<div>The semantics of Frege's records are layed out in its manual [1] in the following sections:</div><div><div>4.2.1 Algebraic Data type Declaration - Constructors with labeled fields</div></div><div>3.2 Primary Expression</div>
<div><br></div><div>The Frege record system explanation is the first one that I could read and immediately understand (oh, it just creates a namespace!). Perhaps this is just in part because it was better explained. But I think it is also because desugaring records to a library is a very complicated proposition, whereas taking the same library concept but baking it into the compiler and making simple language modifications is actually much more straightforward to understand.</div>
<div><br></div><div>Many of the built-in record proposals seem more ambitious (create a new record from an existing one, generalize in some other direction). More power or generalization could be very useful, but it can wait for later - Haskell's records are glaringly bad because they lack name-spacing.</div>
<div><br></div><div>I think one of the problems being faced with improving records is a false choice between a quick but hacky library desugaring or a major "Extensible" records built into the compiler. What I am proposing is that (unless someone proposes a great desugaring solution) we make it the immediate goal to have records built into the compiler, but done in the simplest (perhaps least "Extensible") way that just accomplishes name-spacing.</div>
<div><br></div><div>[1] <a href="http://code.google.com/p/frege/downloads/detail?name=Language-202.pdf">http://code.google.com/p/frege/downloads/detail?name=Language-202.pdf</a><br><br><div class="gmail_quote">On Tue, Dec 27, 2011 at 8:32 AM, Greg Weber <span dir="ltr"><<a href="mailto:greg@gregweber.info">greg@gregweber.info</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">The original goal was to come up with a simple solution. Perhaps that goal is unattainable, or at least attaining it has much higher cost than we had hoped. If that is the case we must take a step back and look at changing how things are done currently. Perhaps the approach that a record label becomes a global module function is just not feasible.<div>
<p>In the <a href="http://code.google.com/p/frege" target="_blank">Frege</a> (a Haskell with some differences implementation on the JVM) language every data type is at the same time a namespace.</p><p style="text-align:left">
* the function that accesses field x of data type T is T.x</p>
<p style="text-align:left">* If a::T then a.x = T.x a</p><p style="text-align:left">* the function that updates field x of data type T is T.{x=}</p><p style="text-align:left">* the function that sets field x in a T to 42 is T.{x=42}</p>
<p style="text-align:left">* If a::T then a.{x=} and a.{x=42} are valid</p><p style="text-align:left">* the function that changes field x of a T by applying some function to it is T.{x <-}</p><p style="text-align:left">
* T.{x?} is a function that returns true iff the argument was constructed with a data constructor that has field x.</p><div>In the Opa language a Module is in fact a Record specially marked as a module.</div><div><br></div>
<div>What do you think of the Frege system?</div><div><div></div><div class="h5"><br><div class="gmail_quote">On Fri, Dec 23, 2011 at 2:40 PM, Greg Weber <span dir="ltr"><<a href="mailto:greg@gregweber.info" target="_blank">greg@gregweber.info</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I am willing to help on this as much as I can. Unfortunately I don't think you want me to lead the discussion or make decisions on this - many of these discussions seem over my head. I will continue to study them though and see if the sink in more.<div>
<br></div><div>I do think almost all of these proposals want a dot selector, so it is a good idea for Haskell to require the normal function (composition) dot to have spaces around it - should this be brought to the Haskell Prime committee?</div>
<div><br></div><div><font color="#888888">Greg Weber</font><div><div></div><div><br><br><div class="gmail_quote">On Fri, Dec 23, 2011 at 1:52 PM, Simon Peyton-Jones <span dir="ltr"><<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>></span> wrote:<br>
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<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:14.0pt">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 :)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
</div><p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Yes, they are stalled again. The “simple solution” turned out to be not simple. I wrote it up at length in
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">
<a href="http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields" target="_blank">
http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields</a><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">There are various unsatisfactory aspects of the proposal, particularly concerning record update. I am not sure how to resolve them.
<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Meanwhile, AntC has put forth another proposal that I have not had time to look at in detail.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><a href="http://www.haskell.org/pipermail/glasgow-haskell-users/2011-December/021298.html" target="_blank">http://www.haskell.org/pipermail/glasgow-haskell-users/2011-December/021298.html</a><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><b><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">What this needs is someone (not me) to lead the discussion and try to make sure it makes progress</span></b><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">.
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!<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Simon<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Greg Weber [mailto:<a href="mailto:greg@gregweber.info" target="_blank">greg@gregweber.info</a>]
<br>
<b>Sent:</b> 09 December 2011 19:38<br>
<b>To:</b> Simon Peyton-Jones<br>
<b>Cc:</b> Wolfgang Jeltsch; <a href="mailto:glasgow-haskell-users@haskell.org" target="_blank">glasgow-haskell-users@haskell.org</a></span></p><div><br>
<b>Subject:</b> Re: Records in Haskell<u></u><u></u></div><p></p>
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<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">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 :)<u></u><u></u></p>
<div><div></div><div>
<div>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">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?<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Mon, Nov 7, 2011 at 10:21 AM, Simon Peyton-Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<u></u><u></u></p>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">| would inclusion of such a record system into GHC mean that plans for<br>
| first-class labels (<<a href="http://tinyurl.com/7fppj32" target="_blank">http://tinyurl.com/7fppj32</a>>) are abandoned? That<br>
| would be a pity, since first-class labels are very useful to implement<br>
| record systems that go beyond what the abovementioned record system<br>
| provides. See, for example, my work on records:<br>
| <<a href="http://www.informatik.tu-cottbus.de/~jeltsch/research/ppdp-2010-paper.pdf" target="_blank">http://www.informatik.tu-cottbus.de/~jeltsch/research/ppdp-2010-paper.pdf</a>><br>
| <<a href="http://hackage.haskell.org/package/records" target="_blank">http://hackage.haskell.org/package/records</a>><u></u><u></u></p>
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<p class="MsoNormal">The story is summarised at<br>
<a href="http://hackage.haskell.org/trac/ghc/wiki/Records" target="_blank">http://hackage.haskell.org/trac/ghc/wiki/Records</a><br>
<br>
First-class labels are one point in the vast swamp of competing and overlapping proposals for records. I think they are summarise here:<br>
<a href="http://hackage.haskell.org/trac/ghc/wiki/ExtensibleRecords" target="_blank">http://hackage.haskell.org/trac/ghc/wiki/ExtensibleRecords</a><br>
I am unsure which of this list of proposals you are referring to. The URL you quote is this<br>
<a href="http://hackage.haskell.org/trac/haskell-prime/wiki/FirstClassLabels" target="_blank">http://hackage.haskell.org/trac/haskell-prime/wiki/FirstClassLabels</a><br>
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<br>
<a href="http://hackage.haskell.org/trac/ghc/wiki/ExtensibleRecords" target="_blank">http://hackage.haskell.org/trac/ghc/wiki/ExtensibleRecords</a><br>
perhaps explaining which of the other members of the list it subsumes.<br>
<br>
Because there are so many proposals I have not gone ahead with any of them. The most recent thread, articulated at<br>
<a href="http://hackage.haskell.org/trac/ghc/wiki/Records" target="_blank">http://hackage.haskell.org/trac/ghc/wiki/Records</a><br>
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.<br>
<br>
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.<br>
<span style="color:#888888"><br>
Simon</span><u></u><u></u></p>
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