Hello Mario et al., On Tue, Dec 18, 2018 at 4:17 AM Mario Blažević wrote:

While you're reviewing AMP, please take a bit of time to also comment on the related new MonadPlus excise proposal at https://github.com/haskell/rfcs/pull/23

The proposal is very short so it should be an easy decision. Thank you.

As I've explained already on the RFC, I refuse (i.e. to make this very clear: I'm exercising my veto) to accept the AMP change without also at least a commitment to MFP and MRP. And note that the committee was created with the explicit request from SPJ that it ought to be a consensus-based decision process rather than a democratic voting process -- and there isn't consensus in this matter as far as I'm concerned. The discussion started on the right foot with Richard rightly saying

The redundant functions (like return) are all well and good in an implementation such as GHC, but I think they should be struck from the Report. Let's design it like we should have from the beginning, cleanly. GHC could then include its non-conformance with this new standard as an infelicity. Perhaps GHC can even deprecate return, but I don't have a problem with just living with the infelicity.

That's the ideal we should strive for and what I expected the discussion to follow-through but unfortunately it got lost along the way. Herbert

On 18/12/2018 12:23, Henrik Nilsson wrote:

Hi all,

Well, I am in favour of discussing AMP and MRP separately

Whoops, my bad, wasn't familiar enough to realise my suggestion was effectively covered by MRP! I think it might be a legitimate thing to tease do-uses-*> apart from MRP-as-a-whole as it only affects do notation and is already justifiable in terms of AMP's rationale alone, but I'll entirely understand if it's a bigger can of worms than is worth it at this point. That said, if there's any appetite for it we could ask for the relevant toggles to be added to GHC and gather some data, possibly branching this off as an AMP-or-MRP thing? As I've said, I have a use case for it today and in the absence of other extensions or alterations. It's a lot easier to estimate ecosystem impact given a switch that'll find all the resulting errors and give everyone a chance to fail any tests.

On 18/12/2018 13:41, Henrik Nilsson wrote:

Hi,

Philippa wrote:

...

It's a lot easier to estimate ecosystem impact given a switch that'll find all the resulting errors and give everyone a chance to fail any tests.

Yes, a good point.

But just to be clear, the impact of some changes go well beyond what can be assessed by looking at impact on an existing code base alone. And that is one reason for why MRP has been, and remains, so controversial.

Sure. I think the one conceptual shift do-uses-*> would create is that do notation no longer (except in the degenerate tail case) always brings a Monad constraint, instead it would bring Applicative unless something is bound with <-. If I'm right then that's certainly a long way short of MRP per se, which I'm not interested in discussing at this point :) I'm not sure how much of a problem that would create for teachers - I imagine it depends very much on one's style, as it can even reinforce the idea that Monad is partly about (unconstrained) binding! Which is a plus if you like making the connection to ANF to some extent and letting people think about a family of machine models. I think that's something it might even be nice to let students play with in some circumstances? Though I've done all my teaching 1:1 or with very small groups myself and generally not to first year undergraduates. Nor have I seen how AMP is affecting teaching in general properly. Certainly something I'd be happy to talk about more if and when there's time - realistically there's no good reason to hold up AMP over this when it could be treated as a third proposal which depends on AMP and which MRP mandates. Should I find a TLA for it? Is there somewhere else I should be pasting my thoughts here to? Any other comments? If I'm wasting people's time I'd rather stop, but if this is a viable proposal refactoring that might be another matter. Cheers, Philippa

On 2018-12-18 2:38 a.m., Herbert Valerio Riedel wrote:

Hello Mario et al.,

On Tue, Dec 18, 2018 at 4:17 AM Mario Blažević wrote:

...

While you're reviewing AMP, please take a bit of time to also comment on the related new MonadPlus excise proposal at https://github.com/haskell/rfcs/pull/23

The proposal is very short so it should be an easy decision. Thank you.

As I've explained already on the RFC, I refuse (i.e. to make this very clear: I'm exercising my veto) to accept the AMP change without also at least a commitment to MFP and MRP. And note that the committee was created with the explicit request from SPJ that it ought to be a consensus-based decision process rather than a democratic voting process -- and there isn't consensus in this matter as far as I'm concerned.

