Add Ord (Tree a) instance.
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I assume this is an oversight because we do have `Ord1 Tree`. Some of you may be interested in knowing that I caught this due to trying out the the changes discusssed in the thread that began in https://mail.haskell.org/pipermail/libraries/2020-March/030306.html.
sjakobi
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Jan 4, 2021
|
Thanks. Yes, this is quite clearly an oversight. |
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` clases where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Show (f (g a)) => Show (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` clases where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Ord (f a)` and `Ord1 f` are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` clases where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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…make non-breaking The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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… Class2 to make non-breaking This change is approved by the Core Libraries commitee in haskell/core-libraries-committee#10 The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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… Class2 to make non-breaking This change is approved by the Core Libraries commitee in haskell/core-libraries-committee#10 The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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… Class2 to make non-breaking This change is approved by the Core Libraries commitee in haskell/core-libraries-committee#10 The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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… Class2 to make non-breaking This change is approved by the Core Libraries commitee in haskell/core-libraries-committee#10 The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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… Class2 to make non-breaking This change is approved by the Core Libraries commitee in haskell/core-libraries-committee#10 The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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Sep 20, 2022
… Class2 to make non-breaking This change is approved by the Core Libraries commitee in haskell/core-libraries-committee#10 The first change makes the `Eq`, `Ord`, `Show`, and `Read` instances for `Sum`, `Product`, and `Compose` match those for `:+:`, `:*:`, and `:.:`. These have the proper flexible contexts that are exactly what the instance needs: For example, instead of ```haskell instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where (==) = eq1 ``` we do ```haskell deriving instance Eq (f (g a)) => Eq (Compose f g a) ``` But, that change alone is rather breaking, because until now `Eq (f a)` and `Eq1 f` (and respectively the other classes and their `*1` equivalents too) are *incomparable* constraints. This has always been an annoyance of working with the `*1` classes, and now it would rear it's head one last time as an pesky migration. Instead, we give the `*1` classes superclasses, like so: ```haskell (forall a. Eq a => Eq (f a)) => Eq1 f ``` along with some laws that canonicity is preserved, like: ```haskell liftEq (==) = (==) ``` and likewise for `*2` classes: ```haskell (forall a. Eq a => Eq1 (f a)) => Eq2 f ``` and laws: ```haskell liftEq2 (==) = liftEq1 ``` The `*1` classes also have default methods using the `*2` classes where possible. What this means, as explained in the docs, is that `*1` classes really are generations of the regular classes, indicating that the methods can be split into a canonical lifting combined with a canonical inner, with the super class "witnessing" the laws[1] in a fashion. Circling back to the pragmatics of migrating, note that the superclass means evidence for the old `Sum`, `Product`, and `Compose` instances is (more than) sufficient, so breakage is less likely --- as long no instances are "missing", existing polymorphic code will continue to work. Breakage can occur when a datatype implements the `*1` class but not the corresponding regular class, but this is almost certainly an oversight. For example, containers made that mistake for `Tree` and `Ord`, which I fixed in haskell/containers#761, but fixing the issue by adding `Ord1` was extremely *un*controversial. `Generically1` was also missing `Eq`, `Ord`, `Read,` and `Show` instances. It is unlikely this would have been caught without implementing this change. ----- [1]: In fact, someday, when the laws are part of the language and not only documentation, we might be able to drop the superclass field of the dictionary by using the laws to recover the superclass in an instance-agnostic manner, e.g. with a *non*-overloaded function with type: ```haskell DictEq1 f -> DictEq a -> DictEq (f a) ``` But I don't wish to get into optomizations now, just demonstrate the close relationship between the law and the superclass. Bump haddock submodule because of test output changing.
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I assume this is an oversight because we do have
Ord1 Tree.Some of you may be interested in knowing that I caught this due to trying out the the changes discusssed in the thread that began in https://mail.haskell.org/pipermail/libraries/2020-March/030306.html.