[ghc-steering-committee] #682: Explicit Level Imports, recommendation: accept

[Moritz Angermann]

Hi all,

I'm generally in support of this proposal. As many of you know, I strongly
believe TemplateHaskell is a major wart that Haskell has, for many
reasons. This proposal tries to address at least one of those: adding more
clarity and explicitness about dependencies. It may help with
cross compilation in that we have a clearer idea of what we exactly need to
load in iserv (alternatives where we implicit link a runnable for
target evaluation, can rely on dead code elimination for this, but having
this from the start would already be helpful).

I've recently been looking a lot at Zig's comptime, as they seem to have
gone down almost the same route. Maybe there's some inspiration to
be drawn from Zig's solution in the future. It is, however, WAY more
restrictive than what we currently have in the form of TemplateHaskell.

+1 on this one.

Best,
 Moritz

On Fri, 10 Jan 2025 at 18:19, Adam Gundry <adam at well-typed.com> wrote:

> Thanks Arnaud! With my "proposal co-author" hat on, I'd like to make a
> few points inline...
>
>
> On 09/01/2025 06:34, Arnaud Spiwack wrote:
>  >
> > On Thu, 9 Jan 2025 at 15:31, Arnaud Spiwack <arnaud.spiwack at tweag.io
> > <mailto:arnaud.spiwack at tweag.io>> wrote:
> >
>  >     [...]
> >
> >     They introduce a new extension-XNoImplicitStagePersistence which
> >     disables that, and a little bit of syntax to specify the stage of
> >     imports. That's it.
> >
> >     But it comes with severe limitations, most importantly: you can't
> >     ever use a symbol defined in the current module in a quote or splice
> >     of this current module, typed template Haskell is turned off.
>
> Regarding typed TH, the proposal currently grants a bit of flexibility
> to the implementation in suggesting that TTH might not be supported at
> all, primarily because TTH has some existing unresolved issues around
> constraints. We could alternately say that TTH remains available (but
> also remains somewhat broken, because fixing it is out of scope of the
> implementation of this proposal).
>
>
> >     For these situations, the proposal kind of advertises using
> >     `-XImplicitStagePersistence`. Which does seem like a fork-like
> >     situation to me. Not cool.
>
> Rather than seeing ImplicitStagePersistence as creating a language fork,
> I see it as necessary for backwards compatibility, but with the
> intention that in the long term NoImplicitStagePersistence is the way to
> go. This may still be difficult in some cases (e.g. codebases that make
> heavy use of Lift), but the idea is to start with a simple, restrictive
> baseline (NoImplicitStagePersistence) and then gradually add features
> relaxing this as needed (ExplicitLevelImports being the first of these,
> but perhaps later something for multiple levels within a single file).
>
> Cheers,
>
> Adam
>
>
> --
> Adam Gundry, Haskell Consultant
> Well-Typed LLP, https://www.well-typed.com/
>
> Registered in England & Wales, OC335890
> 27 Old Gloucester Street, London WC1N 3AX, England
>
> _______________________________________________
> ghc-steering-committee mailing list
> ghc-steering-committee at haskell.org
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-steering-committee/attachments/20250110/808d1b1e/attachment.html>