Re: Breaking Changes and Long Term Support Haskell

[Geoffrey Mainland]

On 10/22/2015 02:25 PM, Edward Kmett wrote:
>
> On Thu, Oct 22, 2015 at 1:41 PM, Geoffrey Mainland
> > wrote:
>
> On 10/22/2015 01:29 PM, Edward Kmett wrote:
> > On Thu, Oct 22, 2015 at 12:59 PM, Geoffrey Mainland
> > 
> >> wrote:
> >
> >
> > I am not against changing the Prelude! But it sure would be
> nice if
> > -XHaskell98 gave me a Haskell 98 Prelude and -XHaskell2010
> gave me a
> > Haskell 2010 Prelude, both of which could be used with external
> > packages
> > that themselves used the more modern Prelude.
> >
> >
> > It would definitely be a preferable state of affairs. Unfortunately,
> > at least with the tools available to us today, such a plan is
> > incompatible with any plan that introduces a new superclass. It also
> > cuts off plans that ever factors an existing class into two, such as
> > the MonadFail proposals. We simply do not at this time have the
> > technical capabilities that would support such a system. If they
> > showed up in GHC we can adapt plans to fit.
>
> Great!
>
> Could we work to characterize what technical capabilities we would
> need
> to support full backwards Prelude compatibility?
>
> Here is my rough understanding of what we would need:
>
> 1) Some method for "default superclasses." This would solve the
> AMP issue.
>
> 2) A method for factoring existing classes into two (or more) parts.
> This would solve the MonadFail problem.
>
> 3) A method for imposing extra superclass constraints on a class. This
> would be needed for full Num compatibility. Seems much less important
> that 1 and 2.
>
> The most thought has gone into 1.
>
>
> Are these three technical capabilities *all* that we would need?
> Perhaps
> we also need a way to tie the current language (-XHaskell98,
> -XHaskell2010) to a particular implementation of the Prelude.
>
>  
> I don't have a concrete plan here. I'm not even sure one can be
> achieved that works. I'd say that the burden of figuring out such a
> thing falls on the party that can create a plan, pitch it to the
> community and potentially implement it.
>
> If I enumerate a set of conditions here I'm basically implying that
> I'd agree to any plan that incorporated them. I'm just not prepared to
> make that commitment sight-unseen to something with unknown warts and
> implications.
>
> I can, however, say that it is plausible that what you have enumerated
> above could potentially address the outstanding issues, but I don't
> know how good of a compromise the result would be. 
>
> -Edward

I don't have a concrete plan either, not am I sure that one is possible.
But I don't see how having a conversation about how one might achieve
backwards compatibility would commit anyone to anything. Any eventual
proposal would have to go through the same approval process as every
other proposal. And even if we did have a hypothetical draft proposal
that you had at some point stated you approved of in some way, you would
always be free to change your mind!

Isn't the libraries list exactly where this sort of conversation should
happen?

Cheers,
Geoff
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Re: Breaking Changes and Long Term Support Haskell

[Edward Kmett]

On Wed, Oct 21, 2015 at 8:42 PM, Gregory Collins 
wrote:

>
> On Wed, Oct 21, 2015 at 3:18 PM, Geoffrey Mainland 
> wrote:
>
>> My original email stated my underlying concern: we are losing valuable
>> members of the community not because of the technical decisions that are
>> being made, but because of the process by which they are being made.
>>
> [If] you're doing research you're on the treadmill, almost by definition,
> and you're delighted that we're finally making some rapid progress on
> fixing up some of the longstanding warts.
>
> If you're a practitioner, you are interested in using Haskell for, y'know,
> writing programs. You're probably in one of two camps: you're in "green
> field" mode writing a lot of new code (early stage startups, prototype
> work, etc), or you're maintaining/extending programs you've already written
> that are out "in the field" for you doing useful work. Laura Wingerd calls
> this the "annealing temperature" of software, and I think this is a nice
> metaphor to describe it. How tolerant you are of ecosystem churn depends on
> what your temperature is: and I think it should be obvious to everyone that
> Haskell having "success" for programming work would mean that lots of
> useful and correct programs get written, so everyone who is in the former
> camp will cool over time to join the latter.
>

I've made the point before and I don't really want to belabor it: our de
> facto collective posture towards breaking stuff, especially in the past few
> years, has been extremely permissive, and this alienates people who are
> maintaining working programs.
>

Even among people who purported to be teaching Haskell or using Haskell
today in industry the margin of preference for the concrete FTP proposal
was ~79%. This was considerably higher than I expected in two senses. One:
there were a lot more people who claimed to be in one of those two roles
than I expected by far, and two: their appetite for change was higher than
I expected. I initially expected to see a stronger "academic vs. industry"
split in the poll, but the groups were only distinguishable by a few
percentage point delta, so while I expected roughly the end percentage of
the poll, based on the year prior I'd spent running around the planet to
user group meetings and the like, I expected it mostly because I expected
more hobbyists and less support among industrialists.

>
I'm actually firmly of the belief that the existing committee doesn't
> really have process issues, and in fact, that often it's been pretty
> careful to minimize the impact of the changes it wants to make. As others
> have pointed out, lots of the churn actually comes from platform libraries,
> which are out of the purview of this group.
>

Historically we've had a bit of a split personality on this front. Nothing
that touches the Prelude had changed in 17 years. On the other hand the
platform libraries had maintained a pretty heavy rolling wave of breakage
the entire time I've been around in the community. On a more experimental
feature front, I've lost count of the number of different things we've done
to Typeable or template-haskell.


> All I'm saying is that if we want to appeal to or cater to working
> software engineers, we have to be a lot less cavalier about causing more
> work for them, and we need to prize stability of the core infrastructure
> more highly. That'd be a broader cultural change, and that goes beyond
> process: it's policy.
>

The way things are shaping up, we've had 17 years of rock solid stability,
1 release that incorporated changes that were designed to minimize impact,
to the point that the majority of the objections against them are of the
form where people would prefer that we broke _more_ code, to get a more
sensible state. Going forward, it looks like the next 2 GHC releases will
have basically nothing affecting the Prelude, and there will be another
punctuation in the equilibrium around 8.4 as the next set of changes kicks
in over 8.4 and 8.6 That gives 2 years worth of advance notice of pending
changes, and a pretty strong guarantee from the committee that you should
be able to maintain code with a 3 release window without running afoul of
warnings or needing CPP.

So, out of curiosity, what additional stability policy is it that you seek?

-Edward
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Re: Breaking Changes and Long Term Support Haskell

[Taru Karttunen]

On 21.10 17:42, Gregory Collins wrote:
> All I'm saying is that if we want to appeal to or cater to working software
> engineers, we have to be a lot less cavalier about causing more work for
> them, and we need to prize stability of the core infrastructure more
> highly. That'd be a broader cultural change, and that goes beyond process:
> it's policy.

I think that how the changes are handled can make a large difference.

E.g. if

A) Most of Hackage (including dependencies) compiles with new GHC.
(stack & stackage helps somewhat)

B) There is an automated tool that can be used to fix most code
to compile with new versions of GHC without warnings or CPP.

C) Hackage displays vocally what works with which versions of
GHC (Status reports do help somewhat)

Then I think much of the complaints would go away.

- Taru Karttunen
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Re: Breaking Changes and Long Term Support Haskell

[Herbert Valerio Riedel]

On 2015-10-22 at 08:04:10 +0200, Taru Karttunen wrote:

[...]

> B) There is an automated tool that can be used to fix most code
> to compile with new versions of GHC without warnings or CPP.

Fyi, Alan is currently working on levaraging HaRe[1] in

 https://github.com/alanz/Hs2010To201x (the `parsing-only` branch)

and it's already showing great promise. However, tools like this will
only be able to handle the no-brainer cases, as in general it's a NP
hard problem. But luckily, those boring mechanical refactorings usually
represent the vast majority, and that's the tedious work we want
tooling to assist us most with.


> C) Hackage displays vocally what works with which versions of
> GHC (Status reports do help somewhat)


I.e. something like

  http://matrix.hackage.haskell.org/package/text

? :-)


 [1]: Btw, here's a recent talk which also mentions the use-case of using
  HaRe to update between Haskell Report revisions or `base` versions:
 
  
https://skillsmatter.com/skillscasts/6539-a-new-foundation-for-refactoring-ghc-exactprint
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Re: Breaking Changes and Long Term Support Haskell

[Edward Kmett]

On Thu, Oct 22, 2015 at 2:04 AM, Taru Karttunen  wrote:

> E.g. if
>
> A) Most of Hackage (including dependencies) compiles with new GHC.
> (stack & stackage helps somewhat)
>
> B) There is an automated tool that can be used to fix most code
> to compile with new versions of GHC without warnings or CPP.
>
> C) Hackage displays vocally what works with which versions of
> GHC (Status reports do help somewhat)
>


> Then I think much of the complaints would go away.


If we had those things, indeed they would!

However, beyond A (GHC 7.10 was tested more extensively against
hackage/stackage than any previous release of Haskell by far!), the others
require various degrees of engineering effort, including some way to deal
with refactoring code that already has CPP in it, more extensive build-bot
services, etc. and those sort of non-trivial artifacts just haven't been
forthcoming. =/

I would be very happy if those things showed up, however.

