Undo Manager in JavaFX

gistfile1.as

public class Undoable {
    public var undo: function(): Void;
    public var redo: function(): Void;
}

public class UndoManager {

    public-init var limit = 10;

    public-read var redoable: Boolean;

    public-read var undoable: Boolean;
    
    var undoables: Undoable[];

    var pos = -1 on replace {
        redoable = (pos < sizeof undoables - 1);
        undoable = (-1 < pos);
    }

    public function redo(): Void {
        if (redoable) {
            undoables[++pos].redo();
        }
    }

    public function undo(): Void {
        if (undoable) { 
            undoables[pos].undo();
            pos--;
        }
    }

    public function add(undoable: Undoable) {
        delete undoables[pos + 1..];
        insert undoable into undoables;
        pos++;

        if (sizeof undoables >  limit) {
            delete undoables[0];
            pos--;
        }
    }
}