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Stack

A :struct:`Stack` is a collection of any type in kOS. Stacks work according to Last-In first-out principle. It may be useful to contrast :struct:`Stack` with :struct:`Queue` to better understand how both structures work. You can read more about stacks on Wikipedia.

Using a stack

SET S TO STACK().
S:PUSH("alice").
S:PUSH("bob").

PRINT S:POP. // will print 'bob'
PRINT S:POP. // will print 'alice'

Structure

.. structure:: Stack

    .. list-table:: Members
        :header-rows: 1
        :widths: 2 1 4

        * - Suffix
          - Type
          - Description

        * - :meth:`PUSH(item)`
          - None
          - add item to the top of the stack
        * - :meth:`POP()`
          - any type
          - returns the item on top of the stack and removes it
        * - :meth:`PEEK()`
          - any type
          - returns the item on top of the stack without removing it
        * - :attr:`LENGTH`
          - integer
          - number of elements in the stack
        * - :meth:`CLEAR()`
          - None
          - remove all elements
        * - :attr:`ITERATOR`
          - :struct:`Iterator`
          - for iterating over the stack
        * - :attr:`COPY`
          - :struct:`Stack`
          - a new copy of this stack
        * - :meth:`CONTAINS(item)`
          - boolean
          - check if stack contains an item
        * - :attr:`EMPTY`
          - boolean
          - check if stack if empty
        * - :attr:`DUMP`
          - string
          - verbose dump of all contained elements




.. method:: Stack:PUSH(item)

    :parameter item: (any type) item to be added

    Adds the item to the top of the stack.


.. method:: Stack:POP()

    Returns the item on top of the stack and removes it.


.. method:: Stack:PEEK()

    Returns the item on top of the stack without removing it.


.. method:: Stack:CLEAR()

    Removes all elements from the stack.


.. attribute:: Stack:LENGTH

    :type: integer
    :access: Get only

    Returns the number of elements in the stack.


.. attribute:: Stack:ITERATOR

    :type: :struct:`Iterator`
    :access: Get only

    An alternate means of iterating over a stack. See: :struct:`Iterator`.


.. attribute:: Stack:COPY

    :type: :struct:`Stack`
    :access: Get only

    Returns a new stack that contains the same thing as the old one.


.. method:: Stack:CONTAINS(item)

    :parameter index: (integer) starting index (from zero)
    :return: boolean

    Returns true if the stack contains an item equal to the one passed as an argument


.. attribute:: Stack:EMPTY

    :type: boolean
    :access: Get only

    Returns true if the stack has zero items in it.


.. attribute:: Stack:DUMP

    :type: string
    :access: Get only

    Returns a string containing a verbose dump of the stack's contents.