-------------
Expression: 2 + 3
Result:     5
-------------
Expression: 1 + (2 + 4) / 3
Result:     3
-------------
Expression: 2 ** 3 ** 4
Result:     2.41785163922926e+24
-------------
Expression: 12345.fmt("%.3e")
Result:     1.234e+04
-------------
Expression: 0xFF
Result:     255
-------------
Expression: PI
Result:     3.14159
-------------
Expression: PI * r ** 2
Result:     7.0685775
-------------
Expression: 1 + (
Error:      Missing close )
-------------
Expression: foo
Result:
-------------
Expression: (foo = 123456 + 1)
Result:     123457
-------------
Expression: foo
Result:     123457