I'm writing a jFlex lexer for Lua, and I'm having problems designing a regular expression to match one particular part of the language specification:
Literal strings can also be defined using a long format enclosed by long brackets. We define an opening long bracket of level n as an opening square bracket followed by n equal signs followed by another opening square bracket. So, an opening long bracket of level 0 is written as [[, an opening long bracket of level 1 is written as [=[, and so on. A closing long bracket is defined similarly; for instance, a closing long bracket of level 4 is written as ]====]. A long string starts with an opening long bracket of any level and ends at the first closing long bracket of the same level. Literals in this bracketed form can run for several lines, do not interpret any escape sequences, and ignore long brackets of any other level. They can contain anything except a closing bracket of the proper level.
In a nutshell, I am trying to design a regular expression that will match an opening long bracket, the string contents in between, and the closing long bracket. A match should only occur when the opening long bracket and closing long bracket have the same number of equal signs, which can be zero or more.