[#82] Remove maybeT, add diOptional #101
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| @@ -25,6 +25,8 @@ The change log is available [on GitHub][2]. | |||
| Improve `Double` generator for property-based tests. | |||
| * Add support for GHC 8.6.1. | |||
| Drop support for GHC 8.0.2. | |||
| * [#82](https://github.com/kowainik/tomland/issues/82): | |||
| Remove `maybeT`. Add `diOptional`. | |||
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Could you also bump up cabal-version in .cabal file as well? I see that it's still 0.4.1 for a very long time...
src/Toml/Bi/Combinators.hs
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| @@ -16,8 +16,8 @@ module Toml.Bi.Combinators | |||
| , arrayOf | |||
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| -- * Combinators | |||
| , diOptional | |||
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The O letter should be small, so it's just dioptional. Standard naming convention for profunctor functions
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Also, since function works with general Codec, it should go to the Toml.Bi.Monad module
src/Toml/Bi/Combinators.hs
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| maybeT :: forall a . (Key -> TomlCodec a) -> Key -> TomlCodec (Maybe a) | ||
| maybeT converter key = let codec = converter key in Codec | ||
| { codecRead = (Just <$> codecRead codec) `catchError` handleNotFound | ||
| diOptional :: (Functor r, Functor w, Applicative w) => Codec r w c a -> Codec r w (Maybe c) (Maybe a) |
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Functor is a superclass of Applicative, so it's enough to have only Applicative w in the constraints.
src/Toml/Bi/Combinators.hs
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| , codecWrite = \case | ||
| Nothing -> pure Nothing | ||
| Just v -> codecWrite codec v >> pure (Just v) | ||
| Just c -> Just <$> codecWrite c |
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Nice! You've just implemented Traversable instance for Maybe. If you look at this instance, you probably might notice how to implement codecWrite in more concise way:
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If so, maybe someday I will implement somewhat function for relude :)
src/Toml/Bi/Combinators.hs
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| maybeT converter key = let codec = converter key in Codec | ||
| { codecRead = (Just <$> codecRead codec) `catchError` handleNotFound | ||
| diOptional :: (Functor r, Functor w, Applicative w) => Codec r w c a -> Codec r w (Maybe c) (Maybe a) | ||
| diOptional Codec {..} = Codec |
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There should be no space between Codec and {..}
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Travis fails with an error for |
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@vrom911 Thank you very much for working on this! 💖 |
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It seems it fixed itself. Version |
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While I slept the problem with |
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Resolves: #82