This tool lets you use some language elements, which are missing from GSC. For this, you have to work in a source folder, and the program will transform the code to proper GSC in another directory. It's also very good for compressing your scripts as much as possible.
Futher information, tutorial and a built version can be downloaded here: http://www.moddb.com/tutorials/pregsc
https://github.com/tronkko/dirent/blob/master/include/dirent.h