Reinstallable - base

[Howard B. Golden]

My _very_ naive question is whether Template Haskell should have all the features of the latest language? Perhaps it could instead be limited to a simpler subset so that it could become a bolt-on to the rest of the compiler and it could be compiled and implemented independently using an older compiler and libraries. 

Howard

> On Oct 17, 2023, at 9:54 AM, Viktor Dukhovni <ietf-dane at dukhovni.org> wrote:
> 
> On Tue, Oct 17, 2023 at 04:54:41PM +0100, Adam Gundry wrote:
> 
>> 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.
> 
> To avoid that problem, GHC's own dependency on "base" could be indirect
> via a shared object with versioned symbol names and a version-specific
> SONAME (possibly even a private to GHC SONAME and private symbol version
> names).  Say "libbase.so.4.19.1".
> 
> The dependency on "base" in the TemplatHaskell generated code would then
> also need to be dynamic, allowing the two versions of base to coexist
> without conflict, both in turn depdent on a common version of the GHC
> internal libraries.
> 
> This would of course somewhat complicate binary distributions, but that
> should be manageable.  Perhaps there are less invasive (more clever)
> solutions?
> 
> -- 
>    Viktor
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