There's no new syntax. Notice what the labels and gotos look like: label .error goto .error They are just method accesses on the global variables "l

There's no new syntax. Notice what the labels and gotos look like: label .error goto .error They are just method accesses on the global variables "label" and "goto". The OP just looks through the compiled byte code for access to them, saving the locations of the labels before replacing them with NOPs and replacing the gotos with jumps to the labels' locations. Cute.