What exactly would you consider "a commitment to MFP and MRP"? As for myself, they are both on my to-do list. I just don't want to get lost in endless discussions without having anything done, so I performed the first step, the AMP. If that is accepted, I fully intend to prepare both MFP and MRP proposals - unless somebody else does it first. Is that commitment enough?

Getting to ditch a similar connotation in do notation is exactly why I've started this thread, of course! Some instances are far less about having pure/return, at least without some more powerful constructs we can't have in a standardised Haskell just yet. It's maybe a personal irritation that ApplicativeDo outright fails in that situation. I was slightly appalled when I realised just now what pronunciations of *> and <* I could most easily justify if nobody else comes up with a suggestion - I think <* might be "klap". I do think there's value in wondering whether there are small changes to GHC we might request if nobody else does it. But that's partly because the Report has to be descriptive by default - otherwise there's no good institutional eye on neatening things up over time that has an eye on standards rather than the concerns that drive GHC. Fundamentally, if I'd wanted to drag up MRP rather than round off an edge, I would've done so explicitly! If someone wants to tell me where to nag the GHC folks I guess I might find the time. But I'm definitely looking at removing warts in the context of things that are already happening myself. On 18/12/2018 14:52, Cale Gibbard wrote:

Is it just me, or is all the discussion in these threads much more easily resolved if the Report is simply a report? Describe what is, rather than what you wish it was, and there's much less room for disagreement. A future Report can describe the way that these things work differently in the future when the changes actually happen in the implementation(s).

I don't know about anyone else, but at least from my perspective the value of the Report is in being valid documentation. The extent to which it fails to describe the actual family of languages we're presently writing code in is the extent to which it is failing to be a useful resource for our daily lives.

I dunno, I feel kind of strange when people talk about removing 'return' for example, since it's very unlikely to go anywhere any time soon given how much code it is referenced in. It would be practically unreasonable even to try to deprecate it. Given that the Report is going to discuss this part of the language, it makes sense that it should be documented.

Secondarily, it's a bit hard to describe why this is, but I personally find it a bit obnoxious whenever someone uses 'pure' rather than 'return' if the functor is known to be an instance of Monad and the generality isn't needed. It's a kind of signal that the code we're writing is (and perhaps needs to be) Applicative-polymorphic, or that we lack a Monad instance. So when I see it, I'm forced to consider for a moment why that might be, and whether I've understood the context incorrectly (and if it's not the case, that's sort of irritating).

So when I see a suggestion to remove 'return' altogether it's sort of like "let's make everything mildly annoying to read forever" (by forcing this thought about exactly how general the code is, and making it slightly harder to guess the types at a glance).

It's like while pure and return are equal whenever they would both typecheck, they've come to have very different connotations about the surrounding code.

On Tue, Dec 18, 2018, 05:42 Philippa Cowderoy, mailto:flippa@flippac.org> wrote:

I'm having a moment of fail trying to work out how to leave a comment.

Is there a reason (other than GHC not doing it yet) not to have do notation use *> instead of >> in line with using the least restrictive function? I have some otherwise-nice logic programming code that would actively benefit from it and it seems like a missing step from here.

On 15/12/2018 23:46, Mario Blažević wrote: > The very first RFC created (https://github.com/haskell/rfcs/pull/1), > the Applicative/Monad Proposal, has now reached the Last Call stage. > In order to ground the discussion, I have taken some time to update > the Prelude and the text of the Haskell Report with its effects before > the call. The rendered report is available at > https://github.com/blamario/rfcs/blob/amp/report/report/haskell.pdf > for your review. > > > TL;DR: > > The proposed changes to the report add the latest design of the > Applicative and Alternative classes, but otherwise are intentionally > minimal. Any further modifications, like the MonadFail proposal or > moving return out of the Monad class, should be relegated to new RFCs. > > > In some more detail, the changes are: > > 1. Applicative has been added as a subclass of Functor and superclass > of Monad, its methods and laws as currently defined in the base > library. The class and all its methods (pure, (<*>), (<*), (*>), and > liftA2) are exported from Prelude, but no other Applicative-related > functions (like liftA3) are. > > 2. The Functor class definition has been moved from module > Control.Monad to Control.Applicative in order to avoid circular > imports. Note that neither module is a part of the language > specification. > > 3. The Monad class has been left unmodified, apart from making > Applicative its superclass and adding  return a == pure a  as a law. > > 4. Alternative has been added to the Control.Applicative module, but > not to Prelude. This is the same treatment already meted to MonadPlus. > I'm unsure why MonadPlus even exists in the report, as it has no > relevance to the language specification, and I would gladly remove > both classes. > > > Please take some time within the following three weeks (including some > extra allowance for the upcoming holiday breaks) to vote for or > against the proposal, or to leave a comment with suggestions for its > improvement. > > > _______________________________________________ > Haskell-prime mailing list > Haskell-prime@haskell.org mailto:Haskell-prime@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org mailto:Haskell-prime@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime

