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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Johan<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">I think this would be a very interesting thing to do. But it would be a big project. It is absolutely not routine work.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo3"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Strict Core is not just a little wibble. It is a pretty big change.
<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l2 level2 lfo3">
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</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">It embraces multiple values. These aren’t the same as unboxed tuples because they include types, thus <Int, 7, ‘x’><o:p></o:p></span></p>
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</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">It has multiple binders, in which early ones scope over later ones<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l2 level2 lfo3">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">It has both ‘let’ and ‘valrec’.<o:p></o:p></span></p>
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</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">I’m not sure how ANF-ised it should be<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l2 level2 lfo3">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Courier New";color:#1F497D"><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">I am unsure about the interaction with user-written RULES<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo3"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">It needs to be extended with coercions and casts. I don’t think this would be too hard<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo3"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">How do unboxed tuples fit in?<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo3"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">I’m not certain whether delay/force should be done via encoding (as the paper suggests) or expressed directly.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo3"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Programs would get bigger<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">So it would force re-examination of many things. In effect we’d go back three steps in order to position ourselves to move forward four or more. The benefits
would, I think, ultimately be substantial, but it’d take a while for them to manifest themselves.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">If you wanted to undertake it I’d be happy to play an advisory role. It’s really hard to guess how long it’d take. To get to something that stumbles along:
weeks not days. To get to something that routinely out-performs the baseline: months not weeks.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Step 0 should be to write a detailed specification, based on the paper, so that we all understand the language you are implementing. Richards docs/core-spec/
is a model.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></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""> Johan Tibell [mailto:johan.tibell@gmail.com]
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<b>Sent:</b> 02 May 2013 17:30<br>
<b>To:</b> Simon Peyton-Jones; Max Bolingbroke<br>
<b>Cc:</b> ghc-devs@haskell.org<br>
<b>Subject:</b> Implementing Strict Core<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi Simon and Max,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I've been thinking about Strict Core quite a bit lately. I'd like to take a stab at implementing it in GHC, if feasible. My motivations for implementing Strict Core are<o:p></o:p></p>
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<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
generating faster code in a more robust manner, and<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
implementing strictness annotations at the type level in Haskell itself*.<o:p></o:p></li></ul>
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<p class="MsoNormal">Now, I don't know how much work this will be. What's you best time estimate (say, if you would do it vs if I would do it)?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">My plan would roughly be as follows:<o:p></o:p></p>
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<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Create a branch to develop on.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Temporarily delete all the non-essential Core2Core transformations. This will let us get to a place where we have a functional compiler using Strict Core more quickly.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Change CoreSyn.Expr to be Strict Core.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Plumb the changes through the compiler until it compiles (and passes the tests) again.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Once all tests pass, re-add all the Core2Core passes and make them use Strict Core.<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
Rebase the commits so they can be merged nicely into the main branch.<o:p></o:p></li></ol>
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<p class="MsoNormal">How does that sound?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">* I think this could be one of the most important changes in a long time to help Haskell in the "real world". It gives us a better way to talk about strictness than we have today, reducing time spent on chasing down space leaks. One we
have strictness annotations in type, we could experiment with a Strict language pragma to make a whole module call-by-value.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Cheers,<o:p></o:p></p>
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<p class="MsoNormal">Johan<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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