Add decoding utils#984
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alexfmpe
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Sep 11, 2022
| => (err -> (b -> parse a) -> (b -> parse a)) | ||
| -> Encoder check parse a b | ||
| -> Encoder check parse a b | ||
| retryEncoder retry = unsafeWrapDecoding $ \p b -> catchError (p b) $ \e -> retry e p b |
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Note this only satisfies unsafeWrapDecoding's law if we can trust MonadError to preserve success (well, non-failure). Which I wager we should, but the documentation has no laws whatsoever.
Currently being discussed in the mailing list: https://mail.haskell.org/pipermail/libraries/2022-September/031621.html
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alexfmpe
commented
Sep 26, 2022
| -- Thus, to produce a law-abiding encoder, we need only preserve parse success. | ||
| unsafeWrapDecoding | ||
| :: Functor check | ||
| => ((b -> parse a) -> (b -> parse' a)) -- ^ Required law for @wrap@ argument: @forall a b. p b = pure a => wrap p b = pure a@ |
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It seems hoistParse also implicitly relies on a simplified version of this law, having wrap = (f,). For instance
hoistParse $ const $ throwError "bla"will break roundtrips when we're encoding from inhabited types.
Should it be renamed to have an unsafe prefix?
ryantrinkle
reviewed
Oct 5, 2024
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| -- | Completely override the decoding function. | ||
| -- Since the only 'Encoder' law is round-tripping, values that fail to parse are unconstrained. | ||
| -- Thus, to produce a law-abiding encoder, we need only preserve parse success. |
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"preserve the value of successful parses", not just their successfulness
ryantrinkle
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Oct 5, 2024
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Original motivation was supporting some kind of canonicalization to allow each route to be decoded to from several urls. A lot of semantic agony later, this is what I ended up with.
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)