I could see this being useful, actually. Flesh it out with a bunch of options (no-variables, linear, quadratic, parens, constant ranges, number of terms, etc) and it could really help teach concepts. I remember my wife was studying for a math test and she kept getting tricked up on negative integer multiplication and division. I built something exactly like this on the command line (only in that small domain) and she was able to do 30-40 problems in just 5 minutes. It really made it all sink in and stay there.