CAS.part() behaviour

[parisse]

As I explained, it does not simplify but it evaluates. When you run test('1+1'), quote(1+1) is evaled to 1+1, then test is called with argument a==1+1, and when return(a) is evaled, a is replaced by 1+1 and evaled to 2.
You must run test(quote(quote(1+1))) to get '1+1'. (Assuming postprocessing with regroup or simplify is disabled in your settings).
It's almost impossible to prevent evaluation. Evaluation will only do simple operations, like adding integers or rational fractions. It will not simplify polynomials or do more complex tasks. Evaluation is required to do most CAS tasks, otherwise some strange things could happen (for example sqrt or division will not work correctly).