Cabal and simultaneous installations of the same package

Simon Peyton Jones simonpj at
Mon Mar 23 08:45:48 UTC 2015

Dear Cabal developers

You'll probably have seen the thread about the Haskell Platform.

Among other things, this point arose:

|  Another thing we should fix is the (now false) impression that HP gets in
|  the way of installing other packages and versions due to cabal hell.

People mean different things by "cabal hell", but the inability to 
	simultaneously install multiple versions of the same package,
	compiled against different dependencies
is certainly one of them, and I think it is the one that Yitzchak is referring to here.

But some time now GHC has allowed multiple versions of the same package (compiled against different dependencies) to be installed simultaneously.  So all we need to do is to fix Cabal to allow it too, and thereby kill of a huge class of cabal-hell problems at one blow.

But time has passed and it hasn't happened. Is this because I'm misunderstanding?  Or because it is harder than I think?  Or because there are much bigger problems?  Or because there is insufficient effort available?  Or what?

Unless I'm way off beam, this "multiple installations of the same package" thing has been a huge pain forever, and the solution is within our grasp.  What's stopping us grasping it?


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