Proposal: register a package as providing several API versions
haskell at list.mightyreason.com
Tue Oct 16 08:32:46 EDT 2007
Simon Marlow wrote:
> Several good points have been raised in this thread, and while I might
> not agree with everything, I think we can all agree on the goal: things
> shouldn't break so often.
I have another concrete proposal to avoid things breaking so often. Let us
steal from something that works: shared library versioning on unixy systems.
On Max OS X, I note that I have, in /usr/lib:
> lrwxr-xr-x 1 root wheel 15 Jul 24 2005 libcurl.2.dylib -> libcurl.3.dylib
> lrwxr-xr-x 1 root wheel 15 Jul 24 2005 libcurl.3.0.0.dylib -> libcurl.3.dylib
> -rwxr-xr-x 1 root wheel 201156 Aug 17 17:14 libcurl.3.dylib
> lrwxr-xr-x 1 root wheel 15 Jul 24 2005 libcurl.dylib -> libcurl.3.dylib
The above declaratively expresses that libcurl-3.3.0 provides the version 3 API
and the version 2 API.
This is the capability that should be added to Haskell library packages.
Right now a library can only declare a single version number. So if I update
hsFoo from 2.1.1 to 3.0.0 then I cannot express whether or not the version 3 API
is a superset of (backward compatible with) the version 2 API.
Once it is possible to have cabal register the hsFoo-3.0.0 also as hsFoo-2 it
will be easy to upgrade to hsFoo. No old programs will fail to compile.
Who here knows enough about the ghc-pkg database to say how easy or hard this
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