Generalise encoder bifunctor instances #1090
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alexfmpe
commented
Jun 30, 2024
| bimap f g = EncoderImpl | ||
| { _encoderImpl_encode = bimap (_encoderImpl_encode f) (_encoderImpl_encode g) | ||
| , _encoderImpl_decode = \(a, b) -> liftA2 (,) (_encoderImpl_decode f a) (_encoderImpl_decode g b) | ||
| , _encoderImpl_decode = bitraverse (_encoderImpl_decode f) (_encoderImpl_decode g) |
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Just as
Naturality
t . traverse f = traverse (t . f) for every applicative transformation t
Identity
traverse Identity = Identitygive us
traverse pure
= traverse ((pure . runIdentity) . Identity)
= (pure . runIdentity) . traverse Identity
= purewe also have bitraverse pure pure = pure and thus
bitraverse df df . bimap ef eg
= bisequence . bimap df dg . bimap ef eg
= bisequence . bimap (df . ef) (dg . eg)
= bisequence . bimap pure pure
= bitraverse pure pure
= pure
alexfmpe
commented
Jun 30, 2024
| second g = bimap id g | ||
| instance Monad parse => Bifunctor (,) (EncoderImpl parse) (EncoderImpl parse) (EncoderImpl parse) where | ||
| instance (Monad parse, Bitraversable p, Bifunctor p (->) (->) (->)) => Bifunctor p (EncoderImpl parse) (EncoderImpl parse) (EncoderImpl parse) where |
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I do wonder whether there can be a Bifunctor p (EncoderImpl parse) (EncoderImpl parse) (EncoderImpl parse) that does anything different than bimap over p a b in the forward direction since it must be able to encode forall a b
As for whether it can do anything besides bitraverse in the backward direction, that equally applies to the Functor (EncoderImpl parse) (EncoderImpl parse) instance
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I have:
developbranchhlint .(lint found code you did not write can be left alone)$(nix-build -A selftest --no-out-link)nix-build release.nix -A build.x86_64-linux --no-out-link(orx86_64-darwinon macOS)