A 30/10/2012, às 09:33, Chaddaï Fouché escreveu:
There is some good explanations of that phenomenon around under the name "Butterfly effect" like : http://cdsmith.wordpress.com/2011/01/17/the-butterfly-effect-in-cabal/
This is really painful when you start to have accumulated a number of packages, and the more dependencies, the more likely you are to hit this... Which is why most people now recommend using sandboxes for installations, to allows you to have several different packages database and not have to scratch your whole GHC installation once you've damaged it (there are always alternative to this radical step, but it takes more time than restarting from zero so nobody use them). Basically, as soon as you hit a problem with a cabal installation that would require a reinstall, you restart from a new sandbox. The solutions to do that are virthualenv, capri or cabal-dev and the next release of cabal itself should have a sandbox mode.
The proper solution would be to allow several version of the same package version to cohabit but that's pretty complicated and not yet possible.
After reading that post and a couple others I tried to install cabal-dev which is supposed to help with some of these issues. Ironically it doesn’t install either... miguelnegrao@Mac-Miguel:~$ cabal install cabal-dev Resolving dependencies... [1 of 1] Compiling Main ( /var/folders/ps/fvzyp6yj5k743k1clpmt24kw0000gn/T/cabal-dev-0.9.1-11243/cabal-dev-0.9.1/Setup.hs, /var/folders/ps/fvzyp6yj5k743k1clpmt24kw0000gn/T/cabal-dev-0.9.1-11243/cabal-dev-0.9.1/dist/setup/Main.o ) Linking /var/folders/ps/fvzyp6yj5k743k1clpmt24kw0000gn/T/cabal-dev-0.9.1-11243/cabal-dev-0.9.1/dist/setup/setup ... ld: warning: could not create compact unwind for _ffi_call_unix64: does not use RBP or RSP based frame unrecognized option `--disable-benchmarks' Failed to install cabal-dev-0.9.1 cabal: Error: some packages failed to install: cabal-dev-0.9.1 failed during the configure step. The exception was: ExitFailure 1 miguelnegrao@Mac-Miguel:~$ cabal -V cabal-install version 1.16.0.1 using version 1.16.0.2 of the Cabal library Is this a lost cause ? :-) best, Miguel