I had a look at the repo in https://sourceforge.net/p/recoil/code/ci/master/tree/ - I think the meat of it is a giant file called 'recoil.fu' (22481 lines long)

[edit] it is written in the 'Fusion Language' https://github.com/fusionlanguage/fut (and not https://gaelduval.com/introducing-fusion-the-ultimate-progra... !) - there's a playground at http://fusion-lang.org/ . I'd never heard of it before but seems a bit like Haxe perhaps?