Memo.Lines question

Hi,
   I need to write a function which takes a line of a memo and checks each character as it goes. If it finds a character which is in a predefined subset, it should be returned. It's for an app which needs to check brackets. So if the subset of 'important' characters were '{ , }, [ ,] , ( , )' and the line in the memo was :

(information[this[ this and this]] {more gibberish}).

Then the function would put up a messagebox saying :

   '([[]]{})'
All brackets match;

I can write most of it, I just need to know how to inspect each character in the line. Anyone know how to do it?
Cheers, Nik.