[ghc-steering-committee] #380 GHC2021: Voting starts

Simon Marlow marlowsd at gmail.com
Tue Dec 1 17:30:57 UTC 2020

I will also change DeriveAnyClass to no:

## Uncontroversial extensions

I've been writing code with most of these enabled by default for quite
some time now. It saves a lot of LANGUAGE pragmas. Other than
RecordWildCards I doubt any of these are controversial.

BangPatterns: yes
BinaryLiterals: yes
DataKinds: yes
DeriveDataTypeable: yes
DeriveGeneric: yes
EmptyCase: yes
ExistentialQuantification: yes
FlexibleContexts: yes
FlexibleInstances: yes
GADTs: yes
GeneralisedNewtypeDeriving: yes
LambdaCase: yes
MultiParamTypeClasses: yes
MultiWayIf: yes
NoMonomorphismRestriction: yes
OverloadedStrings: yes
PatternSynonyms: yes
RankNTypes: yes
RecordWildCards: yes
ScopedTypeVariables: yes
StandaloneDeriving: yes
TupleSections: yes
TypeFamilies: yes
TypeSynonymInstances: yes
NondecreasingIndentation: yes
ConstrainedClassMethods: yes
ConstraintKinds: yes
DefaultSignatures: yes
DeriveFoldable: yes
DeriveFunctor: yes
DeriveTraversable: yes
EmptyDataDecls: yes
EmptyDataDeriving: yes
HexFloatLiterals: yes
ImportQualifiedPost: yes
InstanceSigs: yes
KindSignatures: yes
LiberalTypeSynonyms: yes
NamedFieldPuns: yes
  (I don't personally like this, but I can't justify having
  RecordWildcards but not having this)
NegativeLiterals: yes
NumDecimals: yes
PolyKinds: yes
PostfixOperators: yes
UnicodeSyntax: yes
  (but only the language extension, not the UI changes)

## Extensions that are implied by others, or are irrelevant:

GADTSyntax: yes
ExplicitForAll: yes
MonadFailDesugaring: irrelevant
MonoLocalBinds: yes

## Extensions that are deprecated or exist for legacy reasons:

DatatypeContexts: no
NPlusKPatterns: no
CUSKs: no
NoPatternGuards: no
ForeignFunctionInterface: yes
  (already implied by Haskell2010, why do we have this but
NullaryTypeClasses: no
OverlappingInstances: no
IncoherentInstances: no
TypeInType: no

## No to extensions that are too new to include in GHC2021:

QualifiedDo: no
LinearTypes: no
BlockArguments: no
LexicalNegation: no
QuantifiedConstraints: no
StandaloneKindSignatures: no
StarIsType: no

## No to extensions that are opt-in by design:

ApplicativeDo: no
  (can lead to non-deterministic behaviour with non-rule-abiding
  Applicative instances)
PackageImports: no
CPP: no
DeriveLift: no
  (only makes sense with TemplateHaskell, which is opt-in)
TemplateHaskell: no
TemplateHaskellQuotes: no
QuasiQuotes: no
RebindableSyntax: no
Safe: no
Strict: no
StrictData: no
Trustworthy: no
Unsafe: no
ExtendedDefaultRules: no
NoImplicitPrelude: no

## No to unsafe extensions:

UndecidableInstances: no
UndecidableSuperClasses: no

## No to low-level extensions, not intended to be on by default:

UnboxedTuples: no
UnboxedSums: no
MagicHash: no
UnliftedFFITypes: no
UnliftedNewtypes: no
GHCForeignImportPrim: no
InterruptibleFFI: no

## No to record-related extensions

Records are in flux, let's not do any of this in GHC2021.

DisambiguateRecordFields: no
DuplicateRecordFields: no
NoTraditionalRecordSyntax: no
OverloadedLabels: no

## The rest

That leaves some tricky ones, I'm putting all these as "no" or
"maybe"; we could conservatively just say "no" to all of them.

I'm voting NO on these:

Arrows: no
  (not widely used)
ImplicitParams: no
  (not widely used; questionable semantics; functionality available
  with reflection package)
ImpredicativeTypes: no
  (I don't think we want this on by default, right?)
ParallelListComp: no
  (not widely used, most uses are covered by zip)
StaticPointers: no
  (quite a niche extension, only really useful with Distributed Haskell)
TransformListComp: no
  (not widely used)
ViewPatterns: no
  (not widely used, and in my opinion not a good design)
DeriveAnyClass: no
  (see discussion on the mailing list)

I'm undecided on these:

AllowAmbiguousTypes: maybe
TypeApplications: maybe
CApiFFI: maybe
  (harmless, but a bit niche)
DerivingVia: maybe
  (not very widely-used, quite new)
DerivingStrategies: maybe
  (not very widely-used, quite new)
FunctionalDependencies: maybe
  (slightly inclined to "no", given the overlap
  with TypeFamilies and the lack of widespread usage)
ExplicitNamespaces: maybe
  (might change, so defer?)
MonadComprehensions: maybe
  (does this make error messages worse?)
PartialTypeSignatures: maybe
NamedWildCards: maybe
NumericUnderscores: maybe
OverloadedLists: maybe
  (impact on error messages?)
RecursiveDo: maybe
  (but introduced by a keyword so relatively harmless)
RoleAnnotations: maybe
  (not widely used, but when you need it you need it)
TypeFamilyDependencies: maybe
  (not widely used, but when you need it you need it)
TypeOperators: maybe

On Tue, 1 Dec 2020 at 08:51, Joachim Breitner <mail at joachim-breitner.de>

> Hi,
> Am Dienstag, den 01.12.2020, 00:43 -0800 schrieb Alejandro Serrano
> Mena:
> > 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
> Noted!
> > apart from a ’No’ to DeriveAnyClass I’ve updated my votes of
> > StandaloneKindSignatures and ImportQualifiedPost to ‘Yes’.
> JFTR, you also changed OverloadedLists and OverloadedStrings from maybe
> to yes.
> Cheers,
> Joachim
> --
> Joachim Breitner
>   mail at joachim-breitner.de
>   http://www.joachim-breitner.de/
> _______________________________________________
> ghc-steering-committee mailing list
> ghc-steering-committee at haskell.org
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
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