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(Imported from Trac #699, reported by @dcoutts on 2010-06-05)
In future, ghc --info will report the global package database location. This can be used to check that ghc and ghc-pkg agree on the same one, as a consistency check to make sure the two programs are from the same ghc installation.
Note that getting the location of the global package db from ghc-pkg is a bit hacky at the moment. One has to use ghc-pkg list --global and parse the result. Perhaps we need another ghc feature request for that.