
Data Structure

This illustrates a data structure, a means of storing data within a program.

You may see other such structures in the Data Structures category.
 Illustration of FIFO behavior
Task

Implement a FIFO queue.

Elements are added at one side and popped from the other in the order of insertion.



Operations:

   push   (aka enqueue)    - add element
   pop     (aka dequeue)    - pop first element
   empty                             - return truth value when empty


Errors:

   handle the error of trying to pop from an empty queue (behavior depends on the language and platform)


See

   Queue/Usage   for the built-in FIFO or queue of your language or standard library.


See also

 Array
 Associative array: Creation, Iteration
 Collections
 Compound data type
 Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
 Linked list
 Queue: Definition, Usage
 Set
 Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
 Stack


{ include ..\Utilitys.tlhy }
"..\Utilitys.tlhy" load
 
 
:push!   { l i -- l&i }
    0 put
;
 
:empty?  { l -- flag }
    len not   { len 0 equal }
;
 
:pop!    { l -- l-1 }
    empty? (
        ["Empty"]
        [pop swap]
    ) if
;
 
 
( ) { empty queue }
 
1 push! 2 push! 3 push!
pop! ? pop! ? pop! ? pop! ?
 
"End " input