On Thu, Apr 8, 2010 at 11:00 AM, Sean Leather <leather@cs.uu.nl> wrote:
> I created a few tools to help me manage multiple GHC distributions in a Bash
> shell environment. Perhaps it's useful to others.
>
> http://github.com/spl/multi-ghc
>
> Feedback welcome. I'd also like to know if something similar exists.

Does this also work with a system installed ghc? These are usually
installed in /usr (I'm using Gentoo Linux):

$ ls -l /usr/bin/ghc*
lrwxrwxrwx 1 root root 10 dec 22 00:22 /usr/bin/ghc -> ghc-6.12.1
-rwxr-xr-x 1 root root 279 dec 22 00:20 /usr/bin/ghc-6.12.1
lrwxrwxrwx 1 root root 11 dec 22 00:22 /usr/bin/ghci -> ghci-6.12.1
-rwxr-xr-x 1 root root 61 dec 22 00:20 /usr/bin/ghci-6.12.1
lrwxrwxrwx 1 root root 14 dec 22 00:22 /usr/bin/ghc-pkg -> ghc-pkg-6.12.1
-rwxr-xr-x 1 root root 262 dec 22 00:20 /usr/bin/ghc-pkg-6.12.1

The ghc-config Bash script in multi-ghc uses symlinks to determine which is the "current" version to use. The instructions on the GitHub page explain it in detail, but here's how my setup works.

* I create /opt/ghc for storing GHC, clone the multi-ghc repository (or copy the files) here.
* I create /opt/ghc/6.10.4/src, download http://www.haskell.org/ghc/dist/6.10.4/ghc-6.10.4-i386-unknown-linux-n.tar.bz2 , and untar it here.
* cd ..; ln -s ../Makefile; make install

ghc-config creates a $HOME/.ghc-config directory for tracking the current version and symlinks. Now, the key for your situation (I think) is your $PATH. If you append $HOME/.ghc-config/ghc/bin to your $PATH after /usr/bin, then you can use ghc-6.10.4 to call this specific version.

Unfortunately, there is still a problem. ghc-config also manages $HOME/.cabal as a symlink for the current version. So, that would most likely conflict with your setup. There may be a way to fix that, though I haven't looked into it, or I could separate the cabal configuration from the ghc configuration.

If so, I think I'm going to use this tools since I occasionally like
to try out ghc-HEAD.

multi-ghc should also work for doing this. As long as you install it as /opt/ghc/6.13.blah (or whichever directory you want to use instead of /opt/ghc). This was one of the goals of the design.

There's more documentation in the README.md and scripts. I'm happy to improve upon it if something doesn't work.

Sean