Why is there a cabal file at all?

[Marc Weber]

> Visual Haskell, HackageDB, cabal2rpm, and dh_haskell are all tools
> that read the .cabal file and perform operations based on the package
> metadata.  

In which information are they particularely interested?
Am I right that they the main goal is getting to know which are the
source files and which dependencies to add?

Neil, I begin to see: Its possible to add dependencies
automatically using IDEs to cabal files, but not to haskell files..
Thus if you use liftM an IDE could add
	import Monad
as well as
	build-depends: mtl

Marc