A simple command line calculator written in Rust

Rust calculator
Enter expression to calculate (or 'quit' to exit)
> (1+2) * 3 / 5
res = 1.8
> 2 ^3
res = 8
> d
Invalid character: d
Error: Invalid expression
> quit

It supports parenthesis ( , ) and some simple operators '+' , '-' , '*' ,'/', '^'.