cabal design

[Einar Karttunen]

On 16.09 10:02, Isaac Jones wrote:
> The problem I have with --package-db= as a directory for Hugs (and
> nhc, and jhc) is that it conflicts with the meaning of the --prefix
> flag.  That is, if you specify a package database, it changes the
> location of the installation, which is not what you might expect.
> Also, we'd have to make sure people don't try to use --prefix and
> --package-db together in the case of Hugs (unless they're equal).

This could be solved by --ghc-package-db, which would be 
also admitting that it is only a solution for GHC.

For virtualization the solution with JHC will probably be:
1) The virtual root is e.g. /foo/bar
2) export JHCPATH=/foo/bar
3) runhaskell Setup.lhs --prefix=/foo/bar

--package-db would not make much sense.

> > The other proposals (--prefix and --root) require Cabal to magically
> > derive the location of the package database from the "root"
> > directory, but that's magic that we don't need/want IMO.
> 
> So for the sake of those who haven't read the wiki page, here's my
> --root= proposal.  This basically directly implements "virtualization"
> in Cabal:
> 
>     * For GHC
>       o --prefix now becomes $(ROOT)/$(PREFIX)
>       o the ghc-pkg file is stored in $(ROOT)/.whatever
>       o Cabal adds package-conf related flags to ghc and ghc-pkg to
>         look at $(ROOT)/.whatever.
>     * For Hugs
>       o -P$(ROOT)/usr/lib/hugs will be added
>       o Hugs still has issues if --prefix isn't something Hugs knows
>         about (as now). See web page below for comments on how to
>         solve that problem.

This is evil. If given --prefix then the user will want things
to live there. This forces a fixed layout under the throats of users.

This would be mean that my current ${HOME}/local would become 
${HOME}/local/usr/lib/... which is unlike other applications.

> http://www.haskell.org/hawiki/Cabal_2fVirtualizationRequirements

I'll try add comments there.

- Einar Karttunen