module Main where import Distribution.Simple72 main = mainWithHooks ( .... ) Could be one way to achieve this goal in most simpler API changes (up to rewriting the whole core using more monads as all information is pased) How could it work? The Cabal distribution ships with src/Distribution/Simple1.hs: import Distribution.Simple2 import Types1 import Types2 -- wrapper for the new Simple2 api exporting API1 [..] src/Distribution/Simple2.hs: import Distribution.Simple3 [..] I guess you get the idea. This way API v1 uses API v2 using API v3 .. using API vlatest. There is another case: What happens if the Setup.hs fits a newer cabal version (2) but you have only (1) installed? You could get an api wrapper mapping API v2 back to API1 you have. And the cool thing: Adding this wrapper could be automated because reading the Distribution.SimpleX versions is simple.. Propably the best way handling this case is: Update your Cabal version anyway :) It's a nice documentation about how to upgrade your Setup files as well.. because looking at the "dummy" files only calling the other API versions should give you all you need. I'm not sure about how everyone would like having Distribution/Simple{1,2,3,4,5,6,7,8,9,...200}.hs files But thinking about how many cabal using people could benefit from this easy to accomplish up and downgrading it might be worth it. Some small changes (removing the Bool arg in runTests) and the flagVerbose change would be really trivial then without having to read lots of Cabal code I think Cabal devs know best how often this could have helped people ? It would make the life of all package mantainers a lot easier.. and of those devs having SetupX{1,2,3}.hs flying around. You can't forget about all trouble.. just about some incompatibilies. Any thoughts? Marc Weber