On Thu, 2006-08-10 at 19:31 +0300, Einar Karttunen wrote: > Hello > > There was a discussion about the semantics of the package > dependencies on #haskell. Continuing here for clarity. > > build-depends: foo > 1 && < 3 > vs > build-depends: foo > 1, foo < 3 > > and the same with configuration stuff: > > packages(foo >1 && < 3) > vs > packages(foo > 1) && packages(foo < 3) > > > Current Cabal and the configurations patch interpret these as: > * "packages(foo >1 && < 3)" > * there exists a package foo such that the version is >1 and <3 > > * "packages(foo > 1) && packages(foo < 3)" > * there exists a package foo such that the version is >1 *and* > * there exists a package foo such that the version is <3 > > This means that the semantics are very simple, each package > and depend can be handled in isolation. This has not caused > problems but should be documented more clearly. > > The alternative solution is to make package names have > per-configuration and per-build-depend-line specific scope > and add an environment to the semantics. This would eliminate > a class of errors, but on the other hand make reasoning > about the semantics harder.
Isn't the semantics quite simple: for each package mentioned in build depends, a candidate package must satisfy all constraints. for the current implemented semantics it's: for each dependency there must exist a candidate package that satisfies it. So "build-depends: foo > 1, foo < 3" means linking with foo twice (and possibly different versions)! This seems like nonsense. If that's what it means then it should be an error condition with a helpful message to use "build-depends: foo > 1 && < 3" instead. Similarly if we go with "packages(foo >1 && < 3)" meaning something different from "packages(foo > 1) && packages(foo < 3)" then is the latter not simply an error? Duncan _______________________________________________ cabal-devel mailing list cabal-devel@haskell.org http://www.haskell.org/mailman/listinfo/cabal-devel
