Help understanding a dependency conflict

[tsuraan]

> Is there a reason you need to make the warning go away?

I'm a haskell newbie, and the build system is telling me I'm doing
something that may break my program.  I'd definitely be happier if the
warning weren't there :)

> Maybe your installed version of parsec is built against mtl-1 - parsec
> is a dependency of json.

ghc-pkg doesn't list mtl as a dependency of parsec.  I didn't think I
had mtl-1 installed (it's not in my .cabal directory), but now I see
that it's part of the haskell base install.  So now I'm wondering why
cabal felt that it needed to install mtl-2 for hslogger, when I
apparently already had mtl-1 installed, and hslogger doesn't list a
version for its mtl dep.  Is it because hslogger depends on base >= 4,
while json depends on base >= 3?  Does that sound like a probable
cause?