error

src/Diagrams/Trail.hs:150:1:
    Can't make a derived instance of `Transformable (SegTree v)'
      (even with cunning newtype deriving):
      it is not type-safe to use GeneralizedNewtypeDeriving on this class;
      the last parameter of `Transformable' is at role N
    In the stand-alone deriving instance for
      `(HasLinearMap v, InnerSpace v, OrderedField (Scalar v)) =>
       Transformable (SegTree v)'

gistfile1.hs

--- Diagrams.Core.Transform:

-- | Type class for things @t@ which can be transformed.
class HasLinearMap (V t) => Transformable t where

  -- | Apply a transformation to an object.
  transform :: Transformation (V t) -> t -> t


--- Diagrams.Trail

newtype SegTree v = SegTree
                  { getSegTree :: FingerTree (SegMeasure v) (Segment Closed v) }
  deriving (Eq, Ord, Show)


-- But! 
-- V (SegTree v) can be different from V (FingerTree (SegMeasure v) (Segment Closed v)) because of newtypes