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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Control.Monad.Random</title><link href="ocean.css" rel="stylesheet" type="text/css" title="Ocean" /><script src="haddock-util.js" type="text/javascript"></script><script type="text/javascript">//<![CDATA[
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</script></head><body><div id="package-header"><ul class="links" id="page-menu"><li><a href="src/Control-Monad-Random.html">Source</a></li><li><a href="index.html">Contents</a></li><li><a href="doc-index.html">Index</a></li></ul><p class="caption">MonadRandom-0.1.13: Random-number generation monad.</p></div><div id="content"><div id="module-header"><table class="info"><tr><th>Portability</th><td>non-portable (multi-parameter type classes, undecidable instances)</td></tr><tr><th>Stability</th><td>experimental</td></tr><tr><th>Safe Haskell</th><td>None</td></tr></table><p class="caption">Control.Monad.Random</p></div><div id="table-of-contents"><p class="caption">Contents</p><ul><li><a href="#g:1">Special lift functions
</a></li><li><a href="#g:2">Example
</a></li></ul></div><div id="description"><p class="caption">Description</p><div class="doc"><p>A random number generation monad. See
<a href="http://www.haskell.org/haskellwiki/NewMonads/MonadRandom">http://www.haskell.org/haskellwiki/NewMonads/MonadRandom</a> for the original
version of this code.
</p><p>The actual interface is defined by
<code><a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a></code>.
</p><dl><dt>Computation type:</dt><dd> Computations which consume random values.
</dd><dt>Binding strategy:</dt><dd> The computation proceeds in the same fashion as the
identity monad, but it carries a random number generator that may be
queried to generate random values.
</dd><dt>Useful for:</dt><dd> Monte Carlo algorithms and simulating random processes.
</dd></dl></div></div><div id="synopsis"><p id="control.syn" class="caption expander" onclick="toggleSection('syn')">Synopsis</p><ul id="section.syn" class="hide" onclick="toggleSection('syn')"><li class="src short">module <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html">System.Random</a></li><li class="src short">module <a href="Control-Monad-Random-Class.html">Control.Monad.Random.Class</a></li><li class="src short"><a href="#v:evalRandT">evalRandT</a> :: (<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="Control-Monad-Random.html#t:RandT">RandT</a> g m a -> g -> m a</li><li class="src short"><a href="#v:runRandT">runRandT</a> :: (<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="Control-Monad-Random.html#t:RandT">RandT</a> g m a -> g -> m (a, g)</li><li class="src short"><a href="#v:evalRand">evalRand</a> :: <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g => <a href="Control-Monad-Random.html#t:Rand">Rand</a> g a -> g -> a</li><li class="src short"><a href="#v:runRand">runRand</a> :: <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g => <a href="Control-Monad-Random.html#t:Rand">Rand</a> g a -> g -> (a, g)</li><li class="src short"><a href="#v:evalRandIO">evalRandIO</a> :: <a href="Control-Monad-Random.html#t:Rand">Rand</a> <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:StdGen">StdGen</a> a -> <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/System-IO.html#t:IO">IO</a> a</li><li class="src short"><a href="#v:fromList">fromList</a> :: <a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a> m => [(a, <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Prelude.html#t:Rational">Rational</a>)] -> m a</li><li class="src short"><a href="#v:uniform">uniform</a> :: <a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a> m => [a] -> m a</li><li class="src short"><span class="keyword">data</span> <a href="#t:Rand">Rand</a> g a</li><li class="src short"><span class="keyword">data</span> <a href="#t:RandT">RandT</a> g m a</li><li class="src short"><a href="#v:liftRand">liftRand</a> :: (<a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:Random">Random</a> a) => (g -> (a, g)) -> <a href="Control-Monad-Random.html#t:Rand">Rand</a> g a</li><li class="src short"><a href="#v:liftRandT">liftRandT</a> :: (<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:Random">Random</a> a) => (g -> m (a, g)) -> <a href="Control-Monad-Random.html#t:RandT">RandT</a> g m a</li></ul></div><div id="interface"><h1>Documentation</h1><div class="top"><p class="src">module <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html">System.Random</a></p></div><div class="top"><p class="src">module <a href="Control-Monad-Random-Class.html">Control.Monad.Random.Class</a></p></div><div class="top"><p class="src"><a name="v:evalRandT" class="def">evalRandT</a> :: (<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="Control-Monad-Random.html#t:RandT">RandT</a> g m a -> g -> m a<a href="src/Control-Monad-Random.html#evalRandT" class="link">Source</a></p><div class="doc"><p>Evaluate a RandT computation using the generator <code>g</code>. Note that the
generator <code>g</code> is not returned, so there's no way to recover the
updated version of <code>g</code>.
