I did a little more mutation testing, but it's getting a little boring, so I'm taking a break like I should be anyway.
I took a look at Rosetta Code tasks, and tried to adapt the Arithmetic Evaluation task to my sensibilities. This was kind of tricky because the Python code I based it off of was abbreviated to the point of obfuscation, and the error handling was so confusing that I worked out just enough to strip most of it out. I haven't yet expanded all of the names to something sensible. Trying this out has me firmly on the side of "make a multiple dispatch decorator" now, so I'll get into that next and see about cleaning things up. After that, I'll probably try implementing red-black trees along the lines of Germane and Might, referring also to a previous time I tried to do that.
I spaced out thinking about some other stuff, so I need to call this now.