-Edward
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RE: Breaking Changes and Long Term Support Haskell

[Simon Peyton Jones]

| > Are these three technical capabilities *all* that we would need?
| > Perhaps
| > we also need a way to tie the current language (-XHaskell98,
| > -XHaskell2010) to a particular implementation of the Prelude.
| >
| >
| > I don't have a concrete plan here. I'm not even sure one can be
| > achieved that works. I'd say that the burden of figuring out such a
| > thing falls on the party that can create a plan, pitch it to the
| > community and potentially implement it.

In fact there is more than one concrete plan: 
https://ghc.haskell.org/trac/ghc/wiki/IntrinsicSuperclasses

All are complex, only partially designed, entirely unimplemented (and the 
implementation will be non-trivial), and lacking an active champion.  The one I 
link to above is probably the leading contender, but it feels too complicated 
to me.

Simon

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Re: Breaking Changes and Long Term Support Haskell

[Edward Kmett]

On Thu, Oct 22, 2015 at 1:37 PM, Gregory Collins 
wrote:

>
> On Wed, Oct 21, 2015 at 11:40 PM, Edward Kmett  wrote:
>
>> All I'm saying is that if we want to appeal to or cater to working
>>> software engineers, we have to be a lot less cavalier about causing more
>>> work for them, and we need to prize stability of the core infrastructure
>>> more highly. That'd be a broader cultural change, and that goes beyond
>>> process: it's policy.
>>>
>>
>> The way things are shaping up, we've had 17 years of rock solid stability
>>
>
> I have >95% confidence that all of the C++ programs I wrote 15 years ago
> would build and work if I dusted them off and typed "make" today. I have
> Haskell programs I wrote last year that I probably couldn't say that about.
>
> So I don't buy that, at all, at least if we're discussing the topic of the
> stability of the core infrastructure in general rather than changes being
> made to the Prelude. It's been possible to write to Haskell 98 without too
> much breakage, yes, but almost nobody actually does that; they write to
> Haskell as defined by GHC + the boot libraries + Haskell platform +
> Hackage, IMO with decreasing expectations of stability for each. The core
> set breaks a lot.
>

I definitely agree here.

We have a lot of libraries in the Haskell Platform that have fairly liberal
change policies. On the other hand, we have a policy of "maintainer
decides" around issues. This yields a fairly decentralized change
management process, with different maintainers who have different views.
The Platform gives us a central pool of packages that are generally the
"best of breed" in their respective spaces, but gives us few stability
guarantees.

Heck, every release I wind up having to change whatever code I have that
uses template-haskell or Typeable.

On the other hand, it isn't clear with a larger "core" platform with harder
stability guarantees that we have a volunteer force that can and would sign
up for the long slog of maintenance without that level of autonomy.


> We definitely shouldn't adopt a posture to breaking changes as
> conservative as the C++ committee's, and literally nobody in the Haskell
> community is arguing against breaking changes in general, but as I've
> pointed out, most of these breakages could have been avoided with more
> careful engineering, and indeed, on many occasions the argument has been
> made and it's fallen on deaf ears.
>

I would argue that there are individual maintainers that give lie to that
statement. In many ways Johan himself has served as a counter-example
there. The libraries he has maintained have acted as a form of bedrock with
long maintenance windows. On the other hand, the burden of maintaining that
stability seems to have ultimately burned him out.

They can speak for themselves but I think for Mark and Johan, this is a
> "straw that broke the camel's back" issue rather than anything to do with
> the merits of removing return from Monad. I think the blowback just happens
> to be so much stronger on MRP because the breaking change is so close to
> the core of the language, and the benefits are so nebulous. fixing an
> aesthetic problem has almost zero practical value
>

I personally don't care about the return side of the equation.

Herbert's MRP proposal was an attempt by him to finish out the changes
started by AMP so that a future Haskell Report can read cleanly. Past
reports have been remarkably free of historical baggage.

I'd personally readily sacrifice "progress" there in the interest of
harmony. Herbert as haskell-prime chair possibly feels differently.


> and ">> could be slightly more efficient for some monads" is pretty weak
> sauce.
>

The issue right now around (>>) is that it has knock-on effects that run
pretty far and wide. "Weak sauce" or not, it means through second order
consequences that we can't move the useless mapM and sequence to the top
level from their current status as memberrs of Traversable and that users
have to care about which of two provably equivalent things that they are
using, at all times.

It means that code that calls mapM will be less efficient and that mapM_
behaves in a manner with rather radically different space and time behavior
than mapM today and not in a consistently good way.

-Edward
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Re: Breaking Changes and Long Term Support Haskell

[Taru Karttunen]

On 22.10 09:04, Herbert Valerio Riedel wrote:
> Fyi, Alan is currently working on levaraging HaRe[1] in
> 
>  https://github.com/alanz/Hs2010To201x (the `parsing-only` branch)
> 
> and it's already showing great promise. However, tools like this will
> only be able to handle the no-brainer cases, as in general it's a NP
> hard problem. But luckily, those boring mechanical refactorings usually
> represent the vast majority, and that's the tedious work we want
> tooling to assist us most with.

Yes, getting it 99% there as an automated tool would be enough
for most cases.


> > C) Hackage displays vocally what works with which versions of
> > GHC (Status reports do help somewhat)
> 
> 
> I.e. something like
> 
>   http://matrix.hackage.haskell.org/package/text

Yes! Is there a reason that it is not displayed on
http://hackage.haskell.org/package/text which only
displays a link to Status of a 7.8.3 build?

How many percent of Hackage is built with matrix.h.h.o
and is there a plan to integrate it into Hackage pages?

- Taru Karttunen
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Re: Breaking Changes and Long Term Support Haskell

[Geoffrey Mainland]

On 10/22/2015 02:40 AM, Edward Kmett wrote:
> On Wed, Oct 21, 2015 at 8:42 PM, Gregory Collins
> > wrote:
>
>
> On Wed, Oct 21, 2015 at 3:18 PM, Geoffrey Mainland
> > wrote:
>
> My original email stated my underlying concern: we are losing
> valuable
> members of the community not because of the technical
> decisions that are
> being made, but because of the process by which they are being
> made.
>
> [If] you're doing research you're on the treadmill, almost by
> definition, and you're delighted that we're finally making some
> rapid progress on fixing up some of the longstanding warts.
>
> If you're a practitioner, you are interested in using Haskell for,
> y'know, writing programs. You're probably in one of two camps:
> you're in "green field" mode writing a lot of new code (early
> stage startups, prototype work, etc), or you're
> maintaining/extending programs you've already written that are out
> "in the field" for you doing useful work. Laura Wingerd calls this
> the "annealing temperature" of software, and I think this is a
> nice metaphor to describe it. How tolerant you are of ecosystem
> churn depends on what your temperature is: and I think it should
> be obvious to everyone that Haskell having "success" for
> programming work would mean that lots of useful and correct
> programs get written, so everyone who is in the former camp will
> cool over time to join the latter.
>
>
> I've made the point before and I don't really want to belabor it:
> our de facto collective posture towards breaking stuff, especially
> in the past few years, has been extremely permissive, and this
> alienates people who are maintaining working programs.
>
>
> Even among people who purported to be teaching Haskell or using
> Haskell today in industry the margin of preference for the concrete
> FTP proposal was ~79%. This was considerably higher than I expected in
> two senses. One: there were a lot more people who claimed to be in one
> of those two roles than I expected by far, and two: their appetite for
> change was higher than I expected. I initially expected to see a
> stronger "academic vs. industry" split in the poll, but the groups
> were only distinguishable by a few percentage point delta, so while I
> expected roughly the end percentage of the poll, based on the year
> prior I'd spent running around the planet to user group meetings and
> the like, I expected it mostly because I expected more hobbyists and
> less support among industrialists.
>
> I'm actually firmly of the belief that the existing committee
> doesn't really have process issues, and in fact, that often it's
> been pretty careful to minimize the impact of the changes it wants
> to make. As others have pointed out, lots of the churn actually
> comes from platform libraries, which are out of the purview of
> this group.
>
>
> Historically we've had a bit of a split personality on this front.
> Nothing that touches the Prelude had changed in 17 years. On the other
> hand the platform libraries had maintained a pretty heavy rolling wave
> of breakage the entire time I've been around in the community. On a
> more experimental feature front, I've lost count of the number of
> different things we've done to Typeable or template-haskell.
>  
>
> All I'm saying is that if we want to appeal to or cater to working
> software engineers, we have to be a lot less cavalier about
> causing more work for them, and we need to prize stability of the
> core infrastructure more highly. That'd be a broader cultural
> change, and that goes beyond process: it's policy.
>
>
> The way things are shaping up, we've had 17 years of rock solid
> stability, 1 release that incorporated changes that were designed to
> minimize impact, to the point that the majority of the objections
> against them are of the form where people would prefer that we broke
> _more_ code, to get a more sensible state. Going forward, it looks
> like the next 2 GHC releases will have basically nothing affecting the
> Prelude, and there will be another punctuation in the equilibrium
> around 8.4 as the next set of changes kicks in over 8.4 and 8.6 That
> gives 2 years worth of advance notice of pending changes, and a pretty
> strong guarantee from the committee that you should be able to
> maintain code with a 3 release window without running afoul of
> warnings or needing CPP.
>
> So, out of curiosity, what additional stability policy is it that you
> seek?

