In the language in which you plan to work, implement an interpreter for a simple arithmetic language.

The language has to include:
- numbers
- a few arithmetic operations

That's it!

As many of you took Programming Languages last quarter, you have recently
solved this (and many similar) problem(s) in Scheme.  If you're one of these
people, I would encourage you to solve this lab in a different language, and
then compare that solution to the one you wrote in Scheme.

You must specify test cases.  If you don't write test cases, I will assume that
your code is incorrect.

For this lab, you're not required to build any kind of parser.  That is, you
may define your abstract syntax trees any way you like, and specify your test
cases by passing ASTs to the interpreter.