Not taken personally, don't worry. You've done enough picking up where I've failed to get work done over the years, too! I'm trying to be deliberate about "this does raise this issue but it isn't a blocker and can be separated out" pretty much precisely so I can be cheerfully ignored if nobody else cares. I may have tweeted some minor irritation about how when it comes to my code, ApplicativeDo fails to give a, er, *> though :) <$ could reasonably be rebound to |- in some of my code, and the main reason I don't is I'm using it to implement a type system which has its own turnstile. Which I'm pretty sure I told you years ago, but it may be mildly new to others here. On 18/12/2018 15:15, Cale Gibbard wrote:

I guess I didn't mean to pick on your suggestion exactly -- the comments on the pull request triggered my remark even moreso, but I was on my phone and it was slightly easier to reply here.

Where I work, we've come to calling <$ "ice cream cone", so perhaps <* is "snow cone", lol.

It's definitely valuable to think about and discuss where the language might go, but every time I see that discussion in the context of producing the Haskell Report, I think about how H2010 went almost nowhere because of how this kind of discussion makes it easy to not decide on what any particular change to the Report might be, and sort of wish that we had a Report which was current at all...

On Tue, 18 Dec 2018 at 10:07 Philippa Cowderoy mailto:flippa@flippac.org> wrote:

Getting to ditch a similar connotation in do notation is exactly why I've started this thread, of course! Some instances are far less about having pure/return, at least without some more powerful constructs we can't have in a standardised Haskell just yet. It's maybe a personal irritation that ApplicativeDo outright fails in that situation.

I was slightly appalled when I realised just now what pronunciations of *> and <* I could most easily justify if nobody else comes up with a suggestion - I think <* might be "klap".

I do think there's value in wondering whether there are small changes to GHC we might request if nobody else does it. But that's partly because the Report has to be descriptive by default - otherwise there's no good institutional eye on neatening things up over time that has an eye on standards rather than the concerns that drive GHC.

Fundamentally, if I'd wanted to drag up MRP rather than round off an edge, I would've done so explicitly! If someone wants to tell me where to nag the GHC folks I guess I might find the time. But I'm definitely looking at removing warts in the context of things that are already happening myself.

On 18/12/2018 14:52, Cale Gibbard wrote:

...

Is it just me, or is all the discussion in these threads much more easily resolved if the Report is simply a report? Describe what is, rather than what you wish it was, and there's much less room for disagreement. A future Report can describe the way that these things work differently in the future when the changes actually happen in the implementation(s).

I don't know about anyone else, but at least from my perspective the value of the Report is in being valid documentation. The extent to which it fails to describe the actual family of languages we're presently writing code in is the extent to which it is failing to be a useful resource for our daily lives.

I dunno, I feel kind of strange when people talk about removing 'return' for example, since it's very unlikely to go anywhere any time soon given how much code it is referenced in. It would be practically unreasonable even to try to deprecate it. Given that the Report is going to discuss this part of the language, it makes sense that it should be documented.

Secondarily, it's a bit hard to describe why this is, but I personally find it a bit obnoxious whenever someone uses 'pure' rather than 'return' if the functor is known to be an instance of Monad and the generality isn't needed. It's a kind of signal that the code we're writing is (and perhaps needs to be) Applicative-polymorphic, or that we lack a Monad instance. So when I see it, I'm forced to consider for a moment why that might be, and whether I've understood the context incorrectly (and if it's not the case, that's sort of irritating).

