use data-files without installation

[Edward Z. Yang]

Yes, that's possible, though a little difficult to implement portably
(c.f., https://hackage.haskell.org/package/executable-path-0.0.3/docs/System-Environment-Executable.html ).  File a bug, if you like?

Edward

Excerpts from Henning Thielemann's message of 2017-03-03 11:45:55 +0100:
> 
> On Fri, 3 Mar 2017, Edward Z. Yang wrote:
> 
> > One of the tracking bugs we have for this issue:
> > https://github.com/haskell/cabal/issues/4120
> > Note that the data file directory can be overridden
> > with environment variables, that might be good enough to
> > work around.
> >
> > It would be really nice if inplace data files worked.
> > It is a little tricky to do, since the installed layout
> > may not match the inplace layout, but maybe it would be OK
> > if this were just opt in.
> 
> Thank you for the pointer to the ticket. I didn't find it myself because I 
> did not expect that the problem has to do with Nix. :-)
> 
> I see that the problem is hard. Maybe paths relative to the executable 
> could be another option?