Thanks to you and Dan [1], I now have a greater understanding and
appreciation for where the committee has been coming from. My new
understanding is that the changes that were formalized in AMP, FTP, and
MRP were the basis for the committee's creation. It also 

Re: Breaking Changes and Long Term Support Haskell

[Geoffrey Mainland]

On 10/22/2015 11:02 AM, Matthias Hörmann wrote:
> I would say that the need to import Control.Applicative in virtually
> every module manually
> definitely caused some pain before AMP.

In this particular case, there is a trade off between breaking code on
the one hand and having to write some import statements on the other. I
find writing some extra imports less painful than breaking (other
people's and my) code, but the other position is defensible as well. I
sense that I am in the minority, at least on the libraries list.

> I would also argue that a
> non-negligible amount
> of effort goes into teaching the warts, the reasons for the warts and
> how to work around them.

Which wart(s) in particular? All of them? Does having return (and (>>))
in Monad make teaching more difficult?

I teach Haskell beginners, and I found that AMP made explaining monads
slightly more difficult because it served as a source of confusion for
my students.

On the other hand, the warts provide a teachable moment once students
understand all this stuff :)

>> Dealing with AMP? I'm working on a collaborative research project that is 
>> stuck on 7.8 because of AMP.
> I am curious what exactly about AMP causes your research project to be
> "stuck" on GHC 7.8
> considering we have had multiple people mention how little effort it
> took to update even large codebases.
> I think it would be useful information to have to plan future changes
> in a way that might avoid
> your issues.

I was hoping that mentioning this wouldn't distract from the three main
(numbered) questions I posed below. Alas.

If I were working alone, AMP wouldn't be a huge deal. I could fix the
code for 7.10 compatibility, but then unless everyone switches to 7.10,
changes to the codebase made by someone using 7.8, e.g., defining a new
Monad instance, could break things on 7.10 again. It's easier to stick
with 7.8. Any time spent dealing with compatibility issues is time not
spent writing actual code.

I outlined one possible path to avoid this kind of issue: spend more
time thinking about ways to maintain compatibility. We had proposals for
doing this with AMP.

Cheers,
Geoff

>
> On Thu, Oct 22, 2015 at 3:29 PM, Geoffrey Mainland  
> wrote:
>> On 10/22/2015 02:40 AM, Edward Kmett wrote:
>>> On Wed, Oct 21, 2015 at 8:42 PM, Gregory Collins
>>> > wrote:
>>>
>>>
>>> On Wed, Oct 21, 2015 at 3:18 PM, Geoffrey Mainland
>>> > wrote:
>>>
>>> My original email stated my underlying concern: we are losing
>>> valuable
>>> members of the community not because of the technical
>>> decisions that are
>>> being made, but because of the process by which they are being
>>> made.
>>>
>>> [If] you're doing research you're on the treadmill, almost by
>>> definition, and you're delighted that we're finally making some
>>> rapid progress on fixing up some of the longstanding warts.
>>>
>>> If you're a practitioner, you are interested in using Haskell for,
>>> y'know, writing programs. You're probably in one of two camps:
>>> you're in "green field" mode writing a lot of new code (early
>>> stage startups, prototype work, etc), or you're
>>> maintaining/extending programs you've already written that are out
>>> "in the field" for you doing useful work. Laura Wingerd calls this
>>> the "annealing temperature" of software, and I think this is a
>>> nice metaphor to describe it. How tolerant you are of ecosystem
>>> churn depends on what your temperature is: and I think it should
>>> be obvious to everyone that Haskell having "success" for
>>> programming work would mean that lots of useful and correct
>>> programs get written, so everyone who is in the former camp will
>>> cool over time to join the latter.
>>>
>>>
>>> I've made the point before and I don't really want to belabor it:
>>> our de facto collective posture towards breaking stuff, especially
>>> in the past few years, has been extremely permissive, and this
>>> alienates people who are maintaining working programs.
>>>
>>>
>>> Even among people who purported to be teaching Haskell or using
>>> Haskell today in industry the margin of preference for the concrete
>>> FTP proposal was ~79%. This was considerably higher than I expected in
>>> two senses. One: there were a lot more people who claimed to be in one
>>> of those two roles than I expected by far, and two: their appetite for
>>> change was higher than I expected. I initially expected to see a
>>> stronger "academic vs. industry" split in the poll, but the groups
>>> were only distinguishable by a few percentage point delta, so while I
>>> expected roughly the end percentage of the poll, based on the year
>>> prior I'd spent running around the planet to user group meetings and
>>> the like, I expected it 

Re: Breaking Changes and Long Term Support Haskell

[Edward Kmett]

On Thu, Oct 22, 2015 at 11:36 AM, Geoffrey Mainland 
wrote:

> On 10/22/2015 11:02 AM, Matthias Hörmann wrote:
> > I would say that the need to import Control.Applicative in virtually
> > every module manually
> > definitely caused some pain before AMP.
>
> In this particular case, there is a trade off between breaking code on
> the one hand and having to write some import statements on the other. I
> find writing some extra imports less painful than breaking (other
> people's and my) code, but the other position is defensible as well. I
> sense that I am in the minority, at least on the libraries list.
>
> > I would also argue that a
> > non-negligible amount
> > of effort goes into teaching the warts, the reasons for the warts and
> > how to work around them.
>
> Which wart(s) in particular? All of them? Does having return (and (>>))
> in Monad make teaching more difficult?
>

Having (>>) means that we have hundreds of monads out there where (>>) has
been optimized, but (*>) has not.

If I were working alone, AMP wouldn't be a huge deal. I could fix the
> code for 7.10 compatibility, but then unless everyone switches to 7.10,
> changes to the codebase made by someone using 7.8, e.g., defining a new
> Monad instance, could break things on 7.10 again. It's easier to stick
> with 7.8. Any time spent dealing with compatibility issues is time not
> spent writing actual code.
>

In the open source world many of us just fire off our code to travis-ci and
get it to build with a dozen different compiler versions. I maintain a lot
of code that supports things back to 7.0 and forward to HEAD this way.


> I outlined one possible path to avoid this kind of issue: spend more
> time thinking about ways to maintain compatibility. We had proposals for
> doing this with AMP.
>

And on the other hand we also had a concrete proposal that didn't require
language changes that was ridiculously popular. People had been talking
about Applicative as a superclass of Monad for a decade before we finally
acted upon the AMP. People had been talking about superclass defaulting for
a decade. When do you cut off discussion and ship the proposal that has
overwhelming support? If there is no process that enables this you can
stall the process indefinitely by raising objections of this form. Such a
situation is not without costs all its own.

-Edward


> Cheers,
> Geoff
>
> >
> > On Thu, Oct 22, 2015 at 3:29 PM, Geoffrey Mainland 
> wrote:
> >> On 10/22/2015 02:40 AM, Edward Kmett wrote:
> >>> On Wed, Oct 21, 2015 at 8:42 PM, Gregory Collins
> >>> > wrote:
> >>>
> >>>
> >>> On Wed, Oct 21, 2015 at 3:18 PM, Geoffrey Mainland
> >>> > wrote:
> >>>
> >>> My original email stated my underlying concern: we are losing
> >>> valuable
> >>> members of the community not because of the technical
> >>> decisions that are
> >>> being made, but because of the process by which they are being
> >>> made.
> >>>
> >>> [If] you're doing research you're on the treadmill, almost by
> >>> definition, and you're delighted that we're finally making some
> >>> rapid progress on fixing up some of the longstanding warts.
> >>>
> >>> If you're a practitioner, you are interested in using Haskell for,
> >>> y'know, writing programs. You're probably in one of two camps:
> >>> you're in "green field" mode writing a lot of new code (early
> >>> stage startups, prototype work, etc), or you're
> >>> maintaining/extending programs you've already written that are out
> >>> "in the field" for you doing useful work. Laura Wingerd calls this
> >>> the "annealing temperature" of software, and I think this is a
> >>> nice metaphor to describe it. How tolerant you are of ecosystem
> >>> churn depends on what your temperature is: and I think it should
> >>> be obvious to everyone that Haskell having "success" for
> >>> programming work would mean that lots of useful and correct
> >>> programs get written, so everyone who is in the former camp will
> >>> cool over time to join the latter.
> >>>
> >>>
> >>> I've made the point before and I don't really want to belabor it:
> >>> our de facto collective posture towards breaking stuff, especially
> >>> in the past few years, has been extremely permissive, and this
> >>> alienates people who are maintaining working programs.
> >>>
> >>>
> >>> Even among people who purported to be teaching Haskell or using
> >>> Haskell today in industry the margin of preference for the concrete
> >>> FTP proposal was ~79%. This was considerably higher than I expected in
> >>> two senses. One: there were a lot more people who claimed to be in one
> >>> of those two roles than I expected by far, and two: their appetite for
> >>> change was higher than I expected. I 

Re: Breaking Changes and Long Term Support Haskell

[Mario Blažević]

On 15-10-22 09:29 AM, Geoffrey Mainland wrote:

...

1) What is the master plan, and where is it documented, even if this
document is not up to the standard of a proposal? What is the final
target, and when might we expect it to be reached? What is in the
pipeline after MRP?

