Bulat Ziganshin wrote:

what about adding to .cabal file ability to ask for specific Cabal version? it will allow to make incompatible changes between Cabal versions. program that uses services specific to Cabal 1.4.x, for example, will just ask for using this Cabal version and operation will go fine

of course, it will require to have cabal 1.4.x, 1.6.x and other versions simultaneously installed - just like now it's possible (in ghc) to have different versions of any other lib installed together

We already have this: the cabal-version field in the .cabal file specifies which version you want, and the cabal-setup program selects the right version. cabal-setup wasn't part of the recent Cabal release, but it's in the repository and will be in the next release (I hope). Cheers, Simon