HIDE function hides some levels of the stack to the rest of the executing code. This allows a kind of protection for levels which should not be accessed by a macro call for example. Note that this is not a real protection since a call to
SHOW could reveal the hidden levels.
The hidden levels are always the deepest. Depending on the
levels parameter to the call to
HIDE, the hidden levels could be the whole stack (
levels == 0), a maximum number of levels (
levels >= 0) or a number of levels such that there remains at most a certain number ((abs(
levels < 0).
When called with
NULL as parameter,
HIDE will hide all the visible levels.
The number of newly hidden levels is returned.