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POGetting confused with MonadBaseControl errors while learning Conduits in Haskell
 

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  1. POGetting confused with MonadBaseControl errors while learning Conduits in Haskell
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    <p>I'm trying go learn about Conduits in Haskell. It sounds interesting, but the types are quickly getting extremely confusing. </p> <p>I've got the following file written so far: <a href="https://gist.github.com/anonymous/7991727" rel="nofollow">https://gist.github.com/anonymous/7991727</a></p> <p>Presumably, what it would do is that, given a series of ticker symbols, it would go to Yahoo Finance and download the associated data file. Sounds simple enough.</p> <p><code>getLink</code> and <code>extractLink</code> works great. No problems there.</p> <p><code>downloadContent</code> is giving me all sorts of compile problems. This source code:</p> <pre><code>downloadContent manager = do mx &lt;- await case mx of Nothing -&gt; return () Just (sym, Nothing) -&gt; return () Just (sym, Just link) -&gt; do req &lt;- parseUrl link res &lt;- http req manager responseBody res $$+- sinkFile sym </code></pre> <p>The exact error I'm getting is this:</p> <pre><code>src/suckyahoo.hs:58:21: No instance for (MonadBaseControl IO (ConduitM [Char] ([Char], Maybe String) (ResourceT (ResourceT IO)))) arising from a use of `getLink' Possible fix: add an instance declaration for (MonadBaseControl IO (ConduitM [Char] ([Char], Maybe String) (ResourceT (ResourceT IO)))) In the second argument of `($=)', namely `getLink manager' In the first argument of `($$)', namely `sourceSyms $= getLink manager' In a stmt of a 'do' block: sourceSyms $= getLink manager $$ downloadContent manager src/suckyahoo.hs:58:40: No instance for (MonadBaseControl IO (ConduitM (FilePath, Maybe String) void-0.6.1:Data.Void.Void (ResourceT (ResourceT IO)))) arising from a use of `downloadContent' Possible fix: add an instance declaration for (MonadBaseControl IO (ConduitM (FilePath, Maybe String) void-0.6.1:Data.Void.Void (ResourceT (ResourceT IO)))) In the second argument of `($$)', namely `downloadContent manager' In a stmt of a 'do' block: sourceSyms $= getLink manager $$ downloadContent manager In the expression: do { sourceSyms $= getLink manager $$ downloadContent manager } Failed, modules loaded: none. </code></pre> <p>What is the insight here that will let me accomplish the intent of the code?</p>
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    1. COIt this error for this code? I don't see "urlSource $= getLink manager $$ downloadContent manager" anywhere in the code snippet?
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