Question

I’m working on the wxHaskell library, and wishing to keep my development work separate from the stable wxHaskell from hackage I’m using cabal-dev in the following manner:

1. I obtained the source for wxHaskell from darcs;
2. Because wxHaskell is comprised of three components I used cabal-dev add-source to add each one (wx, wxcore, wxdirect);
3. I was then able to install into a sandbox local package library by doing cabal-dev install wx, as expected, the dependencies were detected and everything built and installed.
4. Finally I successfully ran my test code by using ghc -package-conf to specify the location of the sandboxed package database.

The problem comes when I make modifications to the wxHaskell source. In order to build and install the updated code I have to use cabal-dev install --reinstall, which makes sense as I don’t increment the version number; the build takes place and I see “Installing library in…” and “Registering…” but the changes I’ve made in the code aren’t present in the recompiled sandbox library.

The work around I have at the moment is to delete the cabal-dev library and repeat the process every time I want to rebuild.

Answer 1

UPDATE: cabal-install >= 1.18 has support for sandboxes, and will be better maintained than cabal-dev going forward. Cabal-install also has better support for using add-source with sandboxes. Here’s a description of the new sandboxing features in cabal-install: http://coldwa.st/e/blog/2013-07-30-Cabal-sandbox.html

Old answer:

As you found, ‘add-source’ is not meant for use with actively changing projects. I’m not sure that there is a good solution there either – it’s difficult to track the location of an add-source’d project (there is no existing infrastructure for that, at least), and I’m not sure that’s always the right thing.

Another workflow may serve you better – just use cabal-dev install, pointing to the sandbox you wish to use for future development. Recent versions of the cabal toolchain (by which I mean Cabal, cabal-install and cabal-dev) allow for this sort of thing:

$ ls 
wx        wxcore          wxdirect
$ cabal-dev install --sandbox=<path-to-some-sandbox> ./wx ./wxcore ./wxdirect
...

(Note: I have not tested this with WX – kinks may arise that I’m unaware of!)

Assuming everything goes as expected, that will install the three packages from the local sub directories into the specified sandbox. Updating the source just means re-issuing a cabal-dev install command for the project that changed.

Keep in mind that you must either issue the repeated cabal-dev install commands in the correct order on your own, or you must use the batch command above and update version numbers accordingly.

I make no claims about this being ideal 😉 but I think it’s better than deleting the sandbox each time.