Re: [Haskell-cafe] Foldable, Traversable and choosing an order

That is lovely. Makes it super clear. Hadn't thought about Bitraversable and Bifoldable. Thanks a lot. Juan. Quoting David Feuer on Tue, 24 Sep 2019 18:09:08 -0400:

On Mon, Sep 23, 2019, 3:05 PM Juan Casanova wrote:

My types:

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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

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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

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