On Fri, Sep 25, 2015 at 12:18 PM, Eric Seidel <e...@seidel.io> wrote:
> I've been meaning to ask about this as well. It also forces tools like > ghc-mod and hdevtools to be cabal-aware, which is an unnecessary source > of complexity IMO. > This would certainly be nice, but... GHC certainly has enough information to generate these macros, as it > knows which packages (and versions) it's compiling against. > It knows at some point, but it doesn't necessarily know before parsing the module, at which point it is too late. I can have two versions of a package A, and two other packages B and C that depend on different versions of A, and depending on whether a module M uses package B or package C, M will see different versions of package A automatically. This is all slightly magical, and I have to say I don't entirely understand how GHC decides which versions to expose in general, but that's how GHC works today and it's quite convenient. GHC could provide MIN_VERSION_* macros for packages that have had their versions specified with -package or similar flags (which is how Cabal invokes GHC). That would go only a small way towards the original goals though. (Also, I wonder how MIN_VERSION_* fits into a Backpack world...) Regards, Reid Barton
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