Elm - reworking the FIFO implementation from

01-using-a-node-and-a-list.elm

import Graphics.Element exposing (..)
import Text

type Fifo a
    = Empty | Node a (List a)


empty : Fifo a
empty =
    Empty


insert : a -> Fifo a -> Fifo a
insert a fifo =
    case fifo of
        Empty ->
            Node a []
        
        Node front back ->
            Node front (a :: back)


remove : Fifo a -> ( Maybe a, Fifo a )
remove fifo =
    case fifo of
        Empty ->
            ( Nothing, empty )
            
        Node front [] ->
            ( Just front, empty )

        Node front (next :: rest) ->
            ( Just front, Node next rest )


fromList : List a -> Fifo a
fromList list =
    case list of
        (first :: rest) ->
            Node first rest
        
        [] ->
            empty
    
    
    
toList : Fifo a -> List a
toList fifo =
    case fifo of
        Empty ->
            []
            
        Node front back ->
            [front] ++ List.reverse back
    
    
main =
  empty
      |> insert 9
      |> insert 8
      |> remove |> snd
      |> insert 7
      |> remove |> fst
      |> show