title: "Illegal view pattern: fromPathPiece -> Just dyn_abDD" when using parameters on routes
body: <p>I'm using yesod version 1.4.0 within a cabal sandbox.</p>
  
  <p>I have the following routes file:</p>
  
  <pre><code>/static StaticR Static getStatic
  /auth   AuthR   Auth   getAuth
  
  /favicon.ico FaviconR GET
  /robots.txt RobotsR GET
  
  / HomeR GET POST
  /config/#String MakeConfigR GET POST
  </code></pre>
  
  <p>and a matching (properly imported and everything) handler file for the implementation.</p>
  
  <p>However, whenever yesod (or when I manually) try to compile, I get the following error</p>
  
  <pre><code>Foundation.hs:48:1:
      Illegal view pattern:  fromPathPiece -&gt; Just dyn_abDD
      Use -XViewPatterns to enable view patterns
  </code></pre>
  
  <p>I haven't modified Foundation.hs in any way.</p>
  
  <p>When I only have a route that takes no parameters, such as</p>
  
  <pre><code>/noparamshere NoParamsR GET
  </code></pre>
  
  <p>or something similar in my routes file, everything works fine. What have I done wrong?</p>