<div><div dir="auto">Hey Dominic ,</div></div><div dir="auto"><br></div><div dir="auto">There’s still a huge pile of release engineering I’ll do on top of the pull request change set, but I genuinely appreciate these patches!</div><div dir="auto"><br></div><div dir="auto">Thanks again! </div><div dir="auto">-Carter </div><div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, May 26, 2020 at 6:00 AM <<a href="mailto:dominic@steinitz.org">dominic@steinitz.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word;line-break:after-white-space"><p>Hello Libraries,</p><p>You may recall that following the blog <a href="https://alexey.kuleshevi.ch/blog/2019/12/21/random-benchmarks/" target="_blank">post</a> by @lehins, a group of us
(@curiousleo, @lehins and me) invited participation in <a href="https://mail.haskell.org/pipermail/libraries/2020-February/030261.html" target="_blank">February</a> to
take this work and apply it to improving the current <code>random</code> library.</p><p>Our proximate goals were to fix <a href="https://github.com/haskell/random/issues/25" target="_blank">#25</a> (filed in 2015) and <a href="https://github.com/haskell/random/issues/51" target="_blank">#51</a> (filed in
2018). After a lot of discussion and experimentation, we have a
proposal that addresses both these issues and also: <a href="https://github.com/haskell/random/issues/26" target="_blank">#26</a>, <a href="https://github.com/haskell/random/issues/44" target="_blank">#44</a>, <a href="https://github.com/haskell/random/issues/53" target="_blank">#53</a>,
<a href="https://github.com/haskell/random/issues/55" target="_blank">#55</a>, <a href="https://github.com/haskell/random/issues/58" target="_blank">#58</a> and <a href="https://github.com/haskell/random/issues/59" target="_blank">#59</a>.</p><p>For backwards compatibility, the proposal retains the old style
classes and enhances them. Thus in 1.1 we have</p>
<pre><code>class RandomGen g where
next :: g -> (Int, g)
genRange :: g -> (Int, Int)
split :: g -> (g, g)
{-# MINIMAL next, split #-}
</code></pre><p>and in 1.2 we have</p>
<pre><code>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) #-}
</code></pre><p>and <code>next</code> and <code>genRange</code> are deprecated. This interface is what
allows the significantly faster performance as no longer is everything
forced to go via <code>Integer</code>.</p><p>Several new interfaces are introduced and it is recommended that new
applications use these and, where feasible, existing applications
migrate to using them.</p><p>The major API addition in this PR is the definition of a new class <code>MonadRandom</code>:</p>
<pre><code>-- | '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
</code></pre><p>Conceptually, in <code>MonadRandom g s m</code>, <code>g s</code> is the type of the
generator, <code>s</code> is the state type, and <code>m</code> the underlying monad. Via
the functional dependency <code>g m -> s</code>, the state type is determined by
the generator and monad.</p><p><code>Frozen</code> is the type of the generator's state "at rest". It is defined
as an injective type family via <code>f -> g</code>, so there is no ambiguity as
to which <code>g</code> any <code>Frozen g</code> belongs to.</p><p>This definition is generic enough to accommodate, for example, the
<code>Gen</code> type from <code>mwc-random</code>, 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 <code>random</code> as <code>random</code> does not depend on <code>mwc-random</code>):</p>
<pre><code>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))
</code></pre><p>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 <code>StdGen</code> is
provided.</p><p>The <code>Random</code> typeclass has conceptually been split into <code>Uniform</code> and
<code>UniformRange</code>. The <code>Random</code> typeclass is still included for backwards
compatibility. <code>Uniform</code> is for types where it is possible to sample
from the type's entire domain; <code>UniformRange</code> is for types where one
can sample from a specified range:</p>
<pre><code>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
</code></pre><p>The proposal is a breaking change but the changes are not very
intrusive and we have PRs ready for the affected downstream libraries:</p>
<ul>
<li>requires <code>base</code> >= 4.10 (GHC-8.2)</li>
<li><code>StdGen</code> is no longer an instance of <code>Read</code></li>
<li><code>randomIO</code> and <code>randomRIO</code> were extracted from the <code>Random</code> class
into separate functions</li>
</ul><p>In addition, there may be import clashes with new functions,
e.g. <code>uniform</code> and <code>uniformR</code>.</p><p>Further explanatory details may be found
<a href="https://github.com/idontgetoutmuch/random/blob/v1.2-release-notes/RELEASE-NOTES-v1.2.md#api-changes" target="_blank">here</a>
and the PR for the proposed new version is
<a href="https://github.com/haskell/random/pull/61" target="_blank">here</a>.</p><p>Here are some benchmarks run on a 3.1 GHz Intel Core i7. The full
benchmarks can be run using e.g. <code>stack bench</code>. 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.</p>
<pre><code>| 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|
</code></pre><br><br><div>
<div dir="auto" style="word-wrap:break-word;line-break:after-white-space"><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">Dominic Steinitz</div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><a href="mailto:dominic@steinitz.org" target="_blank">dominic@steinitz.org</a></div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><a href="http://idontgetoutmuch.org" target="_blank">http://idontgetoutmuch.org</a></div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">Twitter: @idontgetoutmuch</div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br></div><br></div><br>
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