Records in Haskell

[Simon Peyton-Jones]

Are Records stalled out again? I am perfectly willing to leave the fate of records up to a willing and capable implementer. That seems much better than waiting another 5 years for perfection :)

Yes, they are stalled again.  The "simple solution" turned out to be not simple.  I wrote it up at length in
            http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields
There are various unsatisfactory aspects of the proposal, particularly concerning record update.  I am not sure how to resolve them.

There was essentially no reaction.  As it's quite a lot of work to implement, and no one seemed to care very much, I put it back on the back burner.   So that's where it stands.

Meanwhile, AntC has put forth another proposal that I have not had time to look at in detail.
http://www.haskell.org/pipermail/glasgow-haskell-users/2011-December/021298.html

What this needs is someone (not me) to lead the discussion and try to make sure it makes progress.  For example, does AntC's proposal work? Is it better than the one I articulated?  Are any other variants worth considering? Is the gain from overloading record fields worth the pain or design and implementation?    Volunteers, stand forth!

Simon


From: Greg Weber [mailto:greg at gregweber.info]
Sent: 09 December 2011 19:38
To: Simon Peyton-Jones
Cc: Wolfgang Jeltsch; glasgow-haskell-users at haskell.org
Subject: Re: Records in Haskell

Are Records stalled out again? I am perfectly willing to leave the fate of records up to a willing and capable implementer. That seems much better than waiting another 5 years for perfection :)

As an intermediate step, is it possible to put a warning in 7.4 when the dot operator is used without a space so that it can be reserved for usage with a records solution? Or will the new records solution be turned on by an extension anyways?

On Mon, Nov 7, 2011 at 10:21 AM, Simon Peyton-Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>> wrote:
| would inclusion of such a record system into GHC mean that plans for
| first-class labels (<http://tinyurl.com/7fppj32>) are abandoned? That
| would be a pity, since first-class labels are very useful to implement
| record systems that go beyond what the abovementioned record system
| provides. See, for example, my work on records:
|      <http://www.informatik.tu-cottbus.de/~jeltsch/research/ppdp-2010-paper.pdf>
|      <http://hackage.haskell.org/package/records>
The story is summarised at
       http://hackage.haskell.org/trac/ghc/wiki/Records

First-class labels are one point in the vast swamp of competing and overlapping proposals for records.  I think they are summarise here:
       http://hackage.haskell.org/trac/ghc/wiki/ExtensibleRecords
I am unsure which of this list of proposals you are referring to. The URL you quote is this
       http://hackage.haskell.org/trac/haskell-prime/wiki/FirstClassLabels
but it doesn't seem to actually contain a design, merely some options for a design that is implicit.  If you do have a design you advocate, it would be good to add it to the list at
       http://hackage.haskell.org/trac/ghc/wiki/ExtensibleRecords
perhaps explaining which of the other members of the list it subsumes.

Because there are so many proposals I have not gone ahead with any of them.  The most recent thread, articulated at
       http://hackage.haskell.org/trac/ghc/wiki/Records
is to ask what is the *smallest change* that would solve the *most pressing problem*, namely the inability to use the same field name in different records.  First class labels is (I assume) much more ambitious.  But maybe not.

Anything you can do to bring clarity to the swamp, by editing the above two pages, would be a great service to the community.  At the moment, we are stuck in an infinite loop.

Simon

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