Our team maintains project that has been written few years ago on C++. The project is not so vast, but consists of few modules. One module ensures parsing and interpretation from language that is very similar to Excel, but it's needed for another goals. So, we are considering another concept for parsing by using on syntax analyze by means of grammars.
Flex and Bison is that tool that exactly fits to this goal. It's simple, understandable for other developers and, finally, implements parses that I need.
But there is one problem: I couldn't find an another tool that solve the same task. Flex and Bison are GNU. I found dubios solutions for integrating it in Visual Studio with using some fixed execution files to Windows but I don't trust to this way. Is it safe to use this way to huge workable project, because no one guarantees that flex and Bison will be maintained in next version of Windows. How to make right decision?
Flex and bison are written in portable C, and the code they generate is portable C. There is little likelihood that they will not work with future versions of Windows/Visual Studio.
Bison is Gnu but Flex is not; Flex is distributed under a slightly modified BSD license which places very few restrictions on its use. There are also other than yacc-like utilities which could be used in place of bison, although I don't believe the Gnu license has been problematic.
In short, I wouldn't worry about it. But it's your project.