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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">newtype T = MkT Int#<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">Provided T :: # (i.e. unlifted), I don’t think this would be too hard. That is, you can give a new name (via newtype) to an unlifted type like Int#, Float#, Double#
etc.<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">Worth a wiki page and a ticket.<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>
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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-devs [mailto:ghc-devs-bounces@haskell.org]
<b>On Behalf Of </b>Edward Kmett<br>
<b>Sent:</b> 21 December 2015 09:10<br>
<b>To:</b> Ömer Sinan Ağacan <omeragacan@gmail.com><br>
<b>Cc:</b> ghc-devs <ghc-devs@haskell.org><br>
<b>Subject:</b> Re: Kinds of type synonym arguments<o:p></o:p></span></p>
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<p class="MsoNormal">I brought up the subject of allowing newtypes in kind # (or even in any kind that ends in * or # after a chain of ->'s to get more powerful Coercible instances) at ICFP this year and Simon seemed to think it'd be a pretty straightforward
modification to the typechecker.<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 confess, he's likely waiting for me to actually sit down and give the idea a nice writeup. ;)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">This would be good for many things, especially when it comes to improving the type safety of various custom c-- tricks.<o:p></o:p></p>
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<p class="MsoNormal">-Edward<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Sun, Dec 20, 2015 at 2:14 PM, Ömer Sinan Ağacan <<a href="mailto:omeragacan@gmail.com" target="_blank">omeragacan@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">I have another related question: What about allowing primitive types<br>
in newtypes?<br>
<br>
λ:4> newtype Blah1 = Blah1 Int<br>
λ:5> newtype Blah2 = Blah2 Int#<br>
<br>
<interactive>:5:23: error:<br>
• Expecting a lifted type, but ‘Int#’ is unlifted<br>
• In the type ‘Int#’<br>
In the definition of data constructor ‘Blah2’<br>
In the newtype declaration for ‘Blah2’<br>
<br>
Ideally second definition should be OK, and kind of Blah2 should be #. Is this<br>
too hard to do?<o:p></o:p></p>
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2015-12-16 17:22 GMT-05:00 Richard Eisenberg <<a href="mailto:eir@cis.upenn.edu">eir@cis.upenn.edu</a>>:<br>
><br>
> On Dec 16, 2015, at 2:06 PM, Ömer Sinan Ağacan <<a href="mailto:omeragacan@gmail.com">omeragacan@gmail.com</a>> wrote:<br>
>><br>
>> In any case, this is not that big deal. When I read the code I thought this<br>
>> should be a trivial change but apparently it's not.<br>
><br>
> No, it's not. Your example (`f :: (Int#, b) -> b`) still has an unboxed thing in a boxed tuple. Boxed tuples simply can't (currently) hold unboxed things. And changing that is far from trivial. It's not the polymorphism that's the problem -- it's the unboxed
thing in a boxed tuple.<br>
><br>
> Richard<br>
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<p class="MsoNormal"><o:p> </o:p></p>
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