How can I install haskell-platform?

This bug has now been fixed and is in 11.04 -proposed. Therefor you can enable proposed packages and install haskell-platform. If you do not want to keep getting -proposed updates you can disable it once you have haskell-platform installed. Look here for a guide on how to enable -proposed updates.

This bug is fixed in 11.10.

I am afraid you are out of options for the moment besides compiling it yourself (but editing the package seems alot less problematic).

Either you edit var/cache/apt/pkgcache.bin as shown at comment #12 in the bug or you will have to wait until all the problems have been ironed out for using the Haskell platform on Ubuntu 11.04

I would go with editing the package. It is not that difficult and I expect you to be able to do that without any problem.

edit: now I am on my own machine.

cd /var/cache/apt/
sudo cp pkgcache.bin pkgcache.backup.bin
sudo cp pkgcache.bin pkgcache.test.bin
sudo vi pkgcache.test.bin

enter

/6.12.1+

This will result in:

009fe21547b0cc8fc2f7ee1ec74d3e27^@haskell-http-doc^@1:2^@libghc6-http-
doc^@^@009fe21547b0cc8fc2f7ee1ec74d3e27^@2.7.0-
2^@xemacs22^@^@b8b7ecd2f37fbc271d0108a704c42056^@haskell-pcre-light-doc^@1:2^@libghc6-
pcre-light-doc^@^@009fe21547b0cc8fc2f7ee1ec74d3e27^@haskell-
platform^@2010.1.0.0.1^@6.12.1^@6.12.1+^@libghc6-cgi-dev^

See the 6.12.1 at the bottom?

Navigate with the arrow keys to the 1 of .1+ When on the 1 hit r 4 :wq!

That's the practise run. Remove the .test from the sudo vi pkgcache.test.bin to change the real file. After that install it in the normal way.