Just get 13.10, I think Haskell platform missed the Ubuntu 12 release and it causes major pain.
apt-get install haskell-platform
cabal update
cabal install cabal-install # gets 1.18v
Add this line to the bottom of .profile
PATH="$HOME/.cabal/bin:$PATH"
Check cabal --version
Done.
Can I install the 13.10 package onto 12.04? Or do you mean upgrading from Ubuntu 12.04 LTS to 13.10? I've thought about that. Just makes me nervous.

I let the build run all night but there's an error in the html file it can't get past. I change the build file to not build the docs, and have restarted the compile. Sadly it's back on stage 0 but I'm letting it run all day while I'm at work.
I did try updating cabal before but didn't use "cabal install cabal-install". Maybe that will upgrade me. I wasn't able to directly upgrade base to 4.6.0.1 from within cabal that I could tell, and my base version was to old for your dependencies it seemed.
Edit: Perhaps I'm not meant to be a part of this project, lol.
[73 of 73] Compiling Main ( Main.hs, dist/build/cabal/cabal-tmp/Main.o )
Linking dist/build/cabal/cabal ...
Installing executable(s) in /home/ubuntu/.cabal/bin
ubuntu@ip-10-143-203-223:~/code/proxypool$ cabal --version
cabal-install version 0.14.0
using version 1.14.0 of the Cabal library
But wait! ~/.cabal/bin you say?
ubuntu@ip-10-143-203-223:~/code/proxypool$ ~/.cabal/bin/cabal --version
cabal-install version 1.18.0.2
using version 1.18.1.2 of the Cabal library
But alas, even with cabal 1.18 I'm still stuck with base-4.5.0.0 which fails the base ==4.6.* check.