Relatedly, guidance on how to write code now so that it will be
compatible with future changes helps mitigate the stability issue.


	I have been fully in favour of all the proposals implemented so far, 
and I think that having an explicit master plan would be a great idea. 
It would address some of the process-related objections that have been 
raised, and it would provide a fixed long-term target that would be much 
easier to make the whole community aware of and contribute to.


	For that purpose, the master plan should be advertised directly on the 
front page of haskell.org. Once we have it settled and agreed, the 
purpose of the base-library commitee would essentially become to figure 
out the details like the timeline and code migration path. One thing 
they wouldn't need to worry about is whether anybody disagrees with 
their goals.




2) How can I write code that makes use of the Prelude so that it will
work with every new GHC release over the next 3 years? 5 years? For
example, how can I write a Monad instance now, knowing the changes that
are coming, so that the instance will work with every new GHC release
for the next 3 years? 5 years? If the answer is "you can't," then when
might I be able to do such a thing? As of 8.4? 8.6? I'm embarrassed to
say I don't know the answer!


	From the discussions so far it appears that the answer for 3 years (or 
at least the next 3 GHC releases) would be to write the code that works 
with the current GHC and base, but this policy has not been codified 
anywhere yet. Knowing the upcoming changes doesn't help with making your 
code any more robust, and I think that's a shame. We could have a 
two-pronged policy:


- code that works and compiles with the latest GHC with no *warnings* 
will continue to work and compile with no *errors* with the following 2 
releases, and
- code that also follows the forward-compatibility recommendations 
current for that version of GHC will continue to work and compile with 
no *errors* with the following 4 releases.


	The forward-compatibility recommendations would become a part of the 
online GHC documentation so nobody complains they didn't know about 
them. Personally, I'd prefer if the recommendations were built into the 
compiler itself as a new class of warnings, but then (a) some people 
would insist on turning them on together with -Werror and then complain 
when their builds break and (b) this would increase the pressure on GHC 
implementors.




Finally, if none of these changes broke Prelude backwards compatibility,
far fewer people would be complaining :) Of course, we can't always make
progress without breaking things, but a more deliberative process might
offer an opportunity to make progress while still preserving backwards
compatibility. Take AMP for example. There were at least two [3] [4]
proposals for preserving backwards compatibility. Investigating them
would have taken time and delayed AMP, yes, but why the rush?


Because they have been investigated for years with no effect.



3) Can we have a process that allows more deliberation over, and wider
publicity for, changes that break backwards compatibility? The goal of
such a process would not be to prevent change, but to allow more time to
find possible solution to the issue of backwards compatibility.


I doubt we can, but this question has already been answered by others.

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Re: Breaking Changes and Long Term Support Haskell

[Edward Kmett]

On Thu, Oct 22, 2015 at 12:20 PM, Mario Blažević 
wrote:

> On 15-10-22 09:29 AM, Geoffrey Mainland wrote:
>
>> ...
>>
>> 1) What is the master plan, and where is it documented, even if this
>> document is not up to the standard of a proposal? What is the final
>> target, and when might we expect it to be reached? What is in the
>> pipeline after MRP?
>>
>> Relatedly, guidance on how to write code now so that it will be
>> compatible with future changes helps mitigate the stability issue.
>>
>
> I have been fully in favour of all the proposals implemented so
> far, and I think that having an explicit master plan would be a great idea.
> It would address some of the process-related objections that have been
> raised, and it would provide a fixed long-term target that would be much
> easier to make the whole community aware of and contribute to.
>
> For that purpose, the master plan should be advertised directly on
> the front page of haskell.org. Once we have it settled and agreed, the
> purpose of the base-library commitee would essentially become to figure out
> the details like the timeline and code migration path. One thing they
> wouldn't need to worry about is whether anybody disagrees with their goals.
>
>
> 2) How can I write code that makes use of the Prelude so that it will
>> work with every new GHC release over the next 3 years? 5 years? For
>> example, how can I write a Monad instance now, knowing the changes that
>> are coming, so that the instance will work with every new GHC release
>> for the next 3 years? 5 years? If the answer is "you can't," then when
>> might I be able to do such a thing? As of 8.4? 8.6? I'm embarrassed to
>> say I don't know the answer!
>>
>
> From the discussions so far it appears that the answer for 3 years
> (or at least the next 3 GHC releases) would be to write the code that works
> with the current GHC and base, but this policy has not been codified
> anywhere yet. Knowing the upcoming changes doesn't help with making your
> code any more robust, and I think that's a shame. We could have a
> two-pronged policy:
>
> - code that works and compiles with the latest GHC with no *warnings* will
> continue to work and compile with no *errors* with the following 2
> releases, and
> - code that also follows the forward-compatibility recommendations current
> for that version of GHC will continue to work and compile with no *errors*
> with the following 4 releases.
>

We have adopted a "3 release policy" facing backwards, not forwards.
However, all proposals currently under discussion actually meet a stronger
condition, a 3 release policy that you can slide both forward and backwards
to pick the 3 releases you want to be compatible with without using CPP. It
also appears that all of the changes that we happen to have in the wings

https://ghc.haskell.org/trac/ghc/wiki/Status/BaseLibrary

comply with both of your goals here. However, I hesitate to say that we can
simultaneously meet this goal and the 3 release policy facing backwards
_and_ sufficient notification in all situations even ones we can't foresee
today. As a guideline? Sure. If we have two plans that can reach the same
end-goal and one complies and the other doesn't, I'd say we should favor
the plan that gives more notice and assurance. However, this also needs to
be tempered against the number of years folks suffer the pain of having in
an inconsistent intermediate state. (e.g. having generalized combinators in
Data.List today)

The forward-compatibility recommendations would become a part of
> the online GHC documentation so nobody complains they didn't know about
> them. Personally, I'd prefer if the recommendations were built into the
> compiler itself as a new class of warnings, but then (a) some people would
> insist on turning them on together with -Werror and then complain when
> their builds break and (b) this would increase the pressure on GHC
> implementors.


The current discussion is centering around adding a -Wcompat flag that
warns of changes that you maybe can't yet implement in a way that would be
backwards compatible with a 3 release backwards-facing window, but which
will eventually cause issues.

-Edward
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Re: Breaking Changes and Long Term Support Haskell

[Geoffrey Mainland]

> I outlined one possible path to avoid this kind of issue: spend more
> time thinking about ways to maintain compatibility. We had
> proposals for
> doing this with AMP.
>
>
> And on the other hand we also had a concrete proposal that didn't
> require language changes that was ridiculously popular. People had
> been talking about Applicative as a superclass of Monad for a decade
> before we finally acted upon the AMP. People had been talking about
> superclass defaulting for a decade. When do you cut off discussion and
> ship the proposal that has overwhelming support? If there is no
> process that enables this you can stall the process indefinitely by
> raising objections of this form. Such a situation is not without costs
> all its own.
>

I agree. It was certainly within the power of the committee to start a
clock and say something like "if we don't have a patch to GHC that
provides backwards compatibility for AMP within 1 year, we will push out
AMP as-is." Had I understand the implications of AMP at the time, or
even been aware that AMP was happening (I was actually actively working
on the GHC code base during that period), that certainly would have been
motivation for me to do something about it! *That* would be how one
could cut off discussion and ship a proposal.

I am not against changing the Prelude! But it sure would be nice if
-XHaskell98 gave me a Haskell 98 Prelude and -XHaskell2010 gave me a
Haskell 2010 Prelude, both of which could be used with external packages
that themselves used the more modern Prelude. Maybe that's impossible.
Setting a firm deadline to finding a solution to the compatibility issue
would have been a way to compromise. Ideally, changing the Prelude
wouldn't require breaking code written to use an older version of the
Prelude. Yes, attaining that goal would require more work.

Evolving the Prelude and maintaining compatibility are not necessarily
mutually exclusive options.

Cheers,
Geoff
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Re: Breaking Changes and Long Term Support Haskell

[Geoffrey Mainland]

On 10/21/2015 07:30 AM, Simon Peyton Jones wrote:
> Friends
>
> I think it's good for us to debate the question of how we should balance 
> innovation against change; and how we should make those decisions in future.  
> Geoff's message had some good ideas, especially this bit:
>
> |  Proposal 2: After a suitable period of discussion on the libraries list, 
> the
> |  Core Libraries Committee will summarize the arguments for and against a
> |  proposal and post it, along with a (justified) preliminary decision, to a
> |  low-traffic, announce-only email list. After another suitable period of
> |  discussion, they will issue a final decision. What is a suitable period of
> |  time? Perhaps that depends on the properties of the proposal, such as
> |  whether it breaks backwards compatibility.
>
> Identifying major changes to the libraries, and having a better publicised, 
> more RFC-like process for deliberating them, would be a good thing.  I 
> believe that the Core Libraries committee is thinking actively about this.
>
> |  Personally, I think AMP was the right thing to do, but I don't think FTP 
> was
> |  the right thing.
>
> These make good examples to motivate future changes to our process.  But in 
> the end FTP was subject to a pretty broad deliberative process, precisely 
> along the lines that Geoff suggests above.  We had two clearly-articulated 
> alternatives, a discrete call for opinions broadcast to every Haskell channel 
> we could find, a decent interval for people to respond, and (as it turned 
> out) a very clear preponderance of opinion in one direction.  In a big 
> community, even a broad consultation may yield a result that some think is 
> ill-advised.  That's part of the joyful burden of being a big community.
>
> Let's look forward, not back.  I think we can do better in future than we 
> have done in the past.  I don't think we can hope for unanimity, but I think 
> we can reasonably seek 
>
>  * transparency; 
>  * clarity about what decisions are on the table; 
>  * broad consultation about decisions that affect 
> a broad constituency; and 
>  * a decent opportunity to debate them without having 
> to be involved in massive email threads.  Let's try do to that.
>
> Simon
>
> PS: For what it's worth I'm less keen on Geoff's other proposal:
>
> |  Proposal 3: A decision regarding any proposal that significantly affects
> |  backwards compatibility is within the purview of the Haskell Prime
> |  Committee, not the Core Libraries Committee.
>
> *Precisely* the same issues will arise whether it's CLC or HPC.  And the HPC 
> is going to be jolly busy with language issues. Moving the question from one 
> group to another risks avoiding the issue rather than addressing it.

