Four types of RPN

[Marcus von Cube]

(09-02-2014 10:52 PM)hansklav Wrote:  Imho your descriptive classification for the top of the stack is not entirely accurate, and misses the important point of presence or absense of "top copy on pop".

I don't like this wording because it doesn't describe exactly what happens:

In the RPL machines and the Prime, the stack is of variable size. If a value is popped off the stack (consumed or dropped) the length of the stack decreases. Thus, the stack may well contain too little objects to perform a given operation. The prime differs just in the maximum size of this stack from the RPL machines.

In the other machines the stack has a fixed size. The question is what happens if a value is dropped or consumed: The remaining elements drop one level, except the top of the stack which is left unchanged. The duplication of the value is just a side effect of the drop, not an extra operation.