tasks a-s

Task/Queue-Definition/Haskell/queue-definition-1.hs

@@ -0,0 +1,16 @@
+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