[ghc-steering-committee] #167: Deprecated Entities, rec: accept

Sat Mar 9 21:10:18 UTC 2019

My argument for `data` is as follows (quoted from earlier writing of mine):

---
Though I understand the reasons against it, I'm an unabashed supporter of using the word "data" to supplant "pattern". My principal argument is that data can be used freely in the syntax, given that it's a keyword that has current meaning only as the first lexeme in a top-level declaration. (Specifically, I pine for a future where types and terms mix. We can then use type and data in the middle of expressions/types to denote namespaces.) It also works nicely to mean "data constructor". I agree that it doesn't work as well with functions or the potential confusion around "data Bool = True | False" (though, in that last example, we can pretend hard that the data applies only to the bits after the =). 
---

In other words, I think `data` is more future-compatible than any of the alternatives, even though I agree that `value` flows more smoothly. We can think of `data` as meaning "data-level", not "data constructor" (though that admittedly takes a bit of mental gymnastics).

Richard

> On Mar 8, 2019, at 1:12 PM, Vitaly Bragilevsky <bravit111 at gmail.com> wrote:
> 
> I think we don't have a consensus on the particular word yet: is it data or value. I'd like to listen to Richard who was strongly in favor of data. We are in agreement about consistency though.
> 
> Vitaly
> 
> 
> On Fri, Mar 8, 2019 at 8:45 PM Joachim Breitner <mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>> wrote:
> Hi,
> 
> I fully support this (I thought I brought it up before, but maybe not
> strongly enough).
> 
> Should we just include this change in #167? (If politicians can add
> random riders to laws, so can we). Or does it need more thought?
> 
> Cheers,
> Joachim
> 
> 
> Am Freitag, den 08.03.2019, 14:46 +0000 schrieb Simon Peyton Jones via
> ghc-steering-committee:
> > I also argue that, to be consistent, whatever keyword we agree, we should use it
> > In the (accepted) infix/WARNING proposal
> > In import and export lists – presumably for now in addition to ‘pattern’, though we might end up deprecating the latter.
> > Simon
> >  
> > From: Vitaly Bragilevsky <bravit111 at gmail.com <mailto:bravit111 at gmail.com>> 
> > Sent: 08 March 2019 14:44
> > To: Simon Peyton Jones <simonpj at microsoft.com <mailto:simonpj at microsoft.com>>
> > Cc: Simon Marlow <marlowsd at gmail.com <mailto:marlowsd at gmail.com>>; ghc-steering-committee <ghc-steering-committee at haskell.org <mailto:ghc-steering-committee at haskell.org>>
> > Subject: Re: [ghc-steering-committee] #167: Deprecated Entities, rec: accept
> >  
> > Simon PJ argues for "value" over "data" as a specifier: https://github.com/ghc-proposals/ghc-proposals/pull/167#issuecomment-470947193 <https://github.com/ghc-proposals/ghc-proposals/pull/167#issuecomment-470947193>
> >  
> > I'm fine with this choice either (and I'm satisfied with the argument that deprecating or setting fixity for value "value" is a rare case to be considered seriously). If you have another opinion, please, speak up.
> >  
> > Vitaly
> >  
> > On Fri, Mar 8, 2019 at 11:42 AM Simon Peyton Jones <simonpj at microsoft.com <mailto:simonpj at microsoft.com>> wrote:
> > > I’ve made a post on the proposal thread asking why we don’t just follow the already-adopted proposal for WARNING and infix pragmas.
> > >  
> > > Simon
> > >  
> > > From: ghc-steering-committee <ghc-steering-committee-bounces at haskell.org <mailto:ghc-steering-committee-bounces at haskell.org>> On Behalf Of Simon Marlow
> > > Sent: 08 March 2019 07:57
> > > To: Vitaly Bragilevsky <bravit111 at gmail.com <mailto:bravit111 at gmail.com>>
> > > Cc: ghc-steering-committee <ghc-steering-committee at haskell.org <mailto:ghc-steering-committee at haskell.org>>
> > > Subject: Re: [ghc-steering-committee] #167: Deprecated Entities, rec: accept
> > >  
> > > Yes, I think this is the right way to go.
> > >  
> > > Cheers
> > > Simon
> > >  
> > > On Fri, 8 Mar 2019 at 05:25, Vitaly Bragilevsky <bravit111 at gmail.com <mailto:bravit111 at gmail.com>> wrote:
> > > > Hi everyone, 
> > > >  
> > > > I was asked to shepherd the proposal #167 (Deprecated Entities, https://github.com/nineonine/ghc-proposals/blob/depr-entities/proposals/0000-deprecated-entities.rst <https://github.com/nineonine/ghc-proposals/blob/depr-entities/proposals/0000-deprecated-entities.rst>). It is proposed to extend (nonpositional) DEPRECATED pragma with the two specifiers to disambiguate deprecating named type-level and value-level things. In its current formulation, the proposal suggests to use the specifiers "type" for type-level things and "pattern" for value-level things as follows:
> > > > 
> > > > data Bar = Bar
> > > > {-# DEPRECATED type Bar "Don't use type Bar" #-} 
> > > > data Baz = Baz
> > > > {-# DEPRECATED pattern Baz "Don't use data constructor Baz" #-}
> > > > 
> > > > Using this pragma without specifiers should mean deprecating both (as is works now).
> > > >  
> > > > After discussing this proposal within the committee (see https://mail.haskell.org/pipermail/ghc-steering-committee/2019-February/000894.html <https://mail.haskell.org/pipermail/ghc-steering-committee/2019-February/000894.html>), I recommend acceptance with one change, namely using "data" instead of "pattern" for deprecating value-level things. 
> > > >  
> > > > Reasons for choosing "data":
> > > > * it's a reserved keyword (as opposed to "value", which is another option)
> > > > * we are deprecating data constructors here
> > > > * it just feels right (sorry!)
> > > >  
> > > > Reasons against "data":
> > > > * it can be confusing whether we mean data type or data constructor
> > > > * we use "value" and "pattern" in other places meaning basically the same thing
> > > >  
> > > > If the committee decides to go this way, then the wider community may think about other proposals, such as
> > > > * adding positional DEPRECATED pragmas (including class instances deprecation)
> > > > * fixing inconsistencies with the fixity declarations (https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0008-type-infix.rst <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0008-type-infix.rst>) and updating ExplicitNamespaces in import/export lists
> > > > * deprecating usage of nonpositional DEPRECATED pragma without the specifiers
> > > >  
> > > > Silence is understood as agreement. 
> > > >  
> > > > Regards, 
> > > > Vitaly
> > > > 
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> > 
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> -- 
> Joachim Breitner
>   mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>
>   http://www.joachim-breitner.de/ <http://www.joachim-breitner.de/>
> 
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