expression parsing

[Bing Ran]

Thanks so much for the project which has made my life a lot easier!

Quick questions: given a string such as "a + b c", what is the most
efficient way to find out the longest sub-string, from the start, that
is a valid expression, in this case "a + b"?

It seems to me the parser can only parse a full class definition
instead finer constructs.

Thanks

Bing