[arch-haskell] PKGBUILDs for multiple coexisting versions of GHC

[Rudy Matela]

Hello Arch Haskell,

I am happy to announce PKGBUILDs for legacy versions of GHC that can coexist in
the same install.  This includes coexisting with the current GHC provided by
the arch-haskell repo.  These PKGBUILDs are available on AUR.
https://aur.archlinux.org/packages/?K=ghc
https://aur.archlinux.org/packages/ghc7.8-bin/
https://aur.archlinux.org/packages/ghc7.8/
https://aur.archlinux.org/packages/ghc7.6-bin/
https://aur.archlinux.org/packages/ghc7.6/
(They were silently put on AUR months ago, but I have not announced anywhere.)

For example, on my arch install, I have 5 different versions of ghc:

$ pacman -Qs ghc
local/ghc 8.0.1-1
local/ghc7.4 7.4.2-2
local/ghc7.6 7.6.3-3
local/ghc7.8 7.8.4-1
local/ghc7.10 7.10.3-1

This works by having binaries and relevant files with suffixes:

$ pacman -Ql ghc7.6 | grep /usr/bin
ghc7.6 /usr/bin/
ghc7.6 /usr/bin/ghc-7.6
ghc7.6 /usr/bin/ghc-pkg-7.6
ghc7.6 /usr/bin/ghci-7.6
...

For example, just do `ghc7.6 file.hs` to compile a file with ghc-7.6.3.
Useful for testing libraries for compatibility with older versions of GHC.

All legacy versions have a binary PKGBUILD (-bin) and a source PKGBUILD, the
earlier can be used to compile the latter.


Ideally, I think those packages could be available on a standalone repository
(arch-haskell-legacy or something like that).  Or even as part of the main
arch-haskell repo.  Unfortunately, I do not have the server resources needed
for that: each version takes about 1.5 hours to compile, the resulting packages
would also consume some bandwidth when downloaded.

If anyone is interested in setting up such a repository (Magnus?) -- feel free
to use the PKGBUILDs I provided on AUR.  Also, I will be happy to help with any
scripting necessary to set this up.

Btw, many thanks to Magnus Therning for providing the arch-haskell repository.
It has saved me hours since I started using it.

Regards,
Rudy