On Sun, 2010-04-11 at 14:28 -0700, Jason Dagit wrote:

> I've noticed another type of diamond dependency problem.  Suppose I
> build and install Foo today and it depends on Bar 2.0.0.  In a week, I
> install Bar 2.0.1.  Next I installed Baz that also depends on Bar, and
> it gets Bar 2.0.1.  When I install a package that depends on Foo, Baz,
> and possibly Bar, then cabal won't be able to figure out proper
> dependencies because Foo needs one version of Bar and Baz needs a
> different version.

That's exactly the problem that cabal-install solves. It will rebuild
one or the other of Foo and Baz so that the dependency on Bar is
consistent.