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POSystem.Random behaving very strangely; numbers displayed are not the numbers being operated on
 

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  1. POSystem.Random behaving very strangely; numbers displayed are not the numbers being operated on
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    <p>I needed to generate some random numbers for testing purposes. I have never used Data.Random before. I needed to do many tests and I would not know the amount of numbers I would need in advance, but I would know that they should fall into a certain bound. I wrote the function:</p> <pre><code>import System.Random f k = (\(x,y) -&gt; x*y &lt; (10^k) &amp;&amp; x*y &gt;0 ) rands n g k = take n $ filter (\(x,y) -&gt; x*y &lt; (10^k) &amp;&amp; x*y &gt;0 ) (zip a b) where a = randomRs (1::Int, 10^k-1) ga b = randomRs (1::Int, 10^k-1) gb (ga, gb) = split $ mkStdGen g </code></pre> <p>and began to test things using the numbers it generated. I began to notice strange things when using this function:</p> <pre><code>testRands n k = do g1 &lt;- randomIO g2 &lt;- randomIO let r = rands n (mkStdGen g1, mkStdGen g2) k putStrLn $ show r putStrLn $ show $ map (\(x,y) -&gt; x*y &lt; 10^k &amp;&amp; x*y &gt;0) r putStrLn $ show $ map (\(x,y) -&gt; x*y) r putStrLn $ show $ maximum $ map (\(x,y) -&gt; x*y) r *Main&gt; testRands 4 7 [(6193574,9385226),(9634973,5475375),(5070277,7408626),(3801396,5652588)] [True,True,True,True] [4353660,6993107,2038586,4030960] 6993107 </code></pre> <p>I then copy the numbers it generated and paste them back into GHCI and call the exact same predicate function on all of them:</p> <pre><code>*Main&gt; map (f 7) [(6193574,9385226),(9634973,5475375),(5070277,7408626),(3801396,5652588)] [False,False,False,False] </code></pre> <p>This makes no sense and I don't even know where to start trying to fix it.</p>
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