title: OCaml: trying to count frequency of char in a string
body: <pre><code>let countA =0 in
  let countC =0 in
  let countG =0 in
  let countT =0 in
  let countChar x =
    match x with 
    'A' -&gt; countA = countA + 1
    |'C'-&gt; countC = countC + 1
    |'G' -&gt; countG = countG + 1
    |'T'-&gt; countT = countT + 1
  ;;
  </code></pre>
  
  <p>I am getting a syntax error but I don't understand why, i'm still pretty new to Ocaml.</p>