Deriving Eq #148
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Deriving Eq #148
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lukaszcz
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This pr adds automatic implementation of `Eq` instances for inductive
types. To create such an instance the user will use the same syntax as a
regular instance with two differences.
1. It is prefixed with the `deriving` keyword.
2. It has no body.
E.g.
```
deriving instance
eqProductI {A B} {{Eq A}} {{Eq B}} : Eq (Pair A B);
```
This desugars into an instance that returns true when the constructors
match and all arguments are equal according to their respective
instances. There is no special handling of type errors occurring in the
generated code. I.e. if the user forgets a necessary instance argument
in the type signature, a type error will occur in the generated code.
## Stdlib PR
- anoma/juvix-stdlib#148
# Future work
* In the future we should look at
https://www.dreixel.net/research/pdf/gdmh_nocolor.pdf
* See also:
https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/generic-deriving
---------
Co-authored-by: Lukasz Czajka <[email protected]>
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Replaces the existing
Eqinstance of some types by a deriving instance.