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Using Icon lists as queues

We have seen how the ``push()'' and ``pop()'' function aid in using Icon lists as stacks. Two more functions allow elements to be added and removed from the end of any list:

• ``put(L, x)'' adds x after the old last element of list L.
• ``pull(L)'' removes the last element from list L and returns the value removed.

To sum up, here is a picture of how the four stack and queue functions in Icon work:

   push -->  +--------+--------+-------+--------+  <-- put
             |  L[1]  |  L[2]  |  ...  |  L[*L] |
   pop  <--  +--------+--------+-------+--------+  --> pull