copy / register / --gen-script and --destdir

[Marc Weber]

> The --destdir is like automake's "make install DESTDIR=$TMP/blah"
> feature. But using configure --prefix should change what register
> --gen-script produces, so if that's not happening then it's a bug I
> think.

Perhaps I should tell you what I am about to do.
I want to register some cabal packages in the nix software distribution
system.
a -> b   Package a depends on b and c
  ` c

Right now when a is build nix does create a new package databse
registering b and c.

I think this can be done better by letting b and c have its own package
database containing only their libs of their own.

Then when a has to be build 
GHC_PACKAGE_DATABASE=<path to pkg-db a>:<path to pkg-db b> 
can be used to tell ghc where to find those libs.

Thus my trouble is that I should copy the lib to
/nix/store/<somepath>/

Currently I'm using sed to prefix the right prefix using --gen-script ..

Fixing cabal (if there is something to fix) does'nt have high priority
for me right now.

And in the long run I think we should think about writing something
similar to scons (python build system) because some features should be
written anyway (such as module dependency tracking ... )
At the moment I'm not sure how this should look like in detail.

Thanks
Marc