I think it is making progress. It's not just an engineering milestone
but also messaging. Right now a huge issue that every Haskeller faces is
new GHCs having new major versions of base. If we make clear that "it's
not base's fault, it's Template Haskell's fault", then we will have an
easier time coordinating people and eventually fundraising to get issued
fixed with Template Haskell.
John
On 10/20/23 03:56, Arnaud Spiwack wrote:
A very large proportion of libraries, and virtually all end-user
applications, transitively depend on Template Haskell. Whether they
use Template Haskell directly or not. So if we're saying “base is
reinstallable, except when you have Template Haskell somewhere”, we're
effectively saying “base is not reinstallable”. Now, it could be a
good stepping-stone, from an engineering standpoint, but I don't think
we could deliver this and be satisfied that we've accomplished anything.
On Thu, 19 Oct 2023 at 13:47, Oleg Grenrus <oleg.gren...@iki.fi> wrote:
For what it worth, `template-haskell` itself depends on a `base`.
So if
`base` if different base is used, different `template-haskell` is
to be
used.
In my opinion is not *too unfair* to require that if you actually
splice
in (i.e. the code not only provides template-haskell combinators to
create/modify splices) then you must have base and template-haskell
versions aligned with host GHC used versions.
The same restriction is GHC plugins, isn't it, except
`template-haskell`
is replaced with `ghc`?
- Oleg
On 17.10.2023 18.54, Adam Gundry wrote:
> Hi Simon,
>
> Thanks for starting this discussion, it would be good to see
progress
> in this direction. As it happens I was discussing this question
with
> Ben and Matt over dinner last night, and unfortunately they
explained
> to me that it is more difficult than I naively hoped, even once
> wired-in and known-key things are moved to ghc-internal.
>
> The difficulty is that, as a normal Haskell library, ghc itself
will
> be compiled against a particular version of base. Then when
Template
> Haskell is used (with the internal interpreter), code will be
> dynamically loaded into a process that already has symbols for
ghc's
> version of base, which means it is not safe for the code to
depend on
> a different version of base. This is rather like the situation
with TH
> and cross-compilers.
>
> Adam
>
>
>
> On 17/10/2023 11:08, Simon Peyton Jones wrote:
>> Dear GHC devs
>>
>> Given the now-agreed split between ghc-internal and base
>> <https://github.com/haskellfoundation/tech-proposals/pull/51>,
what
>> stands in the way of a "reinstallable base"?
>>
>> Specifically, suppose that
>>
>> * GHC 9.8 comes out with base-4.9
>> * The CLC decides to make some change to `base`, so we get
base-4.10
>> * Then GHC 9.10 comes out with base-4.10
>>
>> I think we'd all like it if someone could use GHC 9.10 to
compile a
>> library L that depends on base-4.9 and either L doesn't work at
all
>> with base-4.10, or L's dependency bounds have not yet been
adjusted
>> to allow base-4.10.
>>
>> We'd like to have a version of `base`, say `base-4.9.1` that
has the
>> exact same API as `base-4.9` but works with GHC 9.10.
>>
>> Today, GHC 9.10 comes with a specific version of base, /and you
can't
>> change it/. The original reason for that was, I recall, that GHC
>> knows the precise place where (say) the type Int is declared, and
>> it'll get very confused if that data type definition moves around.
>>
>> But now we have `ghc-internal`, all these "things that GHC
magically
>> knows" are in `ghc-internal`, not `base`.
>>
>> *Hence my question: what (now) stops us making `base` behave
like any
>> other library*? That would be a big step forward, because it
would
>> mean that a newer GHC could compile old libraries against their
old
>> dependencies.
>>
>> (Some changes would still be difficult. If, for example, we
removed
>> Monad and replaced it with classes Mo1 and Mo2, it might be
hard to
>> simulate the old `base` with a shim. But getting 99% of the way
>> there would still be fantastic.)
>>
>> Simon
>
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Arnaud Spiwack
Director, Research at https://moduscreate.com and https://tweag.io.
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