For the record, I am also not sure Proposal 3 is a good idea :)

However, I do think we could clarify what the respective
responsibilities of the core libraries committee and Haskell Prime
committees are.

One possible choice is that the core libraries committee is responsible
for changes to the core libraries that do not affect libraries in the
report. It is meant to be nimble, able to quickly deal with the large
volume of library changes that do not impact backwards compatibility.

In this scenario, the Haskell Prime committee, using a longer
deliberative process, would consider the more impactful library changes
and batch them up into new reports.

You are absolutely correct that moving the question to the Haskell Prime
committee risks pushing the issue around. The idea behind the separation
outlined above is to reduce the treadmill; the two bodies use different
processes, with different time frames, to arrive at decisions. Some
library decisions may deserve a longer deliberative process.

Cheers,
Geoff
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Re: Breaking Changes and Long Term Support Haskell

[Dan Doel]

For proposal 3, I don't see what difference it makes whether a
refreshed Haskell committee or a new libraries committee makes
decisions that affect backwards compatibility. A name doesn't ensure
good decision making. The only difference I can see is that the
Haskell committee might only publish final decisions every couple
years. But the Haskell report also isn't designed to describe
migration plans between feature revisions; unless the plan is to start
incorporating library deprecation and whatnot into the report (which
would be odd to me). But that would just be doing the same thing
slower, so it'd be little different than making library changes over 6
to 9 GHC versions instead of 3.

For proposal 2, I don't know how effective it will be in practice. I
believe it is already the job of a proposal submitter to summarize the
arguments made about it, according to the library proposal guidelines.
We could post those summaries to another list. But unless more people
promise they will be diligent about reading that list, I'm not sure
that one factor in these dust ups (surprise) will actually be any
different.

Also, if amount of discussion is at issue, I'm not sure I agree. For
AMP, I was waiting a decade, more or less. I thought we should do it,
other people thought we shouldn't because it would break things. I
don't know what more there was to discuss, except there was more stuff
to break the longer we waited.

As for FTP, some aspects only became known as the proposal was
implemented, and I don't know that they would have been realized
regardless of how long the proposal were discussed. And then we still
had a month or so of discussion after the implementation was
finalized, on the cusp of GHC 7.10 being released. So how much more
_was_ needed, that people are now discussing it again?

If it's just about documenting more things, there's certainly no harm in that.

For 1, I don't have a very strong opinion. If pressed, I would
probably express some similar sentiments to Henrik. I certainly don't
think Haskell would be nearly as good as it is if it were a simple
majority vote by all users (and I probably wouldn't use it if that's
how things were decided). Would a community vote for libraries
committee be better than appointment by people who previously held the
power (but have more to do than any human can accomplish)? I don't
know.

I should say, though, that things are not now run by simple majority
vote. What we conducted a year ago was a survey, where people
submitted their thoughts. I didn't get to read them, because they were
private, and it wasn't my decision to make. But it was not just +80
-20.

With regard to your last paragraph, unless I've missed something (and
I confess that I haven't read every comment in these threads), the
recent resignations didn't express disagreement with the decision
making process. They expressed disagreement with the (technical)
decisions (and their effects). I don't see how a different process
could have solved that unless it is expected that it would have made
different decisions.

-- Dan

On Wed, Oct 21, 2015 at 6:18 PM, Geoffrey Mainland  wrote:
> Hi Dan,
>
> Thank you for the historical perspective.
>
> I was careful not to criticize the committee. Instead, I made three
> concrete proposals with the hope that they would help orient a conversation.
>
> It sounds like you are not for proposal 3. How about the other two?
>
> My original email stated my underlying concern: we are losing valuable
> members of the community not because of the technical decisions that are
> being made, but because of the process by which they are being made.
> That concern is what drove my proposals. It is perfectly valid to think
> that that loss was the inevitable price of progress, but that is not my
> view.
>
> Cheers,
> Geoff
>
> On 10/21/15 5:22 PM, Dan Doel wrote:
>> Hello,
>>
>> I'm Dan Doel. I'm on the core libraries committee (though I'm speaking
>> only for myself). As I recall, one of the reasons I got tapped for it
>> was due to my having some historical knowledge about Haskell; not
>> because I was there, but because I've gone back and looked at some old
>> reports and whatnot (and sometimes think they're better than what we
>> have now).
>>
>> But, I was around (of course) when the core libraries committee
>> started up, so perhaps I can play the role of historian for this as
>> well.
>>
>> The reason the committee exists is because a couple years ago, people
>> brought up the ideas that were finally realized in the
>> Applicative-Monad proposal and the Foldable-Traversable proposal. A
>> lot of people weighed in saying they thought they were a good idea,
>> and significantly fewer people weighed in saying they thought that it
>> shouldn't happen for various reasons---roughly the same things that
>> people are still bringing up about these proposals.
>>
>> This wasn't the first time that happened, either. I think it was
>> widely agreed among most users 

Re: Breaking Changes and Long Term Support Haskell

[Dan Doel]

Hello,

I'm Dan Doel. I'm on the core libraries committee (though I'm speaking
only for myself). As I recall, one of the reasons I got tapped for it
was due to my having some historical knowledge about Haskell; not
because I was there, but because I've gone back and looked at some old
reports and whatnot (and sometimes think they're better than what we
have now).

But, I was around (of course) when the core libraries committee
started up, so perhaps I can play the role of historian for this as
well.

The reason the committee exists is because a couple years ago, people
brought up the ideas that were finally realized in the
Applicative-Monad proposal and the Foldable-Traversable proposal. A
lot of people weighed in saying they thought they were a good idea,
and significantly fewer people weighed in saying they thought that it
shouldn't happen for various reasons---roughly the same things that
people are still bringing up about these proposals.

This wasn't the first time that happened, either. I think it was
widely agreed among most users that Functor should be a superclass of
Monad since I started learning Haskell around 10 years ago. And once
Applicative was introduced, it was agreed that that should go in the
middle of the two. But it appeared that it would never happen, despite
a significant majority thinking it should, because no one wanted to do
anything without pretty much unanimous consent.

So, one question that got raised is: why should this majority of
people even use Haskell/GHC anymore? Why shouldn't they start using
some other language that will let them change 15-year-old mistakes, or
adapt to ideas that weren't even available at that time (but are still
fairly old and established, all things considered). And the answer was
that there should be some body empowered to decide to move forward
with these ideas, even if there is some dissent. And frankly, it
wasn't going to be the prime committee, because it hadn't shown any
activity in something like 3 years at the time, and even when it was
active, it didn't make anywhere near the sort of changes that were
being discussed.

And the kicker to me is, many things that people are complaining about
again (e.g. the FTP) were the very things that the committee was
established to execute. I don't think we had a formal vote on that
proposal, because we didn't need to. Our existence was in part to
execute that proposal (and AMP). And then a year ago, when it was
finally time to release the changes, there was another ruckus. And we
still didn't have a CLC vote on the matter. What we did was conduct a
community poll, and then SPJ reviewed the submissions. But I don't
mean to pass the buck to him, because I'm pretty sure he was worried
that we were crazy, and overstepping our bounds. Just, the results of
the survey were sufficient for him to not overrule us.

So my point is this: there seems to be some sentiment that the core
libraries committee is unsound, and making bad decisions. But the
complaints are mostly not even about actual decisions we made (aside
from maybe Lennart Augustsson's, where he is unhappy with details of
the FTP that you can blame on us, but were designed to break the least
code, instead of being the most elegant; if we had pleased him more,
we would have pleased others less). They are about the reasons for
founding the committee in the first place. You can blame us, if you
like, because I think it's certain that we would have approved them if
we had formally voted. We just didn't even need to do so.

Forgive me if I'm wrong, but suggestions that these decisions should
have been deferred to a Haskell Prime committee mean, to me, that the
hope is that they would have been rejected. That the Haskell Prime
committee should have just vetoed these proposals that something like
80% or more of practicing Haskell users (as far as we can tell) wanted
for years before they finally happened. That the Haskell Prime
committee should be responsible for enforcing the very status quo that
led to the CLC in the first place, where proposals with broad support
but minority dissent never pass for various core modules.