</p></div></div><div class="top"><p class="src"><a name="v:runRandT" class="def">runRandT</a> :: (<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="Control-Monad-Random.html#t:RandT">RandT</a> g m a -> g -> m (a, g)<a href="src/Control-Monad-Random.html#runRandT" class="link">Source</a></p><div class="doc"><p>Run a RandT computation using the generator <code>g</code>, returning the result and
the updated generator.
</p></div></div><div class="top"><p class="src"><a name="v:evalRand" class="def">evalRand</a> :: <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g => <a href="Control-Monad-Random.html#t:Rand">Rand</a> g a -> g -> a<a href="src/Control-Monad-Random.html#evalRand" class="link">Source</a></p><div class="doc"><p>Evaluate a random computation using the generator <code>g</code>. Note that the
generator <code>g</code> is not returned, so there's no way to recover the
updated version of <code>g</code>.
</p></div></div><div class="top"><p class="src"><a name="v:runRand" class="def">runRand</a> :: <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g => <a href="Control-Monad-Random.html#t:Rand">Rand</a> g a -> g -> (a, g)<a href="src/Control-Monad-Random.html#runRand" class="link">Source</a></p><div class="doc"><p>Run a random computation using the generator <code>g</code>, returning the result
and the updated generator.
</p></div></div><div class="top"><p class="src"><a name="v:evalRandIO" class="def">evalRandIO</a> :: <a href="Control-Monad-Random.html#t:Rand">Rand</a> <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:StdGen">StdGen</a> a -> <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/System-IO.html#t:IO">IO</a> a<a href="src/Control-Monad-Random.html#evalRandIO" class="link">Source</a></p><div class="doc"><p>Evaluate a random computation in the IO monad, splitting the global standard generator to get a new one for the computation.
</p></div></div><div class="top"><p class="src"><a name="v:fromList" class="def">fromList</a> :: <a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a> m => [(a, <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Prelude.html#t:Rational">Rational</a>)] -> m a<a href="src/Control-Monad-Random.html#fromList" class="link">Source</a></p><div class="doc"><p>Sample a random value from a weighted list. The total weight of all
elements must not be 0.
</p></div></div><div class="top"><p class="src"><a name="v:uniform" class="def">uniform</a> :: <a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a> m => [a] -> m a<a href="src/Control-Monad-Random.html#uniform" class="link">Source</a></p><div class="doc"><p>Sample a value from a uniform distribution of a list of elements.
</p></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a name="t:Rand" class="def">Rand</a> g a <a href="src/Control-Monad-Random.html#Rand" class="link">Source</a></p><div class="doc"><p>A basic random monad.
</p></div><div class="subs instances"><p id="control.i:Rand" class="caption collapser" onclick="toggleSection('i:Rand')">Instances</p><div id="section.i:Rand" class="show"><table><tr><td class="src"><a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g => <a href="Control-Monad-Random-Class.html#t:MonadSplit">MonadSplit</a> g (<a href="Control-Monad-Random.html#t:Rand">Rand</a> g)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> (<a href="Control-Monad-Random.html#t:Rand">Rand</a> g)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Functor">Functor</a> (<a href="Control-Monad-Random.html#t:Rand">Rand</a> g)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad-Fix.html#t:MonadFix">MonadFix</a> (<a href="Control-Monad-Random.html#t:Rand">Rand</a> g)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Applicative.html#t:Applicative">Applicative</a> (<a href="Control-Monad-Random.html#t:Rand">Rand</a> g)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g => <a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a> (<a href="Control-Monad-Random.html#t:Rand">Rand</a> g)</td><td class="doc empty"> </td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a name="t:RandT" class="def">RandT</a> g m a <a href="src/Control-Monad-Random.html#RandT" class="link">Source</a></p><div class="doc"><p>A monad transformer which adds a random number generator to an
existing monad.
