Postfix Math Expressions

forget what i said - i thought you planned to process an if-then-else statement through that calculator...
if it's for determining whether a condition is true or false then you've got everything. you may want to add a NOT operator whatever true/false value is at the top of the stack. this is the equivalent of CHS (change sign aka unary minus for numbers.

Not yet.

I'll eventually have a NOT operator ~ that does bitwise NOT, and a unary negation operator, perhaps u- (unary -).

I've added these. Unary + and - are u+ and u-, respectively.