tasks a-s

Task/Queue-Definition/REBOL/queue-definition.rebol

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+rebol [
+    Title: "FIFO"
+    Author: oofoe
+    Date: 2009-12-11
+    URL: http://rosettacode.org/wiki/FIFO
+]
+
+; Define fifo class:
+
+fifo: make object! [
+	queue: copy []
+	push:  func [x][append queue x]
+	pop:   func [/local x][   ; Make 'x' local so it won't pollute global namespace.
+		if empty [return none]
+		x: first queue  remove queue  x]
+	empty: does [empty? queue]
+]
+
+; Create and populate a FIFO:
+
+q: make fifo []
+q/push 'a
+q/push 2
+q/push USD$12.34              ; Did I mention that REBOL has 'money!' datatype?
+q/push [Athos Porthos Aramis] ; List elements pushed on one by one.
+q/push [[Huey Dewey Lewey]]   ; This list is preserved as a list.
+
+; Dump it out, with narrative:
+
+print rejoin ["Queue is "  either q/empty [""]["not "]  "empty."]
+while [not q/empty][print ["  " q/pop]]
+print rejoin ["Queue is "  either q/empty [""]["not "]  "empty."]
+print ["Trying to pop an empty queue yields:" q/pop]