Help understanding a dependency conflict

[Henning Thielemann]

On Fri, 7 Jan 2011, tsuraan wrote:

> I have a program that's using both json (0.4.4) and hslogger (1.1.0).
> During the "cabal configure" stage of compiling my program, I get this
> error message:
>
> Warning: This package indirectly depends on multiple versions of the same
> package. This is highly likely to cause a compile failure.
> package json-0.4.4 requires mtl-1.1.0.2
> package hslogger-1.1.0 requires mtl-2.0.1.0
>
> Looking at the .cabal files for json and hslogger, they both have
> dependencies on "mtl", but neither package gives a version for it.  I
> only have mtl 2.0.1.0 installed, so installing json didn't bring in an
> old version of the library when it was installed.  My program compiles
> and runs without any errors.  Can anybody tell my why cabal thinks
> json needs mtl 1.1.0.2, and what I can do to make the message go away?

Does any of the packages, that json and hslogger depend on, has more 
restricted version dependencies?