
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


data Fifo a = F [a] [a]
 
emptyFifo :: Fifo a
emptyFifo = F [] []
 
push :: Fifo a -> a -> Fifo a
push (F input output) item = F (item:input) output
 
pop :: Fifo a -> (Maybe a, Fifo a)
pop (F input (item:output)) = (Just item, F input output)
pop (F []    []           ) = (Nothing, F [] [])
pop (F input []           ) = pop (F [] (reverse input))
 
isEmpty :: Fifo a -> Bool
isEmpty (F [] []) = True
isEmpty _         = False
 