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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:36.0pt">
Does anyone remember the justification of not having unlifted or open kinds in the source language?<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">They aren’t in the source language because they are a gross hack, with many messy consequences. Particularly the necessary sub-kinding,
and the impact on inference. I’m not proud of it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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";color:#1F497D;mso-fareast-language:EN-US">But I do have a plan. Namely to use polymorphism. Currently we have<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"> kinds k ::= * | # | ? | k1 -> k2 | ...<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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";color:#1F497D;mso-fareast-language:EN-US">Instead I propose<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"> kinds k ::= TYPE bx | k1 -> k2 | ....<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"> boxity bx ::= BOXED | UNBOXED | bv<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">where bv is a boxity variable<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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";color:#1F497D;mso-fareast-language:EN-US">So
<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US"><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:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">* = TYPE BOXED<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:#1F497D;mso-fareast-language:EN-US"><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:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"># = TYPE UNBOXED<o:p></o:p></span></p>
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</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">? = TYPE bv<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">Now error is polymorphic:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"> error :: forall bv. forall (a:TYPE bv). String -> a<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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";color:#1F497D;mso-fareast-language:EN-US">And now everything will work out smoothly I think. And it should be reasonably easy to expose in the source language.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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";color:#1F497D;mso-fareast-language:EN-US">All that said, there’s never enough time to do these things.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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";color:#1F497D;mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;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""> Glasgow-haskell-users [mailto:glasgow-haskell-users-bounces@haskell.org]
<b>On Behalf Of </b>Conal Elliott<br>
<b>Sent:</b> 16 April 2014 18:01<br>
<b>To:</b> Richard Eisenberg<br>
<b>Cc:</b> glasgow-haskell-users@haskell.org<br>
<b>Subject:</b> Re: Concrete syntax for open type kind?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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Oops! I was reading ParserCore.y, instead of Parser.y.pp. Thanks.<br>
<br>
Too bad it's not possible to replicate this type interpretation of `error` and `undefined`. I'm doing some Core transformation, and I have a polymorphic function (reify) that I want to apply to expressions of lifted and unlifted types, as a way of structuring
the transformation. When my transformation gets to unlifted types, the application violates the *-kindedness of my polymorphic function. I can probably find a way around. Maybe I'll build the kind-incorrect applications and then make sure to transform them
away in the end. Currently, the implementation invokes `error`.<br>
<br>
Does anyone remember the justification of not having unlifted or open kinds in the source language?<o:p></o:p></p>
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-- Conal<o:p></o:p></p>
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<o:p> </o:p></p>
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On Tue, Apr 15, 2014 at 5:09 PM, Richard Eisenberg <<a href="mailto:eir@cis.upenn.edu" target="_blank">eir@cis.upenn.edu</a>> wrote:<o:p></o:p></p>
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What version of the GHC code are you looking at? The parser is currently stored in compiler/parser/Parser.y.pp (note the pp) and doesn’t have these lines. As far as I know, there is no way to refer to OpenKind from source.<o:p></o:p></p>
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<o:p> </o:p></p>
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You’re absolutely right about the type of `undefined`. `undefined` (and `error`) have magical types. GHC knows that GHC.Err defines an `undefined` symbol and gives it its type by fiat. There is no way (I believe) to reproduce this behavior.<o:p></o:p></p>
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<o:p> </o:p></p>
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If you have -fprint-explicit-foralls and -fprint-explicit-kinds enabled, quantified variables of kind * are not given kinds in the output. So, the lack of a kind annotation tells you that `a`’s kind is *. Any other kind (assuming these flags) would be printed.<o:p></o:p></p>
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<o:p> </o:p></p>
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I hope this helps!<o:p></o:p></p>
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Richard<o:p></o:p></p>
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<o:p> </o:p></p>
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On Apr 15, 2014, at 7:39 PM, Conal Elliott <<a href="mailto:conal@conal.net" target="_blank">conal@conal.net</a>> wrote:<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
I see ‘#’ for unlifted and ‘?’ for open kinds in compiler/parser/Parser.y: <o:p></o:p></p>
<pre style="margin-left:30.0pt"><code>akind :: { IfaceKind }<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code> : '*' { ifaceLiftedTypeKind } <o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code> | '#' { ifaceUnliftedTypeKind }<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code> | '?' { ifaceOpenTypeKind }<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code> | '(' kind ')' { $2 }<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code><o:p> </o:p></code></pre>
<pre style="margin-left:30.0pt"><code>kind :: { IfaceKind }<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code> : akind { $1 }<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code> | akind '->' kind { ifaceArrow $1 $3 }</code><o:p></o:p></pre>
<p>However, I don’t know how to get GHC to accept ‘#’ or ‘?’ in a kind annotation. Are these kinds really available to source programs.<o:p></o:p></p>
<p>I see that undefined has an open-kinded type:<o:p></o:p></p>
<pre style="margin-left:30.0pt"><code>*Main> :i undefined<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code>undefined :: forall (a :: OpenKind). a -- Defined in ‘GHC.Err’</code><o:p></o:p></pre>
<p>Looking in the GHC.Err source, I just see the following:<o:p></o:p></p>
<pre style="margin-left:30.0pt"><code>undefined :: a<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code>undefined = error "Prelude.undefined"</code><o:p></o:p></pre>
<p>However, if I try similarly,<o:p></o:p></p>
<pre style="margin-left:30.0pt"><code>q :: a<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code>q = error "q"</code><o:p></o:p></pre>
<p>I don’t see a similar type:<o:p></o:p></p>
<pre style="margin-left:30.0pt"><code>*X> :i q<o:p></o:p></code></pre>
<pre style="margin-left:30.0pt"><code>q :: forall a. a -- Defined at ../test/X.hs:12:1</code><o:p></o:p></pre>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">I don't know what kind 'a' has here, nor how to find out.<o:p></o:p></p>
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<p class="MsoNormal">-- Conal<o:p></o:p></p>
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