[ghc-steering-committee] Record dot notation

[Vitaly Bragilevsky]

Hello,

While I was leaning towards rejecting, I've changed my mind.

Simon's idea that this proposal brings Haskell closer to
other programming languages in terms of record selection is quite
convincing. I'm next to Iavor finding (4) easier to explain. I agree with
Joachim that introducing whitespace-sensitivity can be misleading,
especially while explaining this new notation to others.

Thus, I prefer:
5 > 4 > 2 > 3 > 1

Vitaly

пт, 7 февр. 2020 г. в 20:13, Simon Peyton Jones via ghc-steering-committee <
ghc-steering-committee at haskell.org>:

> Colleagues
>
> I've been slow on the records front; apologies.
>
> I think Joachim is right: we've discussed a lot of options, but in the
> end much of this is a judgement call with no perfect answers, and it
> now seems simplest to express our judgement through voting. I think
> we are all keen to decide this and move on.
>
> Proposal:
> https://github.com/shayne-fletcher-da/ghc-proposals/blob/record-dot-syntax/proposals/0000-record-dot-syntax.md
> Lengthy discussion:
> https://github.com/ghc-proposals/ghc-proposals/pull/282
>
> Here are the alternatives I propose we vote on.  The first order of
> business is to check that they are all clear; and that I haven't omitted
> a worthy alternative.  Here they are:
>
> 1. Reject the proposal
>
> 2. Naked .x is illegal
>
> 3. Naked .x is a postfix operator, binding exactly
>    like application:  f r .x   means (f r).x
>
> 4. Naked .x is a postfix operator, binding more tightly
>    than application: f r .x   means   f (r.x)
>
> Under all of (2,3,4) I think we are content that
>   - (f r.x) means  (f (r.x))
>   - (.x)    means  (\r -> r.x)
>
> By "naked .x" I mean "not preceded by an identifier (e.g. r.x),
> or an open paren (e.g. (.x)), or a close paren (e.g. (f 3).x)
>
> We could re-open more of this, but I'd prefer to keep it to 1-4.
>
> Let's just check everyone is happy with these alternatives.  Then we can
> vote by putting in rank order, and Joachim can run his STV algorithm.
>
>
> I'm the shepherd for this proposal, so let me add my recommendations.
>
> I strongly urge that we do not adopt (1); that is, we accept the
> proposal in some form.  I have been unhappy with GHC's story for
> records for two decades.  (E.g. Lightweight extensible records for
> Haskell, Haskell Workshop, Paris 1999.)  But the design space is so
> complicated that we never found something that felt "obviously right".
> So we did nothing drastic, and I think that was right.
>
> But there was incremental progress, sketched here:
> https://gitlab.haskell.org/ghc/ghc/wikis/records/overloaded-record-fields
>
> * DuplicateRecordFields lets you have multiple records with the
>   same field name.
> * The HasField class lets us define overloaded record selection
>   and update functions.
>
> The proposal we are now discussing has no type-system component;
> it is *only* about syntactic sugar, allowing you to use dot-notation
> for field selection.
>
> Various extensions about syntax for update were discussed, but no
> longer form part of the proposal; what is left is the core, which
> has a particularly high benefit/cost ratio.
>
> Now, judgements may differ about the importance of syntactic sugar --
> that's why we have a committee with a diversity of views -- but I
> believe that dot-notation for record selection is super-important.
> I've wanted it for ages.  Every other language has it.  We have
> accepted other syntactic sugar with much lower utility.  And
> the dot is already a special case, via qualified names.
>
> I respect the fact that others may differ, but I really think
> think this is worth it.  It would be a crying shame to reject
> this.  Unlike Chris, I don't think anything better is going to
> emerge, however long we wait.
>
> I am more relaxed about 2/3/4.  Personally I hate (4) because
> I don't like *any* notation in which something binds more tightly
> than function application.  e.g. I cordially dislike (f K {x=3})
> meaning (f (K {x=3})).
>
> My preference is for (3), which allows record selection with
> spaces (which some argue for).  But (2) represents at most a lost
> opportunity, not a bad thing.
>
> Thanks
>
> Simon
>
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