Lucid Lynx was announced in 2009, and at there time there was no Haskell Platform in Debian to adopt. More recent Ubuntu versions support the HP, however.
Use this [1] to install and maintain various ghc/platform pairs on older versions of Ubuntu. It uses Debian's update-alternatives tool to install multiple versions side-by-side and manage which version is 'active'.
Also, you'll probably need to make sure you've got all the required libraries and their versions [2], 10.04 may need some of them upgraded, not sure.
If that doesn't work, if you have dependency issues and can't fix them, then I suggest installing Ubuntu Server 12.04 in a virtual machine and playing with Haskell there instead. Ubuntu Server is relatively small, a base install in a VM is only about 1.5GB.
In the case of Ubuntu, they're just downstream consumers of the Debian Haskell packaging team's efforts, and as a result are sometimes out of sync, http://packages.debian.org/search?keywords=haskell-platform
Lucid Lynx was announced in 2009, and at there time there was no Haskell Platform in Debian to adopt. More recent Ubuntu versions support the HP, however.