</p></div><div class="subs instances"><p id="control.i:RandT" class="caption collapser" onclick="toggleSection('i:RandT')">Instances</p><div id="section.i:RandT" class="show"><table><tr><td class="src"><a href="/usr/share/doc/libghc-mtl-doc/html/Control-Monad-Reader-Class.html#t:MonadReader">MonadReader</a> r m => <a href="/usr/share/doc/libghc-mtl-doc/html/Control-Monad-Reader-Class.html#t:MonadReader">MonadReader</a> r (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src">(<a href="/usr/share/doc/libghc-mtl-doc/html/Control-Monad-State-Class.html#t:MonadState">MonadState</a> s m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="/usr/share/doc/libghc-mtl-doc/html/Control-Monad-State-Class.html#t:MonadState">MonadState</a> s (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/libghc-mtl-doc/html/Control-Monad-Writer-Class.html#t:MonadWriter">MonadWriter</a> w m => <a href="/usr/share/doc/libghc-mtl-doc/html/Control-Monad-Writer-Class.html#t:MonadWriter">MonadWriter</a> w (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src">(<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="Control-Monad-Random-Class.html#t:MonadSplit">MonadSplit</a> g (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src">MonadTrans (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m => <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Functor">Functor</a> m => <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Functor">Functor</a> (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad-Fix.html#t:MonadFix">MonadFix</a> m => <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad-Fix.html#t:MonadFix">MonadFix</a> (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src">(<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Functor">Functor</a> m, <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m) => <a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Applicative.html#t:Applicative">Applicative</a> (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src">MonadIO m => MonadIO (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr><tr><td class="src">(<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g) => <a href="Control-Monad-Random-Class.html#t:MonadRandom">MonadRandom</a> (<a href="Control-Monad-Random.html#t:RandT">RandT</a> g m)</td><td class="doc empty"> </td></tr></table></div></div></div><h1 id="g:1">Special lift functions
</h1><div class="top"><p class="src"><a name="v:liftRand" class="def">liftRand</a><a href="src/Control-Monad-Random.html#liftRand" class="link">Source</a></p><div class="subs arguments"><p class="caption">Arguments</p><table><tr><td class="src">:: (<a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:Random">Random</a> a)</td><td class="doc empty"> </td></tr><tr><td class="src">=> (g -> (a, g))</td><td class="doc"><p>action returning value and new generator state
</p></td></tr><tr><td class="src">-> <a href="Control-Monad-Random.html#t:Rand">Rand</a> g a</td><td class="doc empty"> </td></tr></table></div><div class="doc"><p>Lift arbitrary action to Rand
</p></div></div><div class="top"><p class="src"><a name="v:liftRandT" class="def">liftRandT</a><a href="src/Control-Monad-Random.html#liftRandT" class="link">Source</a></p><div class="subs arguments"><p class="caption">Arguments</p><table><tr><td class="src">:: (<a href="/usr/share/doc/ghc-doc/html/libraries/base-4.6.0.1/Control-Monad.html#t:Monad">Monad</a> m, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:RandomGen">RandomGen</a> g, <a href="/usr/share/doc/libghc-random-doc/html/System-Random.html#t:Random">Random</a> a)</td><td class="doc empty"> </td></tr><tr><td class="src">=> (g -> m (a, g))</td><td class="doc"><p>action returning value and new generator state
</p></td></tr><tr><td class="src">-> <a href="Control-Monad-Random.html#t:RandT">RandT</a> g m a</td><td class="doc empty"> </td></tr></table></div><div class="doc"><p>Lift arbitrary action to RandT
</p></div></div><h1 id="g:2">Example
</h1><div class="doc"><p>The <code>die</code> function simulates the roll of a die, picking a number between 1
and 6, inclusive, and returning it in the <code><a href="Control-Monad-Random.html#t:Rand">Rand</a></code> monad. Notice that this
code will work with any source of random numbers <code>g</code>.
</p><pre>die :: (RandomGen g) => Rand g Int
die = getRandomR (1,6)
</pre><p>The <code>dice</code> function uses <code>replicate</code> and <code>sequence</code> to simulate the roll of
<code>n</code> dice.
</p><pre>dice :: (RandomGen g) => Int -> Rand g [Int]
dice n = sequence (replicate n die)
</pre><p>To extract a value from the <code><a href="Control-Monad-Random.html#t:Rand">Rand</a></code> monad, we can can use <code><a href="Control-Monad-Random.html#v:evalRandIO">evalRandIO</a></code>.
</p><pre>main = do
values <- evalRandIO (dice 2)
putStrLn (show values)
</pre></div></div></div><div id="footer"><p>Produced by <a href="http://www.haskell.org/haddock/">Haddock</a> version 2.13.2</p></div></body></html>
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