Give Compose's instances explicit kind signatures
#607
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
RyanGlScott
changed the title
Compose's instances explicit kind signatures
Previously, the promoted versions of certain `Compose` instances (`Functor`, `Foldable`, etc.) would be overly general due to the fact that `singletons-th` omits instance contexts during promotion. For example, the promoted `Functor` instance for `Compose` was: ```hs instance PFunctor (Compose (f :: k -> Type) (g :: Type -> k)) where ... ``` But this was too general, as `f` and `g` should both be of kind `Type -> Type` instead. The defunctionalization symbols associated with the instances also had a similar problem. This patch annotates each instance with an explicit kind (e.g., `Functor (Compose (f :: Type -> Type) g)` to ensure that the promoted instances also have the intended kind. This is very much in the same spirit as the situation described in `Note [Using standalone kind signatures not present in the base library]` in `Control.Monad.Singletons.Internal`, but for instance declarations instead of class declarations. Resolves the "Overly polymorphic instance methods" section of #601.
RyanGlScott
force-pushed
the
explicit-instance-kind-signatures
branch
from
e328357
to
b40498c
Compare
RyanGlScott
added a commit
that referenced
this pull request
Jun 30, 2024
This adds more explicit `Type -> Type` kind signatures to definitions that would otherwise be kind-generalized to have overly polymorphic kinds: * The kinds of `Asum` and `Msum` (the promoted counterparts to the term-level `asum` and `msum` functions, respectively). * The helper type families generated when promoting the `Alternative` and `MonadPlus` instances for `Data.Functor.Product`. This sort of kind polymorphism isn't observable by users in today's GHC, but it will cause problems later in a future version of GHC that implements [GHC#23515](https://gitlab.haskell.org/ghc/ghc/-/issues/23515). (See #601.) (I should have added these as part of #606 or #607, but I forgot them due to an oversight.)
RyanGlScott
added a commit
that referenced
this pull request
Jul 1, 2024
This adds more explicit `Type -> Type` kind signatures to definitions that would otherwise be kind-generalized to have overly polymorphic kinds: * The kinds of `Asum` and `Msum` (the promoted counterparts to the term-level `asum` and `msum` functions, respectively). * The helper type families generated when promoting the `Alternative` and `MonadPlus` instances for `Data.Functor.Product`. This sort of kind polymorphism isn't observable by users in today's GHC, but it will cause problems later in a future version of GHC that implements [GHC#23515](https://gitlab.haskell.org/ghc/ghc/-/issues/23515). (See #601.) (I should have added these as part of #606 or #607, but I forgot them due to an oversight.)
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Previously, the promoted versions of certain
Composeinstances (Functor,Foldable, etc.) would be overly general due to the fact thatsingletons-thomits instance contexts during promotion. For example, the promotedFunctorinstance forComposewas:But this was too general, as
fandgshould both be of kindType -> Typeinstead. The defunctionalization symbols associated with the instances also had a similar problem.This patch annotates each instance with an explicit kind (e.g.,
Functor (Compose (f :: Type -> Type) g)to ensure that the promoted instances also have the intended kind. This is very much in the same spirit as the situation described inNote [Using standalone kind signatures not present in the base library]inControl.Monad.Singletons.Internal, but for instance declarations instead of class declarations.Resolves the "Overly polymorphic instance methods" section of #601.