Truncating results doesn't add anything but confusion to the kata. Should I truncate intermediate results? If not I can't use recursive code. Just don't, and polish up the tests.

It's also practically a double of the Evaluate Mathematical Expression - needed one more line of code for the functions. (Oh, and two minimal adjustments to the tokeniser.)

Still, if you do it right, it adds functions to said kata. It's a lot more interesting to build a parser (again, and again, and again) than to find the umpteenth cheat (again, and again, and again) that hasn't been disabled.

Add more example cases.