I've added curveto operation and replaced pen-up and pen-down with moveto. I wonder how I didn't initially spot that moveto is as expressive as pen-up / pen-down, less complicated and already present in PostScript...
Also I've added "vamps" on paths - these are basically a moveto combined with a drawn decorative path. Only the moveto forms part of the accumulated path - the dotted square in the doodle below is drawn with a vamp:
