[ghc-steering-committee] Proposal #302: `\of` (New Shepherd: Simon PJ)

[Alejandro Serrano Mena]

 Dear all,

To be honest, I’m still trying to make up my mind about this. If we were to
accept the proposal, I think option (1) is the best one, since it otherwise
`\case` would have a different behaviour depending on whether you have
-XLambdaCase or -XExtendedLambdaCase on.

Having said so, the words of Simon M. and Richard resonate with me: do we
really want \case, \cases, if|, all in the language?
- I would prefer one single way to do stuff, let’s say having a `cases …
of` which also works as case, if|… and then a \cases for lambdas;
- but this is not the world we live in! We already have those things, and
this would be yet another small syntactic addition, so we need to think
about whether the language is becoming too big.

So right now I’m in favor of option (X), reject the proposal.

Regards,
Alejandro

El 24 jun 2021 12:52:10, Simon Peyton Jones via ghc-steering-committee <
ghc-steering-committee at haskell.org> escribió:

> Dear Steering committee
>
> Simon and Joachim have responded, but only those two .  Please reply!
>
> Thanks
>
> Simon
>
>
>
> *From:* ghc-steering-committee <ghc-steering-committee-bounces at haskell.org>
> *On Behalf Of *Simon Peyton Jones via ghc-steering-committee
> *Sent:* 15 June 2021 13:52
> *To:* Joachim Breitner <mail at joachim-breitner.de>;
> ghc-steering-committee at haskell.org
> *Subject:* Re: [ghc-steering-committee] Proposal #302: `\of` (New
> Shepherd: Simon PJ)
>
>
>
> |  I’d like to reassing shepherding of this one.
>
> |
>
> |  It seems to be clear that we want “something like this”, there are many
> ways
>
> |  to skin the cat, so it comes down to opinion and what we need is a
> decision
>
> |  (or a call to votes). As with anything that’s possibly quite
> opinionated,
>
> |  it’s good to have an authorative voice, so in this case, Simon PJ.
>
> |
>
> |  Simon, can you either come up with a “all things considered, I think
> this
>
> |  variant is the (narrowly) the best” recommendation or, alternative, a
>
> |  “please vote on the following options” verdict?
>
>
>
> OK, to remind everyone
>
>    - Here is the proposal:
>    https://github.com/JakobBruenker/ghc-proposals/blob/patch-1/proposals/0000-lambda-layout.md
>    <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FJakobBruenker%2Fghc-proposals%2Fblob%2Fpatch-1%2Fproposals%2F0000-lambda-layout.md&data=04%7C01%7Csimonpj%40microsoft.com%7C0903e8fd7cbe4aadc88b08d92ffc71d2%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637593584027236069%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=DNZOpilyGrWdTDQyaqEgf1orDNQNX9ZwbMwmGYAk64g%3D&reserved=0>
>    - Here is the discussion:
>    https://github.com/ghc-proposals/ghc-proposals/pull/302
>    <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F302&data=04%7C01%7Csimonpj%40microsoft.com%7C0903e8fd7cbe4aadc88b08d92ffc71d2%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637593584027246062%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=LXuEVBuMxQlbF0elOS2792K5avMW3SeIYEuEDyyFmmo%3D&reserved=0>
>
>
>
> 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.
>
>
>
> The proposal offers four possible syntactic options.  After reviewing, I
> propose to discard (2) and (3) leaving these alternatives
>
>
>
>    - *Option (1)    *\cases { p1 p2 -> rhs1; q1 q2 -> rhs2 }
>
>
>    - Lives alongside \case, but allows multiple patterns
>       - Other keywords are possible, but I think it must be a variant on
>       \case
>
>
>    - *Option (4)*   Same, but use \case as the keyword
>
>
>    - Incompatible with existing \case => extended transition period,
>       unhappy users
>       - \case { (Just x) -> rhs1; Nothing -> rhs2 } will require parens
>       forever, which in the common case of a one argument lambda see clunky.
>
>
>    - *Option (X).*  Reject the proposal.
>
>
>
> 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.
>
> I think we’ll end up having to vote on this, which is fine when it’s a
> judgement call about syntax.   But first:
>
>    - *Are there any other alternatives you strongly want on the ballot?*
>
> I say “strongly” because I don’t want to open up a big new debate… we at
> the stage of trying to narrow options.
>
> Thanks
>
> Simon
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