title: Haskell from integer into a string (own function)
body: <p>I need help with my function to convert an integer into a string:</p>
  <p>for example: fromInteger 19 == &quot;91&quot;</p>
  <p>My auxiliary-function to convert an integer into a character:</p>
  <pre><code>fromDigit :: Integer -&gt; Char
  fromDigit 0 = '0'
  fromDigit 1 = '1'
  fromDigit 2 = '2'
  fromDigit 3 = '3'
  fromDigit 4 = '4'
  fromDigit 5 = '5' 
  fromDigit 6 = '6'
  fromDigit 7 = '7'
  fromDigit 8 = '8'
  fromDigit 9 = '9'
  </code></pre>
  <p>This is my main function:</p>
  <pre><code>fromInteger :: Integer -&gt; String
  fromInteger n = 
  if n == 0 then &quot;&quot;
  else fromInteger(tail n) ++ fromDigit(head n)
  </code></pre>
  <p>I should only use: tail, head, :, null and mathematical functions</p>