PROJECT TITLE: A0 interpreter
See  http://www.radford.edu/itec380/2022spring-ibarland/Homeworks/Project/
AUTHORS: Ian Barland
USER INSTRUCTIONS:
  Test cases are in ExprTest.java.
  The testing framework takes a list of pairs --
  strings (must be legal A0 syntax) and the expected value.
  The testing framework then makes two test for each string:
    it parses the string and toString's the parse tree, expecting back the 
    same input string (up to white space),
  and it parses and evals the string, checking for the expected value.

LICENSE: CC-BY: reuse as you like, but please include attribution.  (URL to source works fine.)