[Haskell-cafe] Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`

John Lato jwlato at gmail.com
Mon Oct 5 18:33:42 UTC 2015

I think code-based weighting should not be considered at all. There's a
non-trivial amount of proprietary code that wouldn't be counted, and likely
can't be accounted for accurately. I have some unknown amount of code at my
previous employer (which does include Monad instances) that now has to be
maintained by others. I may have said +1 (and I'm reconsidering), but the
current maintainers probably don't want the extra make-work this involves.

There's an argument that this proposal involves very little up-front
breakage. This is true but disingenuous, because the breakage will still
happen in the future unless changes are made and committed. The entire
maintenance load should be considered, not just the immediate load.

Bryan, nothing I've seen since I started using Haskell makes me think that
the libraries committee or ghc devs value back compatibility much at all.
My favorite example is RecursiveDo, which was deprecated in favor of DoRec,
only for that to be reversed in the next ghc release. Of course that was
more irritating than breaking, but it's indicative of the general value
placed on maintenance programming.

On 12:28, Mon, Oct 5, 2015 Dimitri DeFigueiredo <defigueiredo at ucdavis.edu>

> +1
> I think this idea is good and should not be taken lightly. I'm a newcomer
> to the community and currently hold a grand total of *zero* open source
> contributions. Obviously, I would like to change this soon, but I think it
> is very *unfair* and makes absolutely no sense to have the standard one
> person one vote rule for decisions involving the libraries.
> Let the code produced vote. Maybe weight them by downloads?
> Dimitri
> On 10/5/15 9:12 AM, Johan Tibell wrote:
> Perhaps we should weigh the +1 and -1s in this thread with the number of
> lines of Haskell written by the voter? ;)
> On Mon, Oct 5, 2015 at 5:09 PM, Gershom B <gershomb at gmail.com> wrote:
>> On October 5, 2015 at 10:59:35 AM, Bryan O'Sullivan (bos at serpentine.com)
>> wrote:
>> > I would like to suggest that the bar for breaking all existing
>> libraries, books, papers,
>> > and lecture notes should be very high; and that the benefit associated
>> with such a breaking
>> > change should be correspondingly huge.
>> >
>> My understanding of the argument here, which seems to make sense to me,
>> is that the AMP already introduced a significant breaking change with
>> regards to monads. Books and lecture notes have already not caught up to
>> this, by and large. Hence, by introducing a further change, which
>> _completes_ the general AMP project, then by the time books and lecture
>> notes are all updated, they will be able to tell a much nicer story than
>> the current one?
>> As for libraries, it has been pointed out, I believe, that without CPP
>> one can write instances compatible with AMP, and also with AMP + MRP. One
>> can also write code, sans CPP, compatible with pre- and post- AMP.
>> So the reason for choosing to not do MRP simultaneous with AMP was
>> precisely to allow a gradual migration path where, sans CPP, people could
>> write code compatible with the last three versions of GHC, as the general
>> criteria has been.
>> So without arguing the necessity or not, I just want to weigh in with a
>> technical opinion that if this goes through, my _estimation_ is that there
>> will be a smooth and relatively painless migration period, the sky will not
>> fall, good teaching material will remain good, those libraries that bitrot
>> will tend to do so for a variety of reasons more significant than this, etc.
>> It is totally reasonable to have a discussion on whether this change is
>> worth it at all. But let’s not overestimate the cost of it just to further
>> tip the scales :-)
>> —gershom
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