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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Would it be worth revising the proposal to incorporate the thinking in this thread, including the answers to Iavor’s questions?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-steering-committee <ghc-steering-committee-bounces@haskell.org>
<b>On Behalf Of </b>Richard Eisenberg<br>
<b>Sent:</b> 17 April 2018 20:22<br>
<b>To:</b> Iavor Diatchki <iavor.diatchki@gmail.com><br>
<b>Cc:</b> ghc-steering-committee@haskell.org; Joachim Breitner <mail@joachim-breitner.de><br>
<b>Subject:</b> Re: [ghc-steering-committee] Proposal: Embrace Type in Type<o:p></o:p></span></p>
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<p class="MsoNormal">Hi Iavor,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">See my answers below.<o:p></o:p></p>
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<p class="MsoNormal">On Apr 17, 2018, at 2:23 PM, Iavor Diatchki <<a href="mailto:iavor.diatchki@gmail.com">iavor.diatchki@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hello,<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 have a couple of pragmatic questions:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">1. To "fix" my code so that it is compatible with this change I need to do the following:<o:p></o:p></p>
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<p class="MsoNormal"> 1. Whenever I have kind signatures mentioning `*`, replace `*` with `Type`<o:p></o:p></p>
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<p class="MsoNormal"> 2. Import `Data.Kind(Type)`<o:p></o:p></p>
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<p class="MsoNormal"> 3. Resolve conflicts involving existing datatypes named `Type`.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">2. If my code has all of the properties below, then it will break as soon as this change is adopted, so I have to fix it in some way straight away:<o:p></o:p></p>
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<p class="MsoNormal"> 1. uses `*` is a binary type operator, and<o:p></o:p></p>
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<p class="MsoNormal"> 2. uses `*` in kind signatures, and<o:p></o:p></p>
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<p class="MsoNormal"> 3. uses the `PolyKinds` language extension.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">3. If my code does not have the properties in (2) but uses `*` in kind signatures, it will continue to work for 2 GHC releases, but then it will break, so I should do (1) sometime before.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Is my understanding correct?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Not quite.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">First off, this proposal *does not* propose deprecating *. Earlier versions may have, but that's no longer the case. There is no concrete plan to remove * at any point in the future. Any movement to do so would be years in the future, I
imagine.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In point (1), "compatible" is unclear. I think you mean "compatible forever" as opposed to "compatible today". The changes you suggest in (1) are what you would have to do if we ever decide to deprecate *.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">For point (2), the conditions are slightly different than what you write. They should be<o:p></o:p></p>
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<p class="MsoNormal"> a. enables -XTypeOperators<o:p></o:p></p>
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<p class="MsoNormal"> b. uses `*` in kind signatures<o:p></o:p></p>
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<p class="MsoNormal">Modules that have these features will have to make an immediate change. They could either do the changes under your point (1) or enable -XStarIsType.<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 only part of this proposal that mentions something that will happen in 2 releases is that -XTypeOperators will stop implying -XNoStarIsType in two releases. That particular aspect of this is up for debate, of course.<o:p></o:p></p>
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<p class="MsoNormal">Richard<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-Iavor<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 Mon, Apr 16, 2018 at 10:46 AM Joachim Breitner <<a href="mailto:mail@joachim-breitner.de">mail@joachim-breitner.de</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi,<br>
<br>
Am Montag, den 16.04.2018, 11:55 -0400 schrieb Richard Eisenberg:<br>
> An alternative that hasn't been suggested so far is to have<br>
> -XStarIsType control the pretty-printer as well as the parser. Simon<br>
> PJ and I discussed this this morning, thinking it was a good idea.<br>
> Upon further consideration, my preference would be to bite the bullet<br>
> and just switch to printing Type always, but I'm not really against<br>
> the print-*-with-XStarIsType idea.<br>
<br>
I’m with Simon here. We have, I believe, precedence where error<br>
messages are affected by the language extension in scope, so this might<br>
satisfy the principle of least surprise, and also cause the least<br>
contention among our users.<br>
<br>
We can still apply this rule when `-XNoStarIsType`:<br>
<br>
> One slightly separate question is what to print. The proposal<br>
> currently suggests to print Type. There was concern in this thread<br>
> that it would be printed fully-qualified, but I like Joachim's<br>
> suggestion in the last known email in this thread to special-case<br>
> printing of Type; even if it's not imported, it would print as Type,<br>
> not Data.Kind.Type. (Unless some other Type were in scope.) It is<br>
> also easy to teach GHC to print a bespoke warning when a user writes<br>
> Type when it is out of scope, telling them to import Data.Kind.<br>
<br>
The proposal currently does not state which modules export Type. I can<br>
infer from the text that it is Data.Kind, but this could be made<br>
explicit. Also, the proposal should state whether it is re-exported<br>
from Prelude or not (I assume it is not).<br>
<br>
Cheers,<br>
Joachim<br>
<br>
-- <br>
Joachim Breitner<br>
<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a><br>
<a href="http://www.joachim-breitner.de/" target="_blank">http://www.joachim-breitner.de/</a><br>
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<p class="MsoNormal">_______________________________________________<br>
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