Thanks everybody for an illuminating discussion about DeriveAnyClass. I
was not aware of the dark corners of the extension (and actually, now I
find it weird that GHC itself suggests that extension!). Here are my
updated votes; apart from a ’No’ to DeriveAnyClass I’ve updated my votes of
StandaloneKindSignatures and ImportQualifiedPost to ‘Yes’.
-- the ones with comments
CUSKs: no
-- ^ according to the guide, this is superseded by StandaloneKindSignatures
ConstrainedClassMethods: yes
-- ^ it is implied by MultiParamTypeClasses anyway
DefaultSignatures: no
-- ^ as Joachim says, this should be succeeded by DerivingVia
-- ^ anyway, this is one required for the writer of the class, so no big
deal
DeriveAnyClass: no
-- ^ I think this makes no harm, and I tend to use deriving (ToJSON,
FromJSON)
DerivingVia: yes
-- ^ even though it’s quite recent, I think it’s quite sensible and I don’t
foresee many changes to it
DisambiguateRecordFields: no
DuplicateRecordFields: no
-- ^ we seem to still be working on this
FunctionalDependencies: maybe
-- ^ this is a hard one! Not so terrible since it’s only required by the
creator of the class, not of the instances
MonadFailDesugaring: yes
-- ^ isn’t this the default nowadays?
MonoLocalBinds: maybe
-- ^ this is implied by GADTs, but otherwise we shouldn’t
MultiWayIf: no
-- ^ still in discussion
NamedWildCards: yes
-- ^ not many people use this, but I think this is the sane default
OverloadedLists: yes
OverloadedStrings: yes
-- ^ I would love to see these included, but I agree with the sentiment
that they need more work
PartialTypeSignatures: no
-- ^ I really think that partial type signatures should not be accepted by
default
QuantifiedConstraints: maybe
-- ^ too early, may want to refine this
ScopedTypeVariables: yes
-- ^ I think this is really well understood and people want it
PatternSynonyms: maybe
-- ^ we are still working out the edges of this
-- these seem simple syntactic extensions
-- many of them bring compatibility with the syntax of Java-like languages
BinaryLiterals: yes
HexFloatLiterals: yes
NegativeLiterals: yes
NumDecimals: yes
NumericUnderscores: yes
-- too early but wouldn’t care to introduce it
StandaloneKindSignatures: yes
ImportQualifiedPost: yes
-- don’t know
ForeignFunctionInterface: maybe
GHCForeignImportPrim: maybe
InterruptibleFFI: maybe
LexicalNegation: maybe
NondecreasingIndentation: maybe
PackageImports: maybe
ParallelListComp: maybe
StarIsType: maybe
TransformListComp: maybe
UnliftedFFITypes: maybe
UnliftedNewtypes: maybe
UnicodeSyntax: maybe
-- the rest
AllowAmbiguousTypes: no
ApplicativeDo: no
Arrows: no
BangPatterns: yes
BlockArguments: no
CApiFFI: no
CPP: no
ConstraintKinds: yes
DataKinds: yes
DatatypeContexts: no
DeriveDataTypeable: yes
DeriveFoldable: yes
DeriveFunctor: yes
DeriveGeneric: yes
DeriveLift: yes
DeriveTraversable: yes
DerivingStrategies: yes
EmptyCase: yes
EmptyDataDecls: yes
EmptyDataDeriving: yes
ExistentialQuantification: yes
ExplicitForAll: yes
ExplicitNamespaces: no
ExtendedDefaultRules: no
FlexibleContexts: yes
FlexibleInstances: yes
GADTSyntax: yes
-- ^ implied by GADTs anyway
GADTs: yes
GeneralisedNewtypeDeriving: yes
ImplicitParams: no
ImpredicativeTypes: no
IncoherentInstances: no
InstanceSigs: yes
KindSignatures: yes
LambdaCase: yes
LiberalTypeSynonyms: no
LinearTypes: no
MagicHash: no
MonadComprehensions: no
MultiParamTypeClasses: yes
NPlusKPatterns: no
NamedFieldPuns: yes
NoImplicitPrelude: no
NoMonomorphismRestriction: yes
NoPatternGuards: no
NoTraditionalRecordSyntax: no
NullaryTypeClasses: yes
OverlappingInstances: no
OverloadedLabels: no
PolyKinds: yes
PostfixOperators: yes
QualifiedDo: no
QuasiQuotes: no
RankNTypes: no
RebindableSyntax: no
RecordWildCards: yes
RecursiveDo: no
RoleAnnotations: no
Safe: no
StandaloneDeriving: yes
StaticPointers: no
Strict: no
StrictData: no
TemplateHaskell: no
TemplateHaskellQuotes: no
Trustworthy: no
TupleSections: yes
TypeApplications: yes
TypeFamilies: yes
TypeFamilyDependencies: no
TypeInType: maybe
TypeOperators: yes
TypeSynonymInstances: yes
UnboxedSums: no
UnboxedTuples: no
UndecidableInstances: no
UndecidableSuperClasses: no
Unsafe: no
ViewPatterns: yes
On 30 Nov 2020 at 18:33:55, Richard Eisenberg
I also adopted Iavor's very helpful categorization.
