In functional programming you would store actions in lists with funs/closures inside those data. For example in erlang list of undo actions would look like this

In functional programming you would store actions in lists with funs/closures inside those data. For example in erlang list of undo actions would look like this: Undo = [ { RemoveJpeg, JpegData} ] where RemoveJpeg is a fun (like closure) and JpegData is what would be given as argument to this fun. The implementing undo looks like this: undo_action(Document,[UndoHead|UndoTail]) -> {UndoFun,UndoData} = UndoHead, UndoFun(Document,UndoData). Isn't it simple? RemoveJpeg just returns modified document. undo_action knows only that every action should take two arguments and return modified document.