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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">I agree. You might need to write up the notes below into a publicly-readable form, but that should not be hard.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">(In general, for all our “verdicts” I think we should write up a rationale for the author and others to read.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></a></p>
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<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"> ghc-steering-committee [mailto:ghc-steering-committee-bounces@haskell.org]
<b>On Behalf Of </b>Richard Eisenberg<br>
<b>Sent:</b> 13 March 2017 20:16<br>
<b>To:</b> ghc-steering-committee@haskell.org<br>
<b>Subject:</b> [ghc-steering-committee] Eval proposal (#27)<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am shepherding the Eval class proposal, #29. Very, very briefly, this proposes to bring back<o:p></o:p></p>
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<p class="MsoNormal">> class Eval a where<o:p></o:p></p>
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<p class="MsoNormal">> seq :: a -> b -> b<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The author of the proposal cites some motivation, but a recurring theme in the discussion is that this is just the first step toward some ill-defined promised land. The author himself admits he’s not quite sure what the promised land holds,
other than safety under eta-expansion, along with a restoration of parametricity.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The proposal includes a new extension, on by default, -XUniversalEval, that adds Eval constraints in many places. Even with -XUniversalEval, however, this extension is not fully backward compatible, in corner cases (seq’ing in a class method;
polymorphic recursion, possibly higher-rank types.<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 move to reject this proposal. The author (along with a few others) argues that this brings some nice theoretical properties to Haskell. I agree here. But the cost doesn’t seem to be worth the benefit, especially considering that this
may be the first step toward some ill-specified goal. In short, while I might be happy enough with the language proposed here, I don’t relish the idea of getting from where we are to that language, and I don’t think the gain is worth the pain.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">You can see the PR here: <a href="https://github.com/ghc-proposals/ghc-proposals/pull/27">https://github.com/ghc-proposals/ghc-proposals/pull/27</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Richard<o:p></o:p></p>
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