I have not given any motivations below, as it's too difficult to read everyone's motivations inline. Instead, I give several varieties of "no" votes. Let's debate when someone disagrees with me. (To be clear: "obscure" just means that someone should manually opt in, not that the feature is really obscure.)
*Module System=============*
ImportQualifiedPost: yes PackageImports: obscure NoImplicitPrelude: breaking
*Notation========*
BlockArguments: yes MultiWayIf: might change LambdaCase: might change BinaryLiterals: yes HexFloatLiterals: yes NumericUnderscores: yes NumDecimals: yes OverloadedStrings: bad for beginners OverloadedLists: bad for beginners OverloadedLabels: obscure EmptyCase: yes PostfixOperators: yes LexicalNegation: yes UnicodeSyntax: yes NegativeLiterals: superseded TupleSections: yes ImplicitParams: obscure ParallelListComp: yes RecursiveDo: obscure TransformListComp: obscure Arrows: obscure ApplicativeDo: breaking QualifiedDo: too fresh MonadComprehensions: bad for beginners NondecreasingIndentation: obscure RebindableSyntax: breaking ExplicitNamespaces: yes
*Data Types==========* DatatypeContexts: no ExistentialQuantification: yes EmptyDataDecls: yes RoleAnnotations: yes StrictData: breaking GADTSyntax: yes GADTs: obscure
*Patterns and Guards===================*
BangPatterns: yes ViewPatterns: yes PatternSynonyms: too fresh NoPatternGuards: breaking NPlusKPatterns: deprecated
*Records=======*
NamedFieldPuns: yes RecordWildCards: confusing DisambiguateRecordFields: yes DuplicateRecordFields: might change NoTraditionalRecordSyntax: no
*Deriving=======*
DeriveGeneric: yes DeriveLift: yes DeriveDataTypeable: yes EmptyDataDeriving: yes StandaloneDeriving: yes DeriveFunctor: yes DeriveFoldable: yes DeriveTraversable: yes DerivingStrategies: yes DerivingVia: yes GeneralisedNewtypeDeriving: yes DeriveAnyClass: dangerous
*Class System============*
MultiParamTypeClasses: yes NullaryTypeClasses: superseded ConstraintKinds: yes TypeSynonymInstances: yes FlexibleInstances: yes FlexibleContexts: yes ConstrainedClassMethods: yes DefaultSignatures: yes InstanceSigs: yes ExtendedDefaultRules: might change FunctionalDependencies: obscure QuantifiedConstraints: too fresh UndecidableInstances: dangerous IncoherentInstances: dangerous UndecidableSuperClasses: dangerous OverlappingInstances: superseded
Types *=====*
RankNTypes: yes StandaloneKindSignatures: yes KindSignatures: yes LiberalTypeSynonyms: confusing ScopedTypeVariables: might change ExplicitForAll: yes AllowAmbiguousTypes: dangerous ImpredicativeTypes: too fresh MonoLocalBinds: breaking NoMonomorphismRestriction: debate! PartialTypeSignatures: obscure NamedWildCards: yes LinearTypes: too fresh TypeApplications: yes PolyKinds: yes TypeOperators: yes StarIsType: deprecated TypeFamilies: obscure TypeFamilyDependencies: obscure DataKinds: might change
*FFI===*
ForeignFunctionInterface: obscure CApiFFI: obscure GHCForeignImportPrim: obscure InterruptibleFFI: obscure UnliftedFFITypes: obscure StaticPointers: obscure
*Low Level=========*
UnboxedSums: obscure UnboxedTuples: obscure MagicHash: obscure UnliftedNewtypes: yes
*Macros======*
CPP: obscure TemplateHaskell: TH TemplateHaskellQuotes: yes QuasiQuotes: TH
*Other=====*
Unsafe: no Safe: no Trustworthy: no Strict: no
*Obsolete/Deprecated===================*
CUSKs: no TypeInType: no MonadFailDesugaring: maybe