Regex character match counter

This is impossible to do properly with (only) a regex. Since the [ and ] characters can be recursively nested, regular expressions cannot be used, since a regular expression does not have a stack to keep track of matching brackets. A good rule of the thumb is, if you have recursive patterns (patterns that can be nested inside themselves), you cannot use regular expressions.

The proper method would be to use a tokenizer using regular expressions and then create a recursive descent parser. Depending on your skill in writing parser code, this will set you back a few days of coding.

The improper but crudely effective way would be to recognise that the beginning of a function and the end of a function will both start at the same indentation level. You can create a special regex that does not match the recursive pattern, but simply matches anything between the start of your function definition and a closing brace that starts at the beginning of a line. This will probably take you an hour or two to write and debug.

I guess it is possible to do with regex, however without brackets counting (this is what regex engine cannot do). Reluctant quantifier may be used instead to match the first occurrence of method ending bracket (assuming it is always first/only char on the line, or -- END ... comment is always present).

In my opinion however regex is not appropriate tool for such a purpose, 'cause it can be very memory and time ineffective over long multi line and multi branch code.

Consider writing a simple parser instead.

Here's a quick example using pyparsing that strips comments such as "-- END OF METHOD"

from pyparsing import *

parser = nestedExpr('[', ']').setParseAction(keepOriginalText) + Group('--' + restOfLine).suppress()
print parser.transformString(text)

Produces with your example code:

fn difflml(args)[
       if [
            --blah 
           ]
       [ var ]
]

--Othed method starts and stuffs