If this is the case, then one could simply repose the earlier
question: why should most of these people stick around to obey by the
Haskell Prime committee's pronouncements, instead of getting to work
on a language that incorporates their input?

And if it isn't, then I don't ultimately understand what the
complaints are. We try to accomplish the (large) changes in a manner
that allows transition via refactoring over multiple versions (and as
I mentioned earlier, some complaints are that we compromised _too
much_ for this). And in light of the more recent complaints, it's even
been decided that our time frames should be longer. Rolling up changes
into a report just seems like it makes transitions less smooth. Unless
the idea is to make GHC capable of switching out entire base library
sets; but someone has to implement that, and once you 

Re: Breaking Changes and Long Term Support Haskell

[Carter Schonwald]

Well said!

I do have a small worry that the longer roll out window will be harder to
manage given that every thing is done by (outstanding) volunteers.  But
maybe the answer there is that ghc should do major version releases more
frequently :), eg every 9 months instead of every 12! 

On Wednesday, October 21, 2015, Dan Doel  wrote:

> Hello,
>
> I'm Dan Doel. I'm on the core libraries committee (though I'm speaking
> only for myself). As I recall, one of the reasons I got tapped for it
> was due to my having some historical knowledge about Haskell; not
> because I was there, but because I've gone back and looked at some old
> reports and whatnot (and sometimes think they're better than what we
> have now).
>
> But, I was around (of course) when the core libraries committee
> started up, so perhaps I can play the role of historian for this as
> well.
>
> The reason the committee exists is because a couple years ago, people
> brought up the ideas that were finally realized in the
> Applicative-Monad proposal and the Foldable-Traversable proposal. A
> lot of people weighed in saying they thought they were a good idea,
> and significantly fewer people weighed in saying they thought that it
> shouldn't happen for various reasons---roughly the same things that
> people are still bringing up about these proposals.
>
> This wasn't the first time that happened, either. I think it was
> widely agreed among most users that Functor should be a superclass of
> Monad since I started learning Haskell around 10 years ago. And once
> Applicative was introduced, it was agreed that that should go in the
> middle of the two. But it appeared that it would never happen, despite
> a significant majority thinking it should, because no one wanted to do
> anything without pretty much unanimous consent.
>
> So, one question that got raised is: why should this majority of
> people even use Haskell/GHC anymore? Why shouldn't they start using
> some other language that will let them change 15-year-old mistakes, or
> adapt to ideas that weren't even available at that time (but are still
> fairly old and established, all things considered). And the answer was
> that there should be some body empowered to decide to move forward
> with these ideas, even if there is some dissent. And frankly, it
> wasn't going to be the prime committee, because it hadn't shown any
> activity in something like 3 years at the time, and even when it was
> active, it didn't make anywhere near the sort of changes that were
> being discussed.
>
> And the kicker to me is, many things that people are complaining about
> again (e.g. the FTP) were the very things that the committee was
> established to execute. I don't think we had a formal vote on that
> proposal, because we didn't need to. Our existence was in part to
> execute that proposal (and AMP). And then a year ago, when it was
> finally time to release the changes, there was another ruckus. And we
> still didn't have a CLC vote on the matter. What we did was conduct a
> community poll, and then SPJ reviewed the submissions. But I don't
> mean to pass the buck to him, because I'm pretty sure he was worried
> that we were crazy, and overstepping our bounds. Just, the results of
> the survey were sufficient for him to not overrule us.
>
> So my point is this: there seems to be some sentiment that the core
> libraries committee is unsound, and making bad decisions. But the
> complaints are mostly not even about actual decisions we made (aside
> from maybe Lennart Augustsson's, where he is unhappy with details of
> the FTP that you can blame on us, but were designed to break the least
> code, instead of being the most elegant; if we had pleased him more,
> we would have pleased others less). They are about the reasons for
> founding the committee in the first place. You can blame us, if you
> like, because I think it's certain that we would have approved them if
> we had formally voted. We just didn't even need to do so.
>
> Forgive me if I'm wrong, but suggestions that these decisions should
> have been deferred to a Haskell Prime committee mean, to me, that the
> hope is that they would have been rejected. That the Haskell Prime
> committee should have just vetoed these proposals that something like
> 80% or more of practicing Haskell users (as far as we can tell) wanted
> for years before they finally happened. That the Haskell Prime
> committee should be responsible for enforcing the very status quo that
> led to the CLC in the first place, where proposals with broad support
> but minority dissent never pass for various core modules.
>
> If this is the case, then one could simply repose the earlier
> question: why should most of these people stick around to obey by the
> Haskell Prime committee's pronouncements, instead of getting to work
> on a language that incorporates their input?
>
> And if it isn't, then I don't ultimately understand what the
> complaints are. We try to 

RE: Breaking Changes and Long Term Support Haskell

[Simon Peyton Jones]

While we are here, let me say

  A BIG THANK YOU TO THE CORE LIBRARIES COMMITTEE

Library design has a lot of detail, and a lot of competing priorities.  I am 
personally very grateful to the CLC for the work they put into this. Like many 
crucial tasks it's one that often seems to attract more complaints than thanks, 
but they are doing us all a huge service, and at significant cost in terms of 
their most precious and inelastic commodity: their personal time.

Remember, as Dan says, before the CLC we no process whatsoever for library 
evolution... various people made various patches, and there was no way of 
getting anything substantial done.  So we are far far further on than before.

Still not perfect, as my last post said. But still: THANK YOU.

Simon

| -Original Message-
| From: Dan Doel [mailto:dan.d...@gmail.com]
| Sent: 21 October 2015 22:23
| To: Geoffrey Mainland
| Cc: Simon Peyton Jones; Augustsson, Lennart; Henrik Nilsson; haskell-
| pr...@haskell.org List; Haskell Libraries
| Subject: Re: Breaking Changes and Long Term Support Haskell
| 
| Hello,
| 
| I'm Dan Doel. I'm on the core libraries committee (though I'm speaking
| only for myself). As I recall, one of the reasons I got tapped for it
| was due to my having some historical knowledge about Haskell; not
| because I was there, but because I've gone back and looked at some old
| reports and whatnot (and sometimes think they're better than what we
| have now).
| 
| But, I was around (of course) when the core libraries committee
| started up, so perhaps I can play the role of historian for this as
| well.
| 
| The reason the committee exists is because a couple years ago, people
| brought up the ideas that were finally realized in the
| Applicative-Monad proposal and the Foldable-Traversable proposal. A
| lot of people weighed in saying they thought they were a good idea,
| and significantly fewer people weighed in saying they thought that it
| shouldn't happen for various reasons---roughly the same things that
| people are still bringing up about these proposals.
| 
| This wasn't the first time that happened, either. I think it was
| widely agreed among most users that Functor should be a superclass of
| Monad since I started learning Haskell around 10 years ago. And once
| Applicative was introduced, it was agreed that that should go in the
| middle of the two. But it appeared that it would never happen, despite
| a significant majority thinking it should, because no one wanted to do
| anything without pretty much unanimous consent.
| 
| So, one question that got raised is: why should this majority of
| people even use Haskell/GHC anymore? Why shouldn't they start using
| some other language that will let them change 15-year-old mistakes, or
| adapt to ideas that weren't even available at that time (but are still
| fairly old and established, all things considered). And the answer was
| that there should be some body empowered to decide to move forward
| with these ideas, even if there is some dissent. And frankly, it
| wasn't going to be the prime committee, because it hadn't shown any
| activity in something like 3 years at the time, and even when it was
| active, it didn't make anywhere near the sort of changes that were
| being discussed.
| 
| And the kicker to me is, many things that people are complaining about
| again (e.g. the FTP) were the very things that the committee was
| established to execute. I don't think we had a formal vote on that
| proposal, because we didn't need to. Our existence was in part to
| execute that proposal (and AMP). And then a year ago, when it was
| finally time to release the changes, there was another ruckus. And we
| still didn't have a CLC vote on the matter. What we did was conduct a
| community poll, and then SPJ reviewed the submissions. But I don't
| mean to pass the buck to him, because I'm pretty sure he was worried
| that we were crazy, and overstepping our bounds. Just, the results of
| the survey were sufficient for him to not overrule us.
| 
| So my point is this: there seems to be some sentiment that the core
| libraries committee is unsound, and making bad decisions. But the
| complaints are mostly not even about actual decisions we made (aside
| from maybe Lennart Augustsson's, where he is unhappy with details of
| the FTP that you can blame on us, but were designed to break the least
| code, instead of being the most elegant; if we had pleased him more,
| we would have pleased others less). They are about the reasons for
| founding the committee in the first place. You can blame us, if you
| like, because I think it's certain that we would have approved them if
| we had formally voted. We just didn't even need to do so.
| 
| Forgive me if I'm wrong, but suggestions that these decisions should
| have been deferred to a Haskell Prime committee mean, to me, that the
| hope is that they would have been rejected. That the Haskell Prime
| committee should have just vetoed

Re: Breaking Changes and Long Term Support Haskell

[Geoffrey Mainland]

Hi Dan,

Thank you for the historical perspective.

I was careful not to criticize the committee. Instead, I made three
concrete proposals with the hope that they would help orient a conversation.

It sounds like you are not for proposal 3. How about the other two?

