4 function calculator in Lua

[Foster Schucker <Foster@...>]

One of the things I try to do when learning a new language is how to 
make a 4 function calculator.

Roberto has posted an intro to his Building a Programming Language class 
https://www.youtube.com/playlist?list=PLXPoQXrP0261ceYEnDd5LaZy2UM_4hLae 
and uses LPEG to do pattern matching.   I would not have thought of it 
as a way to do a simple (or complex) calculator.  A good example set if 
you've never used LPEG (like me)