title: Haskell: Multi-way if-expressions need MultiWayIf turned on
body: <p>Trying to build with "stack build":</p>
  
  <pre><code>module Main where
  
  
  analyzeGold :: Int -&gt; String
  analyzeGold standard =
    if | standard == 999 -&gt; "Wow! 999 standard!"
       | standard == 750 -&gt; "Great! 750 standard."
       | standard == 585 -&gt; "Not bad! 585 standard."
       | otherwise -&gt; "I don't know such a standard..."
  
  main :: IO ()
  main = do
    putStrLn (analyzeGold 999)
  </code></pre>
  
  <p>And I got: </p>
  
  <pre><code>    Multi-way if-expressions need MultiWayIf turned on
    |
  6 |   if | standard == 999 -&gt; "Wow! 999 standard!"
    |   ^^
  </code></pre>
  
  <p>How to fix it?</p>
  
  <p>stack 1.7.1, GHC 8.2.2</p>