My original email stated my underlying concern: we are losing valuable
members of the community not because of the technical decisions that are
being made, but because of the process by which they are being made.
That concern is what drove my proposals. It is perfectly valid to think
that that loss was the inevitable price of progress, but that is not my
view.

Cheers,
Geoff

On 10/21/15 5:22 PM, Dan Doel wrote:
> Hello,
>
> I'm Dan Doel. I'm on the core libraries committee (though I'm speaking
> only for myself). As I recall, one of the reasons I got tapped for it
> was due to my having some historical knowledge about Haskell; not
> because I was there, but because I've gone back and looked at some old
> reports and whatnot (and sometimes think they're better than what we
> have now).
>
> But, I was around (of course) when the core libraries committee
> started up, so perhaps I can play the role of historian for this as
> well.
>
> The reason the committee exists is because a couple years ago, people
> brought up the ideas that were finally realized in the
> Applicative-Monad proposal and the Foldable-Traversable proposal. A
> lot of people weighed in saying they thought they were a good idea,
> and significantly fewer people weighed in saying they thought that it
> shouldn't happen for various reasons---roughly the same things that
> people are still bringing up about these proposals.
>
> This wasn't the first time that happened, either. I think it was
> widely agreed among most users that Functor should be a superclass of
> Monad since I started learning Haskell around 10 years ago. And once
> Applicative was introduced, it was agreed that that should go in the
> middle of the two. But it appeared that it would never happen, despite
> a significant majority thinking it should, because no one wanted to do
> anything without pretty much unanimous consent.
>
> So, one question that got raised is: why should this majority of
> people even use Haskell/GHC anymore? Why shouldn't they start using
> some other language that will let them change 15-year-old mistakes, or
> adapt to ideas that weren't even available at that time (but are still
> fairly old and established, all things considered). And the answer was
> that there should be some body empowered to decide to move forward
> with these ideas, even if there is some dissent. And frankly, it
> wasn't going to be the prime committee, because it hadn't shown any
> activity in something like 3 years at the time, and even when it was
> active, it didn't make anywhere near the sort of changes that were
> being discussed.
>
> And the kicker to me is, many things that people are complaining about
> again (e.g. the FTP) were the very things that the committee was
> established to execute. I don't think we had a formal vote on that
> proposal, because we didn't need to. Our existence was in part to
> execute that proposal (and AMP). And then a year ago, when it was
> finally time to release the changes, there was another ruckus. And we
> still didn't have a CLC vote on the matter. What we did was conduct a
> community poll, and then SPJ reviewed the submissions. But I don't
> mean to pass the buck to him, because I'm pretty sure he was worried
> that we were crazy, and overstepping our bounds. Just, the results of
> the survey were sufficient for him to not overrule us.
>
> So my point is this: there seems to be some sentiment that the core
> libraries committee is unsound, and making bad decisions. But the
> complaints are mostly not even about actual decisions we made (aside
> from maybe Lennart Augustsson's, where he is unhappy with details of
> the FTP that you can blame on us, but were designed to break the least
> code, instead of being the most elegant; if we had pleased him more,
> we would have pleased others less). They are about the reasons for
> founding the committee in the first place. You can blame us, if you
> like, because I think it's certain that we would have approved them if
> we had formally voted. We just didn't even need to do so.
>
> Forgive me if I'm wrong, but suggestions that these decisions should
> have been deferred to a Haskell Prime committee mean, to me, that the
> hope is that they would have been rejected. That the Haskell Prime
> committee should have just vetoed these proposals that something like
> 80% or more of practicing Haskell users (as far as we can tell) wanted
> for years before they finally happened. That the Haskell Prime
> committee should be responsible for enforcing the very status quo that
> led to the CLC in the first place, where proposals with broad support
> but minority dissent never pass for various core modules.
>
> If this is the case, then 

RE: Breaking Changes and Long Term Support Haskell

[Simon Peyton Jones]

| For the record, I am also not sure Proposal 3 is a good idea :)
| 
| However, I do think we could clarify what the respective
| responsibilities of the core libraries committee and Haskell Prime
| committees are.

My instinct is this:
  Haskell Prime: language
  Core Libraries Committee: libraries

That seems simple.  If we try to move the largest and most challenging library 
design tasks from CLC to HP, I fear that we will overload the latter and 
devalue the former.

| You are absolutely correct that moving the question to the Haskell Prime
| committee risks pushing the issue around. The idea behind the separation
| outlined above is to reduce the treadmill; the two bodies use different
| processes, with different time frames, to arrive at decisions. Some
| library decisions may deserve a longer deliberative process.

I do agree that some library changes are far-reaching, and need a more 
deliberative process.  I think the CLC is in the process of developing such a 
process.  Moreover, I trust them to be able to tell the difference between 
low-impact and high-impact changes.

That said, as HP moves towards a new language Report, it would be good if CLC 
similarly moved towards a new libraries Report, so that there was a single 
unified document, just as we have had to date.

Simon


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Re: Breaking Changes and Long Term Support Haskell

[Henrik Nilsson]

Hi Dan,

Thanks for the history lesson. You do make many valid points.
And I also want to say thank you for the hard work that CLC
has put in.

Let me nevertheless react to a handful of things:

> And the answer was that there should be some body empowered to decide
> to move forward with these ideas, even if there is some dissent. And
> frankly, it wasn't going to be the prime committee, because it hadn't
> shown any activity in something like 3 years at the time, and even
> when it was active, it didn't make anywhere near the sort of changes
> that were being discussed.

I have seen criticism of the Haskell committee along similar lines
before, but I think it is overly simplistic, and arguably unfair,
for two reasons. First, squarely measuring accomplishment in terms
of number or scope of changes, which seems to be the gist (apologies
if I misunderstand), is, frankly, naive. In many ways, what didn't
change, for example, can be at least as important as what did for
establishing a language as a viable and attractive proposition for
large scale work. And the value of that for a language community as a
whole is hard to overstate. Now, I have no real data to back up that the
committee achieved that. But it is clear that Haskell has grown
a lot over the past 5 to 10 years, i.e. well before AMP, FTP, etc.
So maybe the last instance of the Haskell committee actually achieved
a great deal more than some seem willing to give it credit for.

Secondly, let us not forget that at least one highly controversial
and very breaking change was adopted for Haskell 2010: dropping
n + k patterns. The reason that went through was that there were very
compelling technical reasons and ultimately a clear case for
the advantages outweighing the disadvantages by a wide margin. So it is
not as if a committee cannot make controversial decisions. That does
presuppose that the majority of its members fundamentally have the 
interest of the community at large at the fore, and are willing to take

good arguments aboard, rather than being prone to take stances mainly
for "political" reasons. Fortunately, I strongly believe the Haskell
community by and large is rational in this sense.

> Forgive me if I'm wrong, but suggestions that these decisions should
> have been deferred to a Haskell Prime committee mean, to me, that the
> hope is that they would have been rejected.

OK, you are forgiven! I can of course only speak for myself, but I have
followed this discussion very carefully, and discussed with many people
in person. And as far as I can tell, there is absolutely nothing to
suggest that the reason that those who are unhappy with the process by
which AMP, FTP etc. happened (or by some of the details of those
proposals)  raise the possibility that the Haskell committee in one way
or another should have been (or in the future be) involved at least as
a vetting instance when it comes to the most far-reaching library
changes, is a secret hope of "death by committee".

Anyway, whether there are one or two committees ultimately does not
really matter, as long as both are widely seen to have a wide mandate
for whatever they are entrusted with, and as long as the process for
far-reaching changes is sufficiently robust and long.

> That the Haskell Prime
> committee should have just vetoed these proposals that something like
> 80% or more of practicing Haskell users (as far as we can tell) wanted
> for years before they finally happened.

Now, I have no desire to diminish the significance of the outcome of
that poll. Nor have I any desire to be branded as an "anti-democrat".
But if I am, so be it: I am bracing myself.

However, I have to point out that there is a lot more to
well-functioning democracies than simple majority votes. Look at any
developed democracy and there are lots of checks and balances in place
to safe-guard the interests of an as broad part of the population as
possible. In a federated state, just to give one example, there is
often a bicameral parliament where the states (broadly) have equal say
in one of the chambers irrespective of their size.

And yes, the workings of democracies are slow, sometimes painfully
so, but fundamentally that is for good reason.

To return to the case of a programming language community,
it is pretty much by definition going to be the case that a small
part of that community will be hit disproportionately hard by
changes to the language and/or its core libraries.

Their interests need to be adequately safeguarded too, or they will
surely jump ship in search of high and dry ground rather than run the
risk of drowning in the next wave of changes.

This, to the best of my understanding, is where I and others who
are suggesting that far-reaching changes should go past a
committee with a clear mandate and a sufficiently robust and long
process are coming from.

And I believe this is also what underlies Lennart's sentiment:

> I think voting to decide these kind of issues a terrible idea; we
> 

Re: Breaking Changes and Long Term Support Haskell

[Tony Morris]

Thanks Dan and others on CLC for your hard work and endurance.


