The error is saying that it can not find `typeOf` in the `Typeable` class. This is because that function is not longer part of the `Typeable` in ghc7.8 and moving forward. Error like this are still be sorted out for ghc 7.8. You are on a bleeding edge version of ghc so packaging problems like this are expected. Package stability is usually marked by when the Haskell Platform updates to the new ghc version.
So if you want additional stability HP is where it is at. If you want to live and the bleeding edge then you can download sdl with cabal unpack and see if you can not fix the problem for yourself.
Here is a link to the `Typeable` module in base:
There is replacement function for backward compatibility.
http://hackage.haskell.org/package/base-4.7.0.0/docs/Data-Typeable.html#v:typeOf
If you fixed the import statement for all of the sdl modules, you might fix the incompatibility with the new Typeable. There will probably be a few other issues that need solving after this one. I have updated several packages on a case by case basis when I need them to new ghc version and has been a lesson in understanding ghc errors and fixing them. If you have the time I recommend giving it a shot.
Patrick