[ghc-steering-committee] Records again

[Simon Peyton Jones]

| I.e. I will support `f r.x = f (r.x)`, if I can still add space before the
| .x.

That gets into a separate question, the "naked selector" question.  There we have the following viable alternatives

(1) .x is illegal
(2) .x means (\r. r.x)
(3) .x is a postfix operator

Certainly (3) would all you to write
	r .x .y        meaning r.x.y
or
	f (r .x .y)    meaning f (r.x.y)

But I was trying to close the discussion of (f r.x) before opening the discussion about 1/2/3 for naked selectors.

Simon

-----Original Message-----
| From: ghc-steering-committee <ghc-steering-committee-bounces at haskell.org>
| On Behalf Of Joachim Breitner
| Sent: 17 December 2019 10:33
| To: ghc-steering-committee at haskell.org
| Subject: Re: [ghc-steering-committee] Records again
| 
| Hi,
| 
| Eric nicely summarizes my thoughts
| 
| I am a happy user of
| 
|   f r.x .y = f (r.x.y)
| 
| in Ocaml, and I agree that it is not an absolutely horrible choice, and
| will likely vote it over Reject.
| 
| 
| I would find it bad, though, if we have
| 
|   f r.x.y = f (r.x.y)
| 
| but disallow or give completely different meaning (as in the bare .y
| variants) to
| 
|   f r.x .y
| 
| (where the space could still be a newline). Record accessors can possibly
| be deeply nested, so it should be possible to nicely wrap or vertically
| align the code. This indicates that postfix .x should parse similar to
| postfix `{x=1}` (what a nice coincidence that both relate to records).
| 
| So while I fully understand the analogy to module qualifiers, this aspect
| already makes them different.
| 
| 
| In the end I am a big fan of the fundamental rule of mentally parsing
| Haskell code, namely “function composition binds most tightly and
| associates to the left”.
| Yes, there are exceptions (qualified names, record updates).
| And yes, variant “JS” and “JS+Section” are still a slight exception to that
| rule (as there record accessors associate with function application).
| 
| So maybe my current thinking is
| 
|  JS+Section > JS > Ocaml+Section > Ocaml > SectionSelector
|     > Reject > OnlySelection > PlainSelector
| 
| 
| I.e. I will support `f r.x = f (r.x)`, if I can still add space before the
| .x.
| 
| I am not yet completely decided what to think of disallowing `f r .x`.
| 
| 
| 
| Oh, and here is a nice way to justify the JS variants functionally. Not
| sure if it is helpful… A record r with fields foo and bar can be thought of
| as a _function_ with domain {.foo, .bar}. In that point of view,  the
| syntax
|    f .foo
| 
| 
| 
| 
| Cheers,
| Joachim
| --
| Joachim Breitner
|   mail at joachim-breitner.de
|   http://www.joachim-breitner.de/
| 
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