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copied!<p>(<strong>Note:</strong> ehird's answer makes a very good point regarding a race condition. It should be kept in mind when reading my answer, which ignores the issue. Do note also that the imperative pseudo-code presented in the question also suffers from the same problem.)</p> <p>What defines the filename? Is it given in the program, or supplied by the user? In your imperative pseudo-code, it's a constant string in the program. I'll assume you want the user to supply it by passing it as the first command line argument to the program.</p> <p>Then I suggest something like this:</p> <pre><code>import Control.Monad import System.Directory import System.Environment doSomethingElse :: IO () main = do args <- getArgs fileExists <- doesFileExist (head args) when fileExists (removeFile (head args)) doSomethingElse </code></pre> <p>(As you can see, I added the type signature of <code>doSomethingElse</code> to avoid confusion).</p> <p>I import <code>System.Environment</code> for the <code>getArgs</code> function. In case the file in question is simply given by a constant string (such as in your imperative pseudo-code), just remove all the args stuff and fill in the constant string wherever I have <code>head args</code>.</p> <p><code>Control.Monad</code> is imported to get the <code>when</code> function. Note that this useful function is <em>not</em> a keyword (like <code>if</code>), but an ordinary function. Let's look at its type:</p> <pre><code>when :: Monad m => Bool -> m () -> m () </code></pre> <p>In your case <code>m</code> is <code>IO</code>, so you can think of <code>when</code> as a function that takes a <code>Bool</code> and an IO action and performs the action only if the <code>Bool</code> is <code>True</code>. Of course you could solve your problem with <code>if</code>s, but in your case <code>when</code> reads a lot clearer. At least I think so.</p> <p><strong>Addendum:</strong> If you, like I did at first, get the feeling that <code>when</code> is some magical and difficult machinery, it's very instructive to try to define the function yourself. I promise you, it's dead simple...</p>

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