The rest of implementation can be seen in the GitRepo. I have upgraded the original calculator with ComCalc so as to be able to compare. It can be seen here. One thing that I sort of miss from that time is frames. They sure can't compete with dynamic webpages on a server that runs a backend language. But they are easier to use, and the idea still holds - create one menu that can be used on all pages, but only needs to be changed in one file.
The calculator can also be run from Terminus (it is called comcalc). To do so write comcalc "expression" where expression is some math expression.
This projects will be the last of these parser intro projects. The next ones are to be about actual programming languages.