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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