Does any of the packages, that json and hslogger depend on, has more restricted version dependencies?
From looking at the json.cabal file and assuming default build settings (I didn't touch them, anyhow), json depends on base, syb, array, containers, bytestring, mtl, parsec, and pretty. My ~/.cabal/lib only has an entry for mtl, so I assume the rest of the packages are build-in to haskell and are probably not dependent on mtl.
From the hslogger.cabal file, hslogger depends on network, mtl, unix, base, containers, directory, process, time, and old-locale. Of those, only mtl is on my ~/.cabal/lib file, so I assume again that nothing else depends on mtl.
Is there some way to have cabal (or some other ghc packaging program) tell me about dependencies, and what packages have brought in what other packages? I can't imagine that digging through .cabal files is the normal way to figure this out.