[ghc-steering-committee] Record syntax

[Joachim Breitner]

I know I know. It matters for what are the names of variables. My mental parser first looks what are the names (and handles module prefixes), and then the expression parser runs. At least in my head.

And module prefixes are not arbitrary expressions (yet…), but the `r` can be an arbitrary complex expression!

   f (foo bar // baz).r

vs

   f (foo bar // baz) .r

would be different under your proposal, but the same under mine.

But none of this is new to anyone here… why not just vote and get a decision?

Cheers,
Joachim


Am 28. Januar 2020 12:58:34 MEZ schrieb Simon Peyton Jones <simonpj at microsoft.com>:
>|  With function application, no space or space is irrelevant:
>|  
>|    f r"" = f r "" ≠ f (r "") = f (r "")
>
>But that is not so
>
>	f r x  ≠   f rx
>	f M.x  ≠   f M x
>
>White space (or its absence) matters.
>
>Simon
>
>|  -----Original Message-----
>|  From: ghc-steering-committee
><ghc-steering-committee-bounces at haskell.org>
>|  On Behalf Of Joachim Breitner
>|  Sent: 28 January 2020 11:55
>|  To: ghc-steering-committee at haskell.org
>|  Subject: Re: [ghc-steering-committee] Record syntax
>|  
>|  Hi,
>|  
>|  > Consider  (f .x g .y h .z)
>|  >
>|  > (2) says this means ((((f .x) g) .y) h) .z), so that it
>parenthesises
>|  > exactly like function application.
>|  >
>|  > (3) says it means (((f .x) (g .y)) (h .z)) which, while
>unambiguous,
>|  > I dislike cordially.
>|  >
>|  > I propose to adopt (2).
>|  
>|  I agree that “exactly like function application” is a great, simple
>|  universal way of explaining the parsing.
>|  
>|  But I can't stop pointing out that this is inconsistent if we insist
>|  that `f r.x = f (r.x)`.
>|  
>|  With function application, no space or space is irrelevant:
>|  
>|    f r"" = f r "" ≠ f (r "") = f (r "")
>|  
>|  You propose
>|  
>|    f r.x ≠ f r .x = f (r .x) = f (r .x)
>|  
>|  while I am still attached to
>|  
>|    f r.x = f r .x ≠ f (r .x) = f (r .x)
>|  
>|  I know that this will disappoint a few who want their code to look
>like
>|  it does in some other languages (many object oriented langauges,
>|  Ocaml), and who do not want to put in the extra parentheses. But in
>|  this case I am leaning towards the elegance of _really_ saying
>“exactly
>|  like function application”, not only syntactically, but also morally
>(a
>|  record is a function on a finite set of field names.)
>|  I find this very justifiable for a functional programming language.
>|  
>|  And I find it very un-haskelly that going from a space to no space
>|  between expressions makes a difference (I believe Simon Marlow
>shared
>|  this reservation.)
>|  
>|  
>|  If we do insist on “binds more tightly if no space”, then I am
>actually
>|  in favor of “also binds more tightly if there is a space”, i.e. (3)
>|  above, to avoid the whitespace-sensitivity.
>|  
>|  
>|  So if it comes to a vote, I think these three options cover all
>|  opinions so far?
>|  
>|   * f r .x = (f r).x; f r.x = f (r.x)     -- Simon’s (2)
>|   * f r .x = (f r).x; f r.x = (f r).x)    -- My take on it
>|   * f r .x = f (r.x); f r.x = f (r.x)     -- Simon’s (3)
>|  
>|  Anything else?
>|  
>|  
>|  If we vote, I hope we don't get too many abstinations. Nobody will
>be
>|  personally offended if you vote “against” them (I hope), but
>whatever
>|  outcome we have better have weight, and is supported by a high
>turnout.
>|  
>|  
>|  And I think we should just vote; we keep rephrasing the same
>arguments
>|  with different words.
>|  
>|  Cheers,
>|  Joachim
>|  
>|  --
>|  Joachim Breitner
>|    mail at joachim-breitner.de
>|  
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