datatype lines = End | Line of source lines type t = { Head : source lines, Tail : source (source lines) } val create = head <- source End; tail <- source head; return {Head = head, Tail = tail} fun renderL lines = case lines of End => | Line linesS => X
and renderS linesS = lines <- signal linesS; return (renderL lines) fun render t = renderS t.Head fun write t = oldTail <- get t.Tail; newTail <- source End; set oldTail (Line newTail); set t.Tail newTail fun main () : transaction page = b <- create; return