title: How to convert the column name to its column index in Haskell
body: <p>Excel column names are like A, B, C ... AA, AB, AC up to infinite. How can i convert the column name to its column index in Haskell. I can convert index to column but couldnt make the reverse function. Can someone explain me how to write the reverse function of it ? Index to column:</p>
  
  <pre><code>f n = (concatMap sequence $ tail $ iterate (['A'..'Z'] :) []) !! n
  </code></pre>