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    <p><code>return</code> in haskell does not do the same thing as <code>return</code> in other languages. Instead, what <code>return</code> does is to inject a value into a monad (in this case <code>IO</code>). You have a couple of options</p> <p>the most simple is to use if</p> <pre><code>scrapePage :: String -&gt; IO () scrapePage url = do doc &lt;- fromUrl url title &lt;- liftM headMay $ runX $ doc &gt;&gt;&gt; css "head.title" &gt;&gt;&gt; getText if (isNothing title) then return () else do date &lt;- liftM headMay $ runX $ doc &gt;&gt;&gt; css "span.dateTime" ! "data-utc" if (isNothing date) then return () else do -- etc -- make page object and send it to db return () </code></pre> <p>another option is to use <code>unless</code></p> <pre><code>scrapePage url = do doc &lt;- fromUrl url title &lt;- liftM headMay $ runX $ doc &gt;&gt;&gt; css "head.title" &gt;&gt;&gt; getText unless (isNothing title) do date &lt;- liftM headMay $ runX $ doc &gt;&gt;&gt; css "span.dateTime" ! "data-utc" unless (isNothing date) do -- etc -- make page object and send it to db return () </code></pre> <p>the general problem here is that the <code>IO</code> monad doesn't have control effects (except for exceptions). On the other hand, you could use the maybe monad transformer</p> <pre><code>scrapePage url = liftM (maybe () id) . runMaybeT $ do doc &lt;- liftIO $ fromUrl url title &lt;- liftIO $ liftM headMay $ runX $ doc &gt;&gt;&gt; css "head.title" &gt;&gt;&gt; getText guard (isJust title) date &lt;- liftIO $ liftM headMay $ runX $ doc &gt;&gt;&gt; css "span.dateTime" ! "data-utc" guard (isJust date) -- etc -- make page object and send it to db return () </code></pre> <p>if you really want to get full blown control effects you need to use <code>ContT</code></p> <pre><code>scrapePage :: String -&gt; IO () scrapePage url = runContT return $ do doc &lt;- fromUrl url title &lt;- liftM headMay $ runX $ doc &gt;&gt;&gt; css "head.title" &gt;&gt;&gt; getText when (isNothing title) $ callCC ($ ()) date &lt;- liftM headMay $ runX $ doc &gt;&gt;&gt; css "span.dateTime" ! "data-utc" when (isNothing date) $ callCC ($ ()) -- etc -- make page object and send it to db return () </code></pre> <p>WARNING: none of the above code has been tested, or even type checked!</p>
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