I'm still working on my little tool for interactive mathematics.
The bulk of the code compiles mathematical expressions and their values into TeX code. Parsing and evaluation is provided by math.js, and I traverse the syntax tree to generate the TeX code.
The intermediate representation is nested string arrays. In retrospect, they are basically S-expressions.
I feel like I need macros now, so I'm dangerously close to creating JSArrayLisp...