#925: More flexible constraints, specified via local preferences file ---------------------------------+------------------------------------------ Reporter: snoyberg | Owner: Type: enhancement | Status: new Priority: normal | Milestone: cabal-install-0.14 Component: cabal-install tool | Version: 1.10.2.0 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Changes (by kosmikus): * type: defect => enhancement * milestone: => cabal-install-0.14 Comment: I've changed your bug into an enhancement request. What you're describing is intended behaviour. A constraint passed on the command line acts the same as a constraint put in the build-depends of a package, i.e., it not only restricts the range of versions, but also causes the package to actually be installed. The closest to what you want that currently exists is --preference, and it should actually be sufficient in most cases. A --preference constraint does not prevent excluded versions from selected at all, but it will first try all preferred versions. I appreciate the attempt you make with cabal-nirvana, but I don't like that it works by actually changing the downloaded files. Cabal already supports a global preferences file that's downloaded from Hackage. It should probably support local files with preferences, too. That would be relatively easy to change. So there are two possible enhancements in this issue: * introduce a way to easily specify a large number of local preferences, * next to constraints introduced by --preference and --constraint The mail http://www.mail-archive.com/haskell-cafe@haskell.org/msg96962.html as well as the surrounding thread are also somewhat related. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/925#comment:2 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects