On Mon, Sep 23, 2019, 3:05 PM Juan Casanova <juan.casanova@ed.ac.uk> wrote:

My types:

data SOTermPF fn p f = ConstF fn | Proj Int | CompF p [f] deriving Eq

newtype SOTermF fn f = SOF (SOTermPF fn f f) deriving Eq

Here's a more modular option for the Traversable instance.

import Data.Bitraversable

import Data.Bifoldable

import Control.Applicative

import Data.Traversable

instance Bifoldable (SOTermPF fn) where

bifoldMap = bifoldMapDefault

instance Bitraversable (SOTermPF fn) where

bitraverse _f _g (ConstF fn) = pure (ConstF fn)

bitraverse _f _g (Proj i) = pure (Proj i)

bitraverse f g (CompF p fs) =

liftA2 CompF (f p) (traverse g fs)

instance Foldable (SOTermF fn) where

foldMap = foldMapDefault

instance Traversable (SOTermF fn) where

traverse f (SOF q) = SOF <$> bitraverse f f q