title: Haskell calculator
body: <p>Here is my new main with the <code>error: parse error on input '-&gt;'</code>
  I commented where the error is. Could it be an indentation error somewhere? </p>
  
  <pre><code>main :: IO()
  main = do
    expression &lt;- evaluate_input
    putStrLn $ show $ compute expression
  
  evaluate_input :: IO ()
  evaluate_input = do
    args &lt;- getArgs
    case args of
      a:s -&gt; return a
      -&gt; do putStrLn "Enter Expression or 'end' to exit calculator"
             hFlush stdout
             getLine
             unless (expression -&gt; "end") $ showExpr expression --error here
    where
      showExpr expression = do putStrLn $ evaluateExpr expression
                          evaluate_input
  evaluateExpr :: String -&gt; String
  evaluateExpr = show
  </code></pre>