[Haskell-cafe] library conflicts and how to resolve them

Andres Löh andres.loeh at googlemail.com
Sun May 6 22:06:14 CEST 2012


> $ cabal install persistent
> Resolving dependencies...
> In order, the following would be installed:
> aeson- (reinstall) changes: mtl-2.1.1 ->
> persistent- (new package)
> cabal: The following packages are likely to be broken by the reinstalls:
> buildwrapper-0.5.2
> Use --force-reinstalls if you want to install anyway.
> Any ideas what is going on ? I believe aeson-  is already installed.


> And as far as I can tell the build of aeson- doesn't require that
> specific version of mtl.

It doesn't, otherwise it couldn't already be installed. Something
persistent depends on in the selected plan depends on mtl-, and
therefore implies the reinstall.

It'd be interesting to see the trace of the solver (pass -v3 to the
cabal command). You could also try what adding --constraint="mtl ==
2.1.1" yields.


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