<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman","serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p
{mso-style-priority:99;
mso-margin-top-alt:auto;
margin-right:0cm;
mso-margin-bottom-alt:auto;
margin-left:0cm;
font-size:12.0pt;
font-family:"Times New Roman","serif";}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
.MsoPapDefault
{mso-style-type:export-only;
margin-top:6.0pt;
margin-right:0cm;
margin-bottom:6.0pt;
margin-left:0cm;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-GB" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">David<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">If you want to suggest a couple of possible alternative 20-min slots in work time (London time zone), not Mon-Weds this week, then maybe we can find a mutually
convenient time.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">Do you have reason to suppose that the pattern you describe below is common? That is, if implemented, would it make a big difference to programs we care about?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt">
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif""> David Feuer [mailto:david.feuer@gmail.com]
<br>
<b>Sent:</b> 20 October 2014 13:58<br>
<b>To:</b> Simon Peyton Jones<br>
<b>Cc:</b> ghc-devs<br>
<b>Subject:</b> Re: Help understanding Specialise.lhs<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
To be super-clear about at least one aspect: I don't want Tidy Core to ever contain something that looks like this:<br>
<br>
GADTTest.potato<br>
:: <a href="http://GHC.Types.Int" target="_blank">GHC.Types.Int</a> -> GADTTest.Silly
<a href="http://GHC.Types.Int" target="_blank">GHC.Types.Int</a> -> <a href="http://GHC.Types.Int" target="_blank">
GHC.Types.Int</a><br>
GADTTest.potato =<br>
\ (x_asZ :: <a href="http://GHC.Types.Int" target="_blank">GHC.Types.Int</a>)<br>
(ds_dPR :: GADTTest.Silly <a href="http://GHC.Types.Int" target="_blank">GHC.Types.Int</a>) -><br>
case ds_dPR of _ { GADTTest.Silly $dNum_aLV ds1_dPS -><br>
GHC.Num.+ @ <a href="http://GHC.Types.Int" target="_blank">GHC.Types.Int</a> $dNum_aLV x_asZ x_asZ<br>
}<o:p></o:p></p>
</div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Here we see GHC.Num.+ applied to <a href="http://GHC.Types.Int" target="_blank">GHC.Types.Int</a> and $dNum_aLV. We therefore know that $dNum_aLV must be GHC.Num.$fNumInt, so GHC.Num.+ can eat these arguments and produce GHC.Num.$fNumInt_$c+. But for some
reason, GHC fails to recognize and exploit this fact! I would like help understanding why that is, and what I can do to fix it.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
<o:p> </o:p></p>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
On Mon, Oct 20, 2014 at 7:53 AM, David Feuer <<a href="mailto:david.feuer@gmail.com" target="_blank">david.feuer@gmail.com</a>> wrote:<o:p></o:p></p>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm">
<p>On Oct 20, 2014 5:05 AM, "Simon Peyton Jones" <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<br>
> I’m unclear what you are trying to achieve with #9701. I urge you to write a clear specification that we all agree about before burning cycles hacking code.<o:p></o:p></p>
<p>What I'm trying to achieve is to make specialization work in a situation where it currently does not. It appears that when the type checker determines that a GADT carries a certain dictionary, the specializer happily uses it *even once the concrete type
is completely known*. What we would want to do in that case is to replace the use of the GADT-carried dictionary with a use of the known dictionary for that type.<o:p></o:p></p>
<p>> There are a lot of comments at the top of Specialise.lhs. But it is, I’m afraid, a tricky pass. I could skype.<o:p></o:p></p>
<p>I would appreciate that. What day/time are you available?<o:p></o:p></p>
</blockquote>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</body>
</html>