I'll let you decide whether it counts as "mainstream", but the principal implementation of Nix has a very old school setup using bison and flex: https://github

I'll let you decide whether it counts as "mainstream", but the principal implementation of Nix has a very old school setup using bison and flex: https://github.com/NixOS/nix/blob/master/src/libexpr/parser.y https://github.com/NixOS/nix/blob/master/src/libexpr/parser.... https://github.com/NixOS/nix/blob/master/src/libexpr/lexer.l https://github.com/NixOS/nix/blob/master/src/libexpr/lexer.l