The expression parser did not have an equal function (eg: if a==b then true) but had an extensible structure so I added an 'EQ' function and amazingly it returns the same values as the Handango RPN function so it looks like I can use it. It also has a few techniques which are new to me and a simple self contained string class so I'm glad I persevered.
update: the parser code had bugs so I just hard coded 12 lines to do the Handango reg code stuff. If only Handango had a sane example for developers I could have saved 2 days thinking it was hard when it was easy. No matter I will document for others.