So when I see a suggestion to remove 'return' altogether it's sort of like "let's make everything mildly annoying to read forever" (by forcing this thought about exactly how general the code is, and making it slightly harder to guess the types at a glance).

It's like while pure and return are equal whenever they would both typecheck, they've come to have very different connotations about the surrounding code.

On Tue, Dec 18, 2018, 05:42 Philippa Cowderoy, mailto:flippa@flippac.org> wrote:

I'm having a moment of fail trying to work out how to leave a comment.

Is there a reason (other than GHC not doing it yet) not to have do notation use *> instead of >> in line with using the least restrictive function? I have some otherwise-nice logic programming code that would actively benefit from it and it seems like a missing step from here.

On 15/12/2018 23:46, Mario Blažević wrote: > The very first RFC created (https://github.com/haskell/rfcs/pull/1), > the Applicative/Monad Proposal, has now reached the Last Call stage. > In order to ground the discussion, I have taken some time to update > the Prelude and the text of the Haskell Report with its effects before > the call. The rendered report is available at > https://github.com/blamario/rfcs/blob/amp/report/report/haskell.pdf

> for your review. > > > TL;DR: > > The proposed changes to the report add the latest design of the > Applicative and Alternative classes, but otherwise are intentionally > minimal. Any further modifications, like the MonadFail proposal or > moving return out of the Monad class, should be relegated to new RFCs. > > > In some more detail, the changes are: > > 1. Applicative has been added as a subclass of Functor and superclass > of Monad, its methods and laws as currently defined in the base > library. The class and all its methods (pure, (<*>), (<*), (*>), and > liftA2) are exported from Prelude, but no other Applicative-related > functions (like liftA3) are. > > 2. The Functor class definition has been moved from module > Control.Monad to Control.Applicative in order to avoid circular > imports. Note that neither module is a part of the language > specification. > > 3. The Monad class has been left unmodified, apart from making > Applicative its superclass and adding  return a == pure a  as a law. > > 4. Alternative has been added to the Control.Applicative module, but > not to Prelude. This is the same treatment already meted to MonadPlus. > I'm unsure why MonadPlus even exists in the report, as it has no > relevance to the language specification, and I would gladly remove > both classes. > > > Please take some time within the following three weeks (including some > extra allowance for the upcoming holiday breaks) to vote for or > against the proposal, or to leave a comment with suggestions for its > improvement. > > > _______________________________________________ > Haskell-prime mailing list > Haskell-prime@haskell.org mailto:Haskell-prime@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org mailto:Haskell-prime@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime

On 18/12/2018 18:02, Henrik Nilsson wrote:

Moreover, while there is little risk of confusion when arrow syntax is used, looking just at names, the fact is that the use of the distinct "returnA" also sends a similar signal to the reader, and consequently there is a certain consistency in distinct names being used for the three different computational notions for which (variations of) do-notation is provided.

I'm reminded that once upon a time I suggested what we now call ApplicativeDo start off with its own keyword for specifically Applicative code and that what it now tries to do might be possible! The lexical bikeshedding doesn't strike me as fun though.

Is there information anywhere on the process for acceptance/rejection criteria. It sounds like hvr can outright reject any proposal - are there others with that power? What is generally required for acceptance? Not meant critically, just interested On Wed, 16 Jan 2019, 8:01 pm Mario Blažević

A month passed since the last call, and I'm sorry to say that the Applicative/Monad proposal has been rejected. Herbert has vetoed it on the grounds that it doesn't come packaged with MonadFail and MonadOfNoReturn proposals.

This is very unfortunate because (I thought) there was finally a glimmer of hope for Haskell 2020. The new process used to complete the RelaxedPolyRec proposal seemed promising, as it worked around the commitee's letargy problem. As it turns out, that wasn't the only problem.

In all fairness, Herbert did state [1] he intends to write up the combination of AMP, MFP, and MNRP the way he likes it. I do hope that happens, but when and if he submits the combined proposal, I would not be surprised if, for example, Philippa should veto it on the grounds that it doesn't include the ApplicativeDo proposal that she's been vocal about. This committee is a far cry from the one that gave us Haskell '98.

A Haskell 2020 report with no AMP would be pointless, in my opinion, so I'm going to suspend my work on the report until this issue is resolved. I still think the best course of action may be to disband the current disfunctional committee and form a new one, as I proposed [2] before establishing the new process.

