Made Up Programming Language - Calculator

The calculator supports the following feature:

1. Linear combination (+, -)
2. Multiplication and division (*, /)
3. Local binding (id = exp)
4. Square root operation (sqrt)
5. List all local bindings (list)
6. Clear all or specific local bindings (clear id; clear)
7. Unary minus operators (-(a + b))
8. Error message (such as undefined local variables, unclosed parenthese, etc.)
9. Exit command (exit; quit)

Usage

    > ruby calc.rb