pop
==============================================

Purpose
----------------

Provides access to a last-in, first-out stack for matrices.

.. _pop:
.. index:: pop

Format
----------------

::

    pop b;
    pop a;

Remarks
-------

This is used with `gosub`, `goto`, and `return` statements with parameters. It
permits passing parameters to subroutines or labels, and returning
parameters from subroutines.

The `gosub` syntax allows an implicit `push` statement. This syntax is
almost the same as that of a standard `gosub`, except that the matrices to
be `push`'ed "into the subroutine" are in parentheses following the label
name. The matrices to be `push`'ed back to the main body of the program
are in parentheses following the `return` statement. The only limit on the
number of matrices that can be passed to and from subroutines in this
way is the amount of room on the stack.

No matrix expressions can be executed between the (implicit) `push` and
the `pop`. Execution of such expressions will alter what is on the stack.

Matrices must be `pop`'ped in the reverse order that they are `push`'ed,
therefore in the statements:

::

    goto label(x,y,z);
     .
     .
     .
    label:
    pop c;
    pop b;
    pop a;

After the code above:

::

    c = z
    b = y
    a = x

Note that there must be a separate `pop` statement for each matrix popped.

.. seealso:: Functions `gosub`, `goto`, :func:`return`