heftia_iso.hs

-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at https://mozilla.org/MPL/2.0/.

newtype Heftia h a = Heftia {unHeftia :: FreerTreeT (h (Heftia h)) Identity a}
    deriving (Functor, Applicative, Monad)

to :: HFunctor h => Heftia h a -> HeftiaTree h a
to (Heftia (FreerTreeT (FreeT (Identity f)))) =
    HeftiaTreeT . HeftyT . Identity $ case f of
        Pure x -> Pure x
        Free (Coyoneda k h) ->
            Free
                . HCoyoneda
                $ Coyoneda
                    (unHeftiaTreeT . to . Heftia . FreerTreeT . k)
                    (hfmap (unHeftiaTreeT . to) h)

from :: HFunctor h => HeftiaTree h a -> Heftia h a
from (HeftiaTreeT (HeftyT (Identity f))) =
    Heftia . FreerTreeT . FreeT . Identity $
        case f of
            Pure x -> Pure x
            Free (HCoyoneda (Coyoneda k h)) ->
                Free $
                    Coyoneda
                        (unFreerTreeT . unHeftia . from . HeftiaTreeT . k)
                        (hfmap (from . HeftiaTreeT) h)

関連する定義はこの辺りに
https://github.com/sayo-hs/heftia/blob/80be242c1fa8dec3a37d5dbf2697321037effe29/heftia/src/Control/Monad/Trans/Heftia/Tree.hs