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For generic decoding, `Decode (Foo a)` needs a `Decode a` constraint, but it *doesn't* need a `Generic a` constraint. Adding in this unnecessary constraint creates needless problems like, "there isn't an instance for `Generic String _`."
PureScript isn't happy with eta-reduced typeclass instances on recursive types. We have to make the function application explicit.
…y (Container A)`. The generated code will include an `Eq a =>` constraint.
* Sum types where every constructor has zero arguments. Aeson has special handling for these.
For generic decoding, `Decode (Foo a)` needs a `Decode a` constraint, but it *doesn't* need a `Generic a` constraint. Adding in this unnecessary constraint creates needless problems like, "there isn't an instance for `Generic String _`."
…xy (Container A)`. The generated code will include an `Ord a =>` constraint.
It turns out you can't eta-reduce typeclass instances for recursively-defined typeclasses in PureScript. That is: `show = genericShow` ...has to be replaced with: `show x = genericShow` ...to work reliably. See: purescript/purescript#2975
That is, `(genericShow <*> mkSumType) (Proxy @(Foo A))` will generate: ``` instance showFoo :: Show a => Show (Foo a) where show = genericShow ``` ...whereas before it would have missed out the `Show a` constraint.
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Once purescript/spago#1310 is merged and Spago is updated via |
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@kindaro @peterbecich do you also find that for newer GHC releases |
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get Spago 0.93.44 use ghc 9.8 update spago.lock
replace Magic Nix Cache with https://github.com/nix-community/cache-nix-action
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@eskimor , @flip111 , @kindaro , please review This branch is in a working state. Test and example coverage is excellent. This PR should not be a regression. The library is easier to iterate and test now. For any issues that still exist, it should be easier for myself and others to follow up on them. |
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#63
CodeGenSwitchesno longer usedProxyno longer usedPrinterusesLeijen.Textinstead ofTextgenericShowPureScript instanceShow#85instanceToImportLinesinstead of being divided between two modulesRoundTriptests implemented by IOHKjson-helpersand exposes issuesTODO
check that derivedGenericinstances are correctfixRoundTriptestsome other broken testsThe PR supports https://github.com/input-output-hk/purescript-bridge-json-helpers and the existing library https://github.com/coot/purescript-argonaut-aeson-generic
The issues with
purescript-argonaut-aeson-genericare documented in the readme. Importantly, these issues exist onmasterright now without the PR, so I think it should not block merging. Discussion purescript-contrib/purescript-argonaut-codecs#115 (comment)The other library https://github.com/paf31/purescript-foreign-generic continues to be supported, but the test coverage is much less than the other two.