[1] https://github.com/haskell/rfcs/pull/1#issuecomment-448126690 [2] https://mail.haskell.org/pipermail/haskell-prime/2018-October/004370.html

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I'm not committee, so I don't need to be part of any consensus. Myself I wouldn't bundle something I want up with something that's needed just to get it to pass anyway, for what it's worth. I'd rather keep my own ideas modular enough they don't bog anything down! So if I try to push my pet feature further it'll be its own proposal and I for one can't tie it to anything. But I certainly understand where you're coming from on this. I'm sorry if I've made things harder for you here, and I have to admit I had preferred that MFP and MNR wait their turn. I'm hoping that one way or another, Herbert's proposal means we reach some kind of conclusion in the long run - at the least, we will have two mutually-exclusive proposals on the table and an obligation to pick one, refine quickly or go home. I'd like to thank you for your work - myself I'm infamously unable to get things done (to the point of unemployability), and I've stayed off the committee precisely because I can appreciate the effort involved. On 16/01/2019 20:00, Mario Blažević wrote:

A month passed since the last call, and I'm sorry to say that the Applicative/Monad proposal has been rejected. Herbert has vetoed it on the grounds that it doesn't come packaged with MonadFail and MonadOfNoReturn proposals.

This is very unfortunate because (I thought) there was finally a glimmer of hope for Haskell 2020. The new process used to complete the RelaxedPolyRec proposal seemed promising, as it worked around the commitee's letargy problem. As it turns out, that wasn't the only problem.

In all fairness, Herbert did state [1] he intends to write up the combination of AMP, MFP, and MNRP the way he likes it. I do hope that happens, but when and if he submits the combined proposal, I would not be surprised if, for example, Philippa should veto it on the grounds that it doesn't include the ApplicativeDo proposal that she's been vocal about. This committee is a far cry from the one that gave us Haskell '98.

A Haskell 2020 report with no AMP would be pointless, in my opinion, so I'm going to suspend my work on the report until this issue is resolved. I still think the best course of action may be to disband the current disfunctional committee and form a new one, as I proposed [2] before establishing the new process.

[1] https://github.com/haskell/rfcs/pull/1#issuecomment-448126690 [2] https://mail.haskell.org/pipermail/haskell-prime/2018-October/004370.html

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On 17/01/2019 16:46, Mario Blažević wrote:

On 2019-01-16 3:26 p.m., Philippa Cowderoy wrote:

...

... I'd like to thank you for your work - myself I'm infamously unable to get things done (to the point of unemployability), and I've stayed off the committee precisely because I can appreciate the effort involved.

    Apologies, for some reason I thought you were on the committee. Your self-description sounds like you'd fit right in.

I couldn't possibly comment! I'll admit it's left me with an eye for small-but-significant changes though. A lot of my wider involvement with the community has been of a more "social" nature, including my stint as Anglohaskell's meta-organiser and sometimes organiser, though I also mentored the Summer of Code project that got Parsec 3 off the ground once upon a time too. Thinking about it, that one does suggest I may have a talent for causing inevitable yet untold chaos! Perhaps that made it inevitable that someone would invite me onto this list in the dim and distant past? -- Philippa

Somehow every time I see messages from this list I'm again tempted to suggest that it would all be so much easier if the goal were to document the language as it exists in a fixed, already-released version of GHC. But I'm not a member either. If I were, I'd pick a version and veto anything which wasn't in that GHC. You could even pick a really old version of GHC for this purpose and come out with a document that's far more relevant to Haskell users of today than the Haskell 2010 Report. Just getting the Report up to the point where it actually describes most of the stuff in GHC 6 would be fantastic progress, tbh. Also I'd strongly consider just dropping the specification of the Prelude altogether. I'm not sure it's even all that helpful to include it at this point, given that whatever version someone is using is always going to have Haddock documentation. It's both a point of contention, and of limited usefulness to document. On Sun, Mar 31, 2019, 12:02 Bardur Arantsson, wrote:

On 16/01/2019 21.00, Mario Blažević wrote:

...

In all fairness, Herbert did state [1] he intends to write up the combination of AMP, MFP, and MNRP the way he likes it.

Did anything come of this?

Regards,

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