a simple arithmetic calculator, written in c++, implementing a lexer, a recursive decent ll(2) parser, and a visitor for compiling ast.
./PROG_NAME input.txt
input.txt:
pi = 3.1416
r = 123
area = pi * ( r * r )
area
(assuming that the excutable is named calc.exe)
> calc.exe input.txt
> 47529.264790