Learning the Octave interpreter code to implement Java class dot-referencing

Hi, Octave maintainers,

A while ago, I took a stab at adding support for dot-reference syntax
for Java classes. (https://savannah.gnu.org/bugs/index.php?41239) I
totally failed, because I don't understand the Octave interpreter code
well enough, and don't have bison/yacc skills.

Can anyone point me at resources for learning about the Octave
interpreter code, or bison/yacc generically, that would help me get good
enough to write a patch for this?

Cheers,
Andrew