Proposal: Make minimumBy and maximumBy go through foldl1

[Carter Schonwald]

Agreed.  There's better ways of integrating linear types into core.
On Wed, Jan 25, 2017 at 10:56 PM David Feuer <david.feuer at gmail.com> wrote:

> I do not like the idea of linearity being a *syntactic* construct
> rather than part of the type system. It seems likely to end up
> limiting us in confusing ways. Also, I like types. But that's really
> not relevant to this discussion.
>
> On Wed, Jan 25, 2017 at 10:31 PM, Joe Hillenbrand <joehillen at gmail.com>
> wrote:
> > Would you care to elaborate?
> >
> > On Wed, Jan 25, 2017 at 6:34 PM, David Feuer <david.feuer at gmail.com>
> wrote:
> >> I doubt it very much, and some of us have serious doubts about the
> >> extension as it stands.
> >>
> >> On Wed, Jan 25, 2017 at 8:58 PM, Joe Hillenbrand <joehillen at gmail.com>
> wrote:
> >>> Would the (hopeful) imminent linear types extension help here?
> >>>
> >>> On Wed, Jan 25, 2017 at 4:24 PM, Edward Kmett <ekmett at gmail.com>
> wrote:
> >>>> The current intent based on the ghc ticket traffic is to switch the
> >>>> implementation to foldl1 for the next release as a stopgap, but leave
> the
> >>>> door open to do something smarter in the future.
> >>>>
> >>>> The current foldr1 implementation is simply never a win, and a
> monoidal
> >>>> version devolves to a right fold for lists with the same bad behavior.
> >>>>
> >>>> If we later on figure out a way to efficiently exploit a strict
> monoidal
> >>>> accumulator for monoids that don't benefit from short-circuiting then
> a
> >>>> number of current Foldable combinators could benefit including this
> one, so
> >>>> we definitely want to leave the door open to doing things better in
> the
> >>>> future, but for now the left fold is an easy improvement over the
> status
> >>>> quo.
> >>>>
> >>>> -Edward
> >>>>
> >>>> On Wed, Jan 25, 2017 at 6:50 PM, David Laing <dave.laing.80 at gmail.com
> >
> >>>> wrote:
> >>>>>
> >>>>> Hi all,
> >>>>>
> >>>>> I'm proposing that the implementations of minimumBy and maximumBy be
> >>>>> changed from using foldl1 to foldr1.
> >>>>>
> >>>>> I found this in a GHC trac ticket[0] labelled 'Newcomer' that has
> more
> >>>>> details / discussion on that.
> >>>>>
> >>>>> The points that stand out to me are:
> >>>>> - the Haskell report says that those methods should be implemented in
> >>>>> terms of foldl1 (although as instance methods of Foldable there
> might be
> >>>>> some wiggle room there)
> >>>>> - it helps solves a space leak (which at first glance feels like it
> might
> >>>>> be a more common problem than the options that foldl1 removes)
> >>>>> - from the discussion on the ticket, it seemed to be an agreeable
> middle
> >>>>> ground
> >>>>>
> >>>>> As a side note: there have been a few proposals in the past to switch
> >>>>> these functions to use foldl', which seemed to have stalled.  I
> don't know
> >>>>> what the etiquette is around bringing up minor variations on old
> proposals
> >>>>> again, so I apologise if I've breached some kind of protocol here.
> >>>>>
> >>>>> Although I guess I've already breached one protocol by pushing a
> patch to
> >>>>> Phabricator for review without getting sign-off from the Core
> Libraries
> >>>>> Committee, so at least I'm being even handed with my clumsiness :)
> >>>>>
> >>>>> Cheers,
> >>>>>
> >>>>> Dave
> >>>>>
> >>>>> [0] https://ghc.haskell.org/trac/ghc/ticket/10830
> >>>>>
> >>>>>
> >>>>> _______________________________________________
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> >>>>>
> >>>>
> >>>>
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