I watered it down some.

I am using recursion on parenthesis until I get to a parenthetical set at the innermost level.

Then, I have a list of operands in order-of-operations order. And I loop through the equation reducing the equation by performing each operation in turn until I end up with a single number, then go back out one level.

Still coding, but this level of simplicity is at least getting me somewhere.

I might add functions in at a later date, but not for now. For now, it is straight math (or maths for you singular-impaired folk).