e current style after starting a new trail
modifyCurrStyle :: (Floating n, Ord n) =>
                   (PenStyle n -> PenStyle n)
                -> TurtleState n
                -> TurtleState n
modifyCurrStyle f t =  t # makeNewTrail # \t' -> t' { currPenStyle = (f . currPenStyle) t' }

-- Creates a
modifyCurrStyle :: (Floating n, Ord n) =>
                   (PenStyle n -> PenStyle n)
                -> TurtleState n
                -> TurtleState n
modifyCurrStyle f t =  t # makeNewTrail # \t' -> t' { currPenStyle = (f . currPenStyle) t' }
modifyCurrStyle f t =  t # makeNewTrail # \t' -> t' { currPenStyle = (f . currPenStyle) t' }