozen MWC.Gen = MWC.Seed
> freezeGen = MWC.save
> thawGen = MWC.restore
>
> uniformWord8 = MWC.uniform
> uniformWord16 = MWC.uniform
> uniformWord32 = MWC.uniform
> uniformWord64 = MWC.uniform
> uniformShortByteString n g = unsafeSTToPrim (genShortByteStringST n (MWC.uniform g))
>
> Pure random number generators can also be made instances of this class
> providing a uniform interface to both pure and stateful random number
> generators. An instance for the standard number generator StdGen is
> provided.
>
> The Random typeclass has conceptually been split into Uniform and
> UniformRange. The Random typeclass is still included for backwards
> compatibility. Uniform is for types where it is possible to sample from
> the type's entire domain; UniformRange is for types where one can sample
> from a specified range:
>
> class Uniform a where
> uniformM :: MonadRandom g s m => g s -> m a
>
> class UniformRange a where
> uniformRM :: MonadRandom g s m => (a, a) -> g s -> m a
>
> The proposal is a breaking change but the changes are not very intrusive
> and we have PRs ready for the affected downstream libraries:
>
> - requires base >= 4.10 (GHC-8.2)
> - StdGen is no longer an instance of Read
> - randomIO and randomRIO were extracted from the Random class into
> separate functions
>
> In addition, there may be import clashes with new functions, e.g. uniform
> and uniformR.
>
> Further explanatory details may be found here
> <https://github.com/idontgetoutmuch/random/blob/v1.2-release-notes/RELEASE-NOTES-v1.2.md#api-changes>
> and the PR for the proposed new version is here
> <https://github.com/haskell/random/pull/61>.
>
> Here are some benchmarks run on a 3.1 GHz Intel Core i7. The full
> benchmarks can be run using e.g. stack bench. The benchmarks are measured
> in milliseconds per 100,000 generations. In some cases, the performance is
> over x1000(!) times better; the minimum performance increase for the types
> listed below is more than x35.
>
> | Name | Mean (1.1) | Mean (1.2) | Improvement|
> | ----------------------- | ---------- | ---------- | ---------- |
> | pure/random/Float | 30 | 0.03 | 1038|
> | pure/random/Double | 52 | 0.03 | 1672|
> | pure/random/Integer | 43 | 0.33 | 131|
> | pure/uniform/Word8 | 14 | 0.03 | 422|
> | pure/uniform/Word16 | 13 | 0.03 | 375|
> | pure/uniform/Word32 | 21 | 0.03 | 594|
> | pure/uniform/Word64 | 42 | 0.03 | 1283|
> | pure/uniform/Word | 44 | 0.03 | 1491|
> | pure/uniform/Int8 | 15 | 0.03 | 511|
> | pure/uniform/Int16 | 15 | 0.03 | 507|
> | pure/uniform/Int32 | 22 | 0.03 | 749|
> | pure/uniform/Int64 | 44 | 0.03 | 1405|
> | pure/uniform/Int | 43 | 0.03 | 1512|
> | pure/uniform/Char | 17 | 0.49 | 35|
> | pure/uniform/Bool | 18 | 0.03 | 618|
> | pure/uniform/CChar | 14 | 0.03 | 485|
> | pure/uniform/CSChar | 14 | 0.03 | 455|
> | pure/uniform/CUChar | 13 | 0.03 | 448|
> | pure/uniform/CShort | 14 | 0.03 | 473|
> | pure/uniform/CUShort | 13 | 0.03 | 457|
> | pure/uniform/CInt | 21 | 0.03 | 737|
> | pure/uniform/CUInt | 21 | 0.03 | 742|
> | pure/uniform/CLong | 43 | 0.03 | 1544|
> | pure/uniform/CULong | 42 | 0.03 | 1460|
> | pure/uniform/CPtrdiff | 43 | 0.03 | 1494|
> | pure/uniform/CSize | 43 | 0.03 | 1475|
> | pure/uniform/CWchar | 22 | 0.03 | 785|
> | pure/uniform/CSigAtomic | 21 | 0.03 | 749|
> | pure/uniform/CLLong | 43 | 0.03 | 1554|
> | pure/uniform/CULLong | 42 | 0.03 | 1505|
> | pure/uniform/CIntPtr | 43 | 0.03 | 1476|
> | pure/uniform/CUIntPtr | 42 | 0.03 | 1463|
> | pure/uniform/CIntMax | 43 | 0.03 | 1535|
> | pure/uniform/CUIntMax | 42 | 0.03 | 1493|
>
>
>
> Dominic Steinitz
> dominic at steinitz.org
> http://idontgetoutmuch.org
> Twitter: @idontgetoutmuch
>
>
>
>
> _______________________________________________
> Libraries mailing list
> Libraries at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/libraries/attachments/20200526/821dd481/attachment.html>
More information about the Libraries
mailing list