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copied!<p>So:</p> <pre><code>repeat :: a -> [a] randomIO :: Random a => IO a sequence :: Monad m => [m a] -> m [a] </code></pre> <p>=></p> <pre><code>repeat (randomIO :: IO Float) :: [IO Float] </code></pre> <p>So when you do:</p> <pre><code>random <- repeat (randomIO :: IO Float) </code></pre> <p>You're actually exploiting the list monad here, so <code>random</code> has type <code>IO Float</code>. Since you're in the list monad, your last statement needs to have type <code>[a]</code>, but it has type <code>IO ()</code> since it's a call to <code>print</code>, hence the type error.</p> <p>The whole point of sequence is to transform this <code>[IO a]</code> into an <code>IO [a]</code> that you can perform to obtain a list of random values, and hopefully print this list. Now, when you perform an IO like this, it needs to be performed all at once, unless using <code>unsafeInterleaveIO</code>, which is not recommended in this case. So it tries to get that infinite list... and hangs (it might stack overflow at some point, I'm not sure).</p> <p>To get an infinite list of random values, you don't need all this, just to obtain a random seed, and compute random values purely from the seed.</p> <p>You should be able to construct an infinite list of random values using these <a href="http://hackage.haskell.org/packages/archive/random/latest/doc/html/System-Random.html#t%3aRandom" rel="nofollow">functions</a>:</p> <pre><code>randomIO :: Random a => IO a -- to provide an IO Int mkStdGen :: Int -> StdGen -- to obtain a random generator from that Int randoms :: RandomGen g => g -> [a] -- to generate the infinite list </code></pre> <p>Notice that the last two functions are pure. Reading <a href="http://www.haskell.org/pipermail/haskell-cafe/2007-July/thread.html#29706" rel="nofollow">this thread</a> might give you some more ideas.</p> <hr> <p>EDIT:</p> <p>Example of how you should use <code>mkStdGen</code>:</p> <pre><code>randomList :: Random a => IO [a] randomList = do seed <- randomIO let gen = mkStdGen seed return (randoms gen) </code></pre> <p>I can't test it right now but this should work. You probably want to adapt this to your use case though.</p> <p>For your other question:</p> <pre><code>map :: (a -> b) -> [a] -> [b] print :: Show a => a -> IO () </code></pre> <p>=> map print :: Show a => [a] -> [IO ()]</p> <p>This probably isn't what you want, right? If you just want to print a list, no need for <code>map</code>, <code>print</code> can handle lists.</p>

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