<div dir="ltr"><div>I voted to park, as per Simon's recommendation (although if it comes up again I would be against unless it can be made a non-breaking change perhaps by using Adam's suggestion of pattern synonyms).<br></div><div><br></div><div>Cheers</div><div>Simon<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, 2 Apr 2024 at 17:25, Simon Peyton Jones <<a href="mailto:simon.peytonjones@gmail.com">simon.peytonjones@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_default" style="font-family:tahoma,sans-serif">Dear GHC Steering Committee</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">
<span>
Vlad proposes to amend <a href="https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0425-decl-invis-binders.rst" target="_blank">proposal #425 </a>to permit more wildcard binder forms in type declarations:<br><div style="margin-left:40px"> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/641" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/641</a></div><div style="margin-left:40px"><br></div>See my mail below. I recommend, fairly strongly, to park this until there is evidence of need.</span></div><div class="gmail_default" style="font-family:tahoma,sans-serif"><ul><li>
<div style="font-family:tahoma,sans-serif" class="gmail_default">it's an unforced change, </div></li><li><div style="font-family:tahoma,sans-serif" class="gmail_default">with no user demand</div></li><li><div style="font-family:tahoma,sans-serif" class="gmail_default">but some real user impact (notably: it will break some TH users)</div></li><li><div style="font-family:tahoma,sans-serif" class="gmail_default">and some implementation cost (modest but very non-zero)</div></li><li><div style="font-family:tahoma,sans-serif" class="gmail_default">aiming to anticipate as-yet-unknown future requirements -- but <a href="https://martinfowler.com/bliki/Yagni.html" target="_blank">YAGNI</a></div></li></ul><div>I think it's time to vote. Please so before Monday morning. Thank you!</div><div><br></div><div>Simon<br></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 21 Mar 2024 at 09:56, Simon Peyton Jones <<a href="mailto:simon.peytonjones@gmail.com" target="_blank">simon.peytonjones@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_default" style="font-family:tahoma,sans-serif">Dear Steering Committee</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">
Vlad proposes to amend <a href="https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0425-decl-invis-binders.rst" target="_blank">proposal #425 </a>to permit more wildcard binder forms in type declarations:<br><div style="margin-left:40px"> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/641" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/641</a></div><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">You may find it easiest to look at <a href="https://github.com/ghc-proposals/ghc-proposals/pull/641/files?short_path=cb2a762#diff-cb2a762676d938436a07317bbd007570b5efdfa00b40763b897ee920694bcbb5" target="_blank">the rich diff</a>.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">This is a pretty small generalisation which would allow</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;margin-left:40px">data T (( (a :: k1) :: k2)) = ...</div><div class="gmail_default" style="font-family:tahoma,sans-serif;margin-left:40px"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">in which the binder has multiple kind signatures and redundant parens. The change is <b>not driven by user need</b>, but rather solely by <b>uniformity</b>: these same forms are permitted in function definitions:</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif;margin-left:40px">f :: forall (a :: k). blah</div><div class="gmail_default" style="font-family:tahoma,sans-serif;margin-left:40px">f @(((a::k1)::k2))) = ...</div><div class="gmail_default" style="font-family:tahoma,sans-serif;margin-left:40px"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">is permitted.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">It imposes a change on Template Haskell syntax too.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">The implementation becomes a bit more complicated; more recursive data types, etc. Nothing hard, but more.<br></div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">It's not a big deal either way. Very few people expressed a view on GitHub. My personal view is that the modest (albeit non-zero) gain does not justify the definite (albeit modest) pain. I would leave this until someone actually wants it.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Vlad argues for future-proofing, but my experience is that an eye to the future is sensible when you are making changes anyway; but making unforced changes solely for the future risks incurring pain now that, when the future comes, turns out to have been a poor investment. We may have correctly anticipated, or we may not.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">So my recommendation is to park this until we get a real user demand.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">It's a perfectly sensible proposal, but adopting it is a judgement call. I'll leave a week for committee responses, and then we can just vote.</div><div class="gmail_default" style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" style="font-family:tahoma,sans-serif">Simon<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 21 Mar 2024 at 08:07, Adam Gundry <<a href="mailto:adam@well-typed.com" target="_blank">adam@well-typed.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear Committee,<br>
<br>
Vlad proposes to amend proposal #425 to permit more wildcard binder <br>
forms in type declarations:<br>
<br>
<a href="https://github.com/ghc-proposals/ghc-proposals/pull/641" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/641</a><br>
<br>
I'd like to nominate Simon PJ as the shepherd.<br>
<br>
Please guide us to a conclusion as outlined in<br>
<a href="https://github.com/ghc-proposals/ghc-proposals#committee-process" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals#committee-process</a><br>
<br>
Cheers,<br>
<br>
Adam<br>
<br>
<br>
-- <br>
Adam Gundry, Haskell Consultant<br>
Well-Typed LLP, <a href="https://www.well-typed.com/" rel="noreferrer" target="_blank">https://www.well-typed.com/</a><br>
<br>
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