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If by "faulting in" you mean downloading and installing missing dependencies, then that's exactly what the cabal-install tool does.
This is exactly by "faulting in" .. an analogy ... Installing cabal-install seems to be a chicken and egg problem if enough packages are not already installed ... if not enough then one (me) can die of a thousand paper cuts bootstrapping packages up to where cabal-install can be installed. I am running Ubuntu Linux. Cabl-install is written in Haskell? If so, is there a pre-compiled Cabal-install that I can just install with all dependencies (packages) including. I also want to install HaskellDB painlessly ;^) ??
As you mention in your other email, Cabal and cabal-install do indeed access the db of installed packages and build a dependency graph. cabal-install also uses a simple constraint solver to find a satisfactory dep graph of installable packages.
Duncan