When you wrote "or add it to ArchHaskell" I though "oh, really? can I do that?"
So I tried.
First step was to install cabal2arch from [Haskell], then I did "cabal update && cabal fetch download" and extracted the tar.gz.
I ran cabal2arch on the .cabal file, this produced a PKGBUILD and .install files.
Next, I tried makepkg -s and there I got stuck.
haskell-download (trying to build it) depends on haskell-xml (from [Haskell]) which defends on haskell-text (from extra). When trying to install haskell-text from extra I get:
warning: cannot resolve "haskell-deepseq=1.1.0.2-2.1", a dependency of "haskell-text"
Did I do anything wrong? Is it a bug? Should I try installing later?