[Haskell-cafe] Cabal: wrapping namespace of a package into top-level module

[Brandon Moore]

----- Original Message -----

> From: max ulidtko <ulidtko at gmail.com>
> To: haskell-cafe at haskell.org
> Cc: 
> Sent: Monday, May 23, 2011 11:38 PM
> Subject: [Haskell-cafe] Cabal: wrapping namespace of a package into top-level module
> 
> Hi haskell-cafe.
> 
> I have a package which builds with cabal pretty fine, but there is
> namespace issue which disturbs me. The problem is that the package
> exports (to the toplevel namespace!) some modules with fairly general
> names, like Tests, Basics, Applications. This is probably an oversight
> of the original package author, and the namespace shouldn't be organised
> like this... but it is. And I'm looking for a way to avoid potential
> namespace troubles should I install the package, other than going and
> reforming the namespace tree myself.


Whatever you do, you should mail the package author suggesting
a better organization (including a patch, if you do reorganize the module
yourself).


I think there are three options with current tools

1) If you don't actually want to make modules with those names,
it might not be a problem for now.

Just like you don't get errors from importing multiple modules with conflicting
identifiers unless you actually use the identifiers, there shouldn't be errors
if you happen to use two packages defining a module with the same name,
unless you actually try to import that module.

2) If you do want to reorganize the package, I think a textual replace changing the
old fully-qualified names to the new should work. Here are some suggestions
for automating it with various little unix tools, but I haven't tried on a nontrivial package.

mkdir -p New/Prefix/
mv $SOURCEDIRS New/Prefix/
sed -n '/exposed-modules/,/:/p' $PKG.cabal | grep -v : | tr -d '[[:blank:]]' > modules
awk '{print ",s/"$0"/New.Prefix."$0"/g"} END {print "wq"}' > rename.ed
find . -name '*.hs' -exec ed {} < rename.ed \;

If you decide to write your program against the current names while waiting for the
author to change them, the same sort of thing should work for updating module
names in your program.

3) There's also package-qualified imports, but I don't think you should use them -
if there are actually conflicts on those top-level module names, the package
should be fixed sooner rather than later.


www.haskell.org/ghc/docs/7.0.3/html/users_guide/syntax-extns.html#package-imports


> What I was thinking about was some cabal option to "wrap" 
> package's
> namespace into a toplevel module, say "PackageName", so that module
> Tests could be imported by usual code with `import PackageName.Tests`.
> Is that possible with cabal?
>
> Things are further complicated by the numerous intra-library imports.
> While the "outside" code refers to a module with 
> PackageName.ModuleName,
> it would be very desirable that "inside" code used just straight
> ModuleName.

It's been discussed before, but not implemented

http://hackage.haskell.org/trac/ghc/wiki/Commentary/Packages/PackageMountingProposal


Brandon