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

On Mon, 11 Mar 2019 at 13:26, Richard Eisenberg wrote:

"value" would not work as the namespace indicator I envision for the future, as it's a commonly used variable name. (I would advocate against making it a keyword for this reason.) This knob is relatively easy to turn, though, so it's conceivable to use "value" today, and then if/when we start using "data" in the future, allow the use of "data" where we use "value", eventually deprecating and removing "value". It's a bit annoying to users to keep changing it, but only a bit. I've been in this game long enough to know that the future isn't quite predictable, and so I see the sense in choosing the best thing for us now, leaving the door open to fixing it later if necessary. I still advocate for "data", but I won't burst into tears if we choose "value".

I could see waiting a day or two for further commentary and then putting it to a committee vote. In the end, I think this choice matters little.

For those who (like me) might have been a bit confused about the current state of things: - There are 5 places that we want namespace specifiers now (possibly more later): import, export, fixity, WARNING, DEPRECATED - GHC's existing *ExplicitNamespaces* option allows *type* and *pattern* keywords to be used in import, export - The earlier proposal Require namespacing fixity declarations for type names and WARNING/DEPRECATED pragmas https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0008-ty... was accepted, and allows *type* and *value* keywords in fixity, WARNING, DEPRECATED - This proposal Deprecated Entities https://github.com/nineonine/ghc-proposals/blob/depr-entities/proposals/0000... suggests adding *type* and *pattern* specifiers to DEPRECATED pragmas. (note that DEPRECATED pragmas were covered by the earlier proposal, so this conflicts) - Vitaly's suggested modification of this proposal is to adopt *type* and *data* instead (for DEPRECATED pragmas), while Simon pointed out that we already accepted a proposal for this, using *type* and *value*, and that whatever we do we should do it consistently across import, export, fixity, WARNING, DEPRECATED (yes!) I don't think it makes a lot of sense to accept this proposal, since it conflicts with the earlier one. Should we instead work on a modification of the earlier proposal to extend it to import/export lists, and also resolve the debate about *data/pattern/value*? Richard's concerns about future extensions to add namespacing in expressions seem valid to me, it would be unfortunate to use *value* now if that will cause problems later. Cheers Simon

Richard

On Mar 11, 2019, at 9:12 AM, Vitaly Bragilevsky wrote:

Hi Richard,

Do you think that using "value" now is a real stopper for the future you are talking about? Maybe we should start thinking about making "value" a reserved keyword because it suits our purposes best as a namespace specifier. It looks like this data/value debate is the only issue before reaching the consensus on this proposal. So we have to do something about it.

Regards, Vitaly

On Sun, Mar 10, 2019 at 12:10 AM Richard Eisenberg wrote:

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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 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 wrote:

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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

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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 Sent: 08 March 2019 14:44 To: Simon Peyton Jones Cc: Simon Marlow ; ghc-steering-committee < ghc-steering-committee@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-4709471...

I'm fine with this choice either (and I'm satisfied with the argument

Am Freitag, den 08.03.2019, 14:46 +0000 schrieb Simon Peyton Jones via ghc-steering-committee: that deprecating or setting fixity for value "value" is a rare case to be considered seriously). If you have another opinion, please, speak up.

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Vitaly

On Fri, Mar 8, 2019 at 11:42 AM Simon Peyton Jones <

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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@haskell.org> On Behalf Of Simon Marlow Sent: 08 March 2019 07:57 To: Vitaly Bragilevsky Cc: ghc-steering-committee 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 wrote:

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Hi everyone,

I was asked to shepherd the proposal #167 (Deprecated Entities, https://github.com/nineonine/ghc-proposals/blob/depr-entities/proposals/0000...). It is proposed to extend (nonpositional) DEPRECATED pragma with the two specifiers to disambiguate deprecating named type-level and value-level

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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).

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After discussing this proposal within the committee (see

https://mail.haskell.org/pipermail/ghc-steering-committee/2019-February/0008...), I recommend acceptance with one change, namely using "data" instead of "pattern" for deprecating value-level things.

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Reasons for choosing "data": * it's a reserved keyword (as opposed to "value", which is another

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* 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

simonpj@microsoft.com> wrote: 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: option) the same thing

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If the committee decides to go this way, then the wider community

may think about other proposals, such as

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* 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-ty...) 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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