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<p class="MsoPlainText">| I’d like to reassing shepherding of this one.<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| It seems to be clear that we want “something like this”, there are many ways<o:p></o:p></p>
<p class="MsoPlainText">| to skin the cat, so it comes down to opinion and what we need is a decision<o:p></o:p></p>
<p class="MsoPlainText">| (or a call to votes). As with anything that’s possibly quite opinionated,<o:p></o:p></p>
<p class="MsoPlainText">| it’s good to have an authorative voice, so in this case, Simon PJ.<o:p></o:p></p>
<p class="MsoPlainText">| <o:p></o:p></p>
<p class="MsoPlainText">| Simon, can you either come up with a “all things considered, I think this<o:p></o:p></p>
<p class="MsoPlainText">| variant is the (narrowly) the best” recommendation or, alternative, a<o:p></o:p></p>
<p class="MsoPlainText">| “please vote on the following options” verdict?<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><span style="font-family:"Calibri",sans-serif">OK, to remind everyone<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="mso-list:l2 level1 lfo1"><span style="font-family:"Calibri",sans-serif">Here is the proposal:
<a href="https://github.com/JakobBruenker/ghc-proposals/blob/patch-1/proposals/0000-lambda-layout.md">
https://github.com/JakobBruenker/ghc-proposals/blob/patch-1/proposals/0000-lambda-layout.md</a><o:p></o:p></span></li><li class="MsoPlainText" style="mso-list:l2 level1 lfo1"><span style="font-family:"Calibri",sans-serif">Here is the discussion:
<a href="https://github.com/ghc-proposals/ghc-proposals/pull/302">https://github.com/ghc-proposals/ghc-proposals/pull/302</a><o:p></o:p></span></li></ul>
<p class="MsoPlainText"><span style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="font-family:"Calibri",sans-serif">The basic idea is to extend to lambda all the facilities that you get with function definitions, especially multiple patterns and guards. This seems clearly a good idea, whose only obstacle
is syntactic. There are no conceptual or specification challenges. The only point at issue is that of concrete syntax.<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="font-family:"Calibri",sans-serif">The proposal offers four possible syntactic options. After reviewing, I propose to discard (2) and (3) leaving these alternatives<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo4"><b>Option (1)
</b>\cases { p1 p2 -> rhs1; q1 q2 -> rhs2 }<o:p></o:p></li><ul style="margin-top:0cm" type="circle">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level2 lfo4">Lives alongside \case, but allows multiple patterns<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level2 lfo4">Other keywords are possible, but I think it must be a variant on \case<o:p></o:p></li></ul>
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo4"><b>Option (4)</b> Same, but use \case as the keyword<o:p></o:p></li><ul style="margin-top:0cm" type="circle">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level2 lfo4">Incompatible with existing \case => extended transition period, unhappy users<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level2 lfo4">\case { (Just x) -> rhs1; Nothing -> rhs2 } will require parens forever, which in the common case of a one argument lambda see clunky.<o:p></o:p></li></ul>
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo4"><b>Option (X).</b> Reject the proposal.<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Personally I favour (1). I’m relaxed about having multiple ways of saying the thing (think of let vs where), and I see no harm provided the two constructs look and behave the same. I’ve decided I like \cases precisely because it’s the
plural of \case, which is exactly what is going on.<o:p></o:p></p>
<p class="MsoNormal">I think we’ll end up having to vote on this, which is fine when it’s a judgement call about syntax. But first:<o:p></o:p></p>
<ul style="margin-top:0cm" type="circle">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l3 level1 lfo5"><b>Are there any other alternatives you
<i>strongly</i> want on the ballot?<o:p></o:p></b></li></ul>
<p class="MsoNormal">I say “strongly” because I don’t want to open up a big new debate… we at the stage of trying to narrow options.<o:p></o:p></p>
<p class="MsoNormal">Thanks<o:p></o:p></p>
<p class="MsoNormal">Simon<o:p></o:p></p>
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