 list of paths, with current trail added to a "Turtle"’s @paths@ field
addTrailToPath :: (Ord n, Floating n) => TurtleState n
               -> Located (Trail V2 n)
               -> [TurtlePath n]
addTrailToPath t tr
  | isTrailEmpty (unLoc tr) = paths t
  | otherwise               = makeTurtlePath t tr : paths t

-- Starts a 
addTrailToPath :: (Ord n, Floating n) => TurtleState n
               -> Located (Trail V2 n)
               -> [TurtlePath n]
addTrailToPath t tr
  | isTrailEmpty (unLoc tr) = paths t
  | otherwise               = makeTurtlePath t tr : paths t
addTrailToPath t tr
  | isTrailEmpty (unLoc tr) = paths t
  | otherwise               = makeTurtlePath t tr : paths t