| 1. f @Int -- traditional, invisible forall 2. f Int -- visible forall,
| Int is unambiguous 3. f (type Int) -- visible forall, Int is ambiguous
Perhaps it would help, in the proposal, to make explicit the argument *against* using @ as the herald for all type arguments. I remember that there *is* such an argument, and I found it quite convincing, but I can't remember it now. Maybe it is there somewhere?
Vlad/Richard?
Simon
PS: I am leaving Microsoft at the end of November 2021, at which point simonpj@microsoft.com will cease to work. Use simon.peytonjones@gmail.com instead. (For now, it just forwards to simonpj@microsoft.com.)
| -----Original Message-----
| From: ghc-steering-committee On Behalf Of Eric Seidel
| Sent: 29 October 2021 02:16
| To: ghc-steering-committee@haskell.org
| Subject: Re: [ghc-steering-committee] Proposal #281: Visible "forall"
| in terms; rec: accept
|
| I would still prefer alternative 5 (using @ as the type herald). I
| really dislike that we would now have three ways to specify a type
| argument:
|
| 1. f @Int -- traditional, invisible forall 2. f Int -- visible forall,
| Int is unambiguous 3. f (type Int) -- visible forall, Int is ambiguous
|
| Ideally I would have single syntax for specifying type arguments,
| which was historically (1). I know that many people would like to
| unify the term and type syntaxes, so I'm ok with (2) as well even
| though the T2T algorithm seemed quite involved. But adding (3) really
| feels excessive.
|
| But I believe I'm a small minority in this opinion, so I don't want to
| stand in the way of a very useful feature.
|
| On Wed, Oct 27, 2021, at 09:56, Richard Eisenberg wrote:
| > It has been two weeks. I have heard no argument against this
| proposal,
| > but Simon Marlow (in the springtime) expressed some puzzlement.
| Simon,
| > what are you thinking about this now? With no further response, I
| will
| > accept this proposal on Friday.
| >
| > Others are also very welcome to chime in!
| >
| > Thanks, all!
| > Richard
| >
| >> On Oct 27, 2021, at 5:30 AM, Spiwack, Arnaud
| wrote:
| >>
| >> I think that the proposal makes a great job at listing the issues.
| It's quite transparent about this, I'm not sure what I could add.
| >>
| >> On Wed, Oct 27, 2021 at 11:29 AM Simon Peyton Jones
| wrote:
| >>> I was indeed confused! Apologies.
| >>>
| >>> But my main point remains: enumerating a list of inconvenient side
| effects and corner cases would be a great service.
| >>>
| >>> Simon
| >>>
| >>> PS: I am leaving Microsoft at the end of November 2021, at which
| >>> point simonpj@microsoft.com will cease to work. Use
| >>> simon.peytonjones@gmail.com instead. (For now, it just forwards
| to
| >>> simonpj@microsoft.com.)
| >>>
| >>> | -----Original Message-----
| >>> | From: Vladislav Zavialov (int-index)
| >>> | Sent: 27 October 2021 10:10
| >>> | To: Simon Peyton Jones
| >>> | Cc: Spiwack, Arnaud ; Richard
| Eisenberg
| >>> | ; ghc-steering-committee >> | committee@haskell.org>
| >>> | Subject: Re: [ghc-steering-committee] Proposal #281: Visible
| "forall"
| >>> | in terms; rec: accept
| >>> |
| >>> | Simon, perhaps you're thinking of another proposal that is
| >>> | currently under committee's consideration?
| >>> |
| >>> | Arnaud was commenting on #281, and you seem to be talking about
| #425.
| >>> |
| >>> | - Vlad
| >>> |
| >>> | > On 27 Oct 2021, at 12:05, Simon Peyton Jones via ghc-
| steering-
| >>> | committee wrote:
| >>> | >
| >>> | > There are a lot of inconvenient side effects and corner cases
| >>> | > > Arnaud, could you enumerate them? Even if (as I strongly
| >>> | hope) we accept this proposal, it's good to have a concrete
| list
| >>> | of things to
| >>> | bear in mind. I for one do not have such list in my head.
| >>> | >
| >>> | > One principle that the proposal espouses (but perhaps does
| not
| >>> | call out explicitly) is that it should be possible to write an
| explicit
| >>> | binder for every in-scope variable. So instead of
| >>> | > data T (a :: k -> k) = ... I want to write
| >>> | > data T @k (a :: k -> k) = ... with an explicit
| binder
| >>> | > for k.
| >>> | >
| >>> | > So I see the proposal as removing an ad-hoc wart in the
| language.
| >>> | But I may be blind to the "inconvenient side effects and corner
| cases"
| >>> | and I'd welcome a list of such cases.
| >>> | >
| >>> | > Simon
| >>> | >
| >>> | >
| >>> | > PS: I am leaving Microsoft at the end of November 2021, at
| >>> | which point > simonpj@microsoft.com will cease to work.
| >>> | > Usesimon.peytonjones@gmail.com instead. (For now, it just
| >>> | forwards to > simonpj@microsoft.com.) > > From:
| >>> | ghc-steering-committee >
| >>> | On Behalf Of
| Spiwack,
| >>> | > Arnaud > Sent: 27 October 2021 09:20 > To: Richard Eisenberg
| >>> | > Cc: ghc-steering-committee
| >>> |
| >>> | > Subject: Re: [ghc-steering-committee] Proposal #281: Visible
| >>> | "forall"
| >>> | > in terms; rec: accept
| >>> | >
| >>> | > I've been struggling to have an opinion on this PR. I'm very
| >>> | sympathetic to the goal of the proposal (and this latest
| rendition
| >>> | of the proposal is a really good document). There are a lot of
| >>> | inconvenient side effects and corner cases (but, to be fair,
| these
| >>> | are not special to this proposal: they are inherent to the
| >>> | dependent types plan). But I'm fairly convinced that this is
| the
| >>> | best possible approach, or close enough.
| >>> | >
| >>> | >
| >>> | >
| >>> | > So yes, I don't really feel strongly about it. But on
| balance,
| >>> | I think that I'm in favour.
| >
| > _______________________________________________
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| > ghc-steering-committee@haskell.org
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