On 22/10/15 07:48, Simon Peyton Jones wrote:
> While we are here, let me say
> 
>   A BIG THANK YOU TO THE CORE LIBRARIES COMMITTEE
> 
> Library design has a lot of detail, and a lot of competing priorities.  I am 
> personally very grateful to the CLC for the work they put into this. Like 
> many crucial tasks it's one that often seems to attract more complaints than 
> thanks, but they are doing us all a huge service, and at significant cost in 
> terms of their most precious and inelastic commodity: their personal time.
> 
> Remember, as Dan says, before the CLC we no process whatsoever for library 
> evolution... various people made various patches, and there was no way of 
> getting anything substantial done.  So we are far far further on than before.
> 
> Still not perfect, as my last post said. But still: THANK YOU.
> 
> Simon
> 
> | -Original Message-
> | From: Dan Doel [mailto:dan.d...@gmail.com]
> | Sent: 21 October 2015 22:23
> | To: Geoffrey Mainland
> | Cc: Simon Peyton Jones; Augustsson, Lennart; Henrik Nilsson; haskell-
> | pr...@haskell.org List; Haskell Libraries
> | Subject: Re: Breaking Changes and Long Term Support Haskell
> | 
> | Hello,
> | 
> | I'm Dan Doel. I'm on the core libraries committee (though I'm speaking
> | only for myself). As I recall, one of the reasons I got tapped for it
> | was due to my having some historical knowledge about Haskell; not
> | because I was there, but because I've gone back and looked at some old
> | reports and whatnot (and sometimes think they're better than what we
> | have now).
> | 
> | But, I was around (of course) when the core libraries committee
> | started up, so perhaps I can play the role of historian for this as
> | well.
> | 
> | The reason the committee exists is because a couple years ago, people
> | brought up the ideas that were finally realized in the
> | Applicative-Monad proposal and the Foldable-Traversable proposal. A
> | lot of people weighed in saying they thought they were a good idea,
> | and significantly fewer people weighed in saying they thought that it
> | shouldn't happen for various reasons---roughly the same things that
> | people are still bringing up about these proposals.
> | 
> | This wasn't the first time that happened, either. I think it was
> | widely agreed among most users that Functor should be a superclass of
> | Monad since I started learning Haskell around 10 years ago. And once
> | Applicative was introduced, it was agreed that that should go in the
> | middle of the two. But it appeared that it would never happen, despite
> | a significant majority thinking it should, because no one wanted to do
> | anything without pretty much unanimous consent.
> | 
> | So, one question that got raised is: why should this majority of
> | people even use Haskell/GHC anymore? Why shouldn't they start using
> | some other language that will let them change 15-year-old mistakes, or
> | adapt to ideas that weren't even available at that time (but are still
> | fairly old and established, all things considered). And the answer was
> | that there should be some body empowered to decide to move forward
> | with these ideas, even if there is some dissent. And frankly, it
> | wasn't going to be the prime committee, because it hadn't shown any
> | activity in something like 3 years at the time, and even when it was
> | active, it didn't make anywhere near the sort of changes that were
> | being discussed.
> | 
> | And the kicker to me is, many things that people are complaining about
> | again (e.g. the FTP) were the very things that the committee was
> | established to execute. I don't think we had a formal vote on that
> | proposal, because we didn't need to. Our existence was in part to
> | execute that proposal (and AMP). And then a year ago, when it was
> | finally time to release the changes, there was another ruckus. And we
> | still didn't have a CLC vote on the matter. What we did was conduct a
> | community poll, and then SPJ reviewed the submissions. But I don't
> | mean to pass the buck to him, because I'm pretty sure he was worried
> | that we were crazy, and overstepping our bounds. Just, the results of
> | the survey were sufficient for him to not overrule us.
> | 
> | So my point is this: there seems to be some sentiment that the core
> | libraries committee is unsound, and making bad decisions. But the
> | complaints are mostly not even about actual decisions we made (aside
> | from maybe Lennart Augustsson's, where he is unhappy with details of
> | the FTP that you can blame on us, but were designed to break the least
> | code, instead of being the most elegant; if we had pleased him mor

Re: Breaking Changes and Long Term Support Haskell

[Henrik Nilsson]

Hi all,

Jeremy wrote:

> There seems to be a fair amount of friction between those who want to
> introduce new features or fix significant historical warts in the base
> libraries - even if this requires breaking changes - and those who
> insist on no significant breaking changes in new releases, regardless
> of the reason or how much warning was given.

With respect, and without commenting on the merits of the proposal that
is then outlined (Long-Term Support Haskell), I don't think this is
an accurate description of the two main positions in the debate at all.

Most of those who have argued against MRP, for example, have made it
very clear that they are not at all against any breaking change. But
they oppose breaking changes to Haskell itself, including central
libraries, as defined by the Haskell report, unless the benefits are
very compelling indeed.

Speaking for myself, I have had to clarify this position a number
of times now, as there has been a tendency by the some proponents of
the proposed changes to suggest that those who disagree are against
all changes, the long term implication being that Haskell would
"stagnate and die".

And in the light of the above, I felt compelled to clarify this
position again.

It's not about no more changes ever. It is about ensuring that
changes are truly worthwhile and have wide support.

Best,

/Henrik

--
Henrik Nilsson
School of Computer Science
The University of Nottingham
n...@cs.nott.ac.uk




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RE: Breaking Changes and Long Term Support Haskell

[Augustsson, Lennart]

I'd like to vehemently agree with Henrik here. :)

Personally, I think AMP was the right thing to do, but I don't think FTP was 
the right thing.
And I don't think changes that break code are necessarily bad either, just some 
of them.

(To clarify, I'm against the Foldable class, but not Traversable.  It would 
have been quite feasible to have the latter, but not the former.)

  -- Lennart


-Original Message-
From: Haskell-prime [mailto:haskell-prime-boun...@haskell.org] On Behalf Of 
Henrik Nilsson
Sent: 21 October 2015 11:17
To: haskell-prime@haskell.org List; Haskell Libraries
Subject: Re: Breaking Changes and Long Term Support Haskell

Hi all,

Jeremy wrote:

 > There seems to be a fair amount of friction between those who want to  > 
 > introduce new features or fix significant historical warts in the base  > 
 > libraries - even if this requires breaking changes - and those who  > insist 
 > on no significant breaking changes in new releases, regardless  > of the 
 > reason or how much warning was given.

With respect, and without commenting on the merits of the proposal that is then 
outlined (Long-Term Support Haskell), I don't think this is an accurate 
description of the two main positions in the debate at all.

Most of those who have argued against MRP, for example, have made it very clear 
that they are not at all against any breaking change. But they oppose breaking 
changes to Haskell itself, including central libraries, as defined by the 
Haskell report, unless the benefits are very compelling indeed.

Speaking for myself, I have had to clarify this position a number of times now, 
as there has been a tendency by the some proponents of the proposed changes to 
suggest that those who disagree are against all changes, the long term 
implication being that Haskell would "stagnate and die".

And in the light of the above, I felt compelled to clarify this position again.

It's not about no more changes ever. It is about ensuring that changes are 
truly worthwhile and have wide support.

Best,

/Henrik

--
Henrik Nilsson
School of Computer Science
The University of Nottingham
n...@cs.nott.ac.uk




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RE: Breaking Changes and Long Term Support Haskell

[Simon Peyton Jones]

Friends

I think it's good for us to debate the question of how we should balance 
innovation against change; and how we should make those decisions in future.  
Geoff's message had some good ideas, especially this bit:

|  Proposal 2: After a suitable period of discussion on the libraries list, the
|  Core Libraries Committee will summarize the arguments for and against a
|  proposal and post it, along with a (justified) preliminary decision, to a
|  low-traffic, announce-only email list. After another suitable period of
|  discussion, they will issue a final decision. What is a suitable period of
|  time? Perhaps that depends on the properties of the proposal, such as
|  whether it breaks backwards compatibility.

Identifying major changes to the libraries, and having a better publicised, 
more RFC-like process for deliberating them, would be a good thing.  I believe 
that the Core Libraries committee is thinking actively about this.

|  Personally, I think AMP was the right thing to do, but I don't think FTP was
|  the right thing.

These make good examples to motivate future changes to our process.  But in the 
end FTP was subject to a pretty broad deliberative process, precisely along the 
lines that Geoff suggests above.  We had two clearly-articulated alternatives, 
a discrete call for opinions broadcast to every Haskell channel we could find, 
a decent interval for people to respond, and (as it turned out) a very clear 
preponderance of opinion in one direction.  In a big community, even a broad 
consultation may yield a result that some think is ill-advised.  That's part of 
the joyful burden of being a big community.

Let's look forward, not back.  I think we can do better in future than we have 
done in the past.  I don't think we can hope for unanimity, but I think we can 
reasonably seek 

 * transparency; 
 * clarity about what decisions are on the table; 
 * broad consultation about decisions that affect 
a broad constituency; and 
 * a decent opportunity to debate them without having 
to be involved in massive email threads.  Let's try do to that.

Simon

PS: For what it's worth I'm less keen on Geoff's other proposal:

|  Proposal 3: A decision regarding any proposal that significantly affects
|  backwards compatibility is within the purview of the Haskell Prime
|  Committee, not the Core Libraries Committee.

*Precisely* the same issues will arise whether it's CLC or HPC.  And the HPC is 
going to be jolly busy with language issues. Moving the question from one group 
to another risks avoiding the issue rather than addressing it.
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