Hi, A few weeks ago during the Hackathon in Gothenburg I started working on a library for decision diagrams. The purpose was to use it in cabal-install when figuring out which packages should be installed and which version of them to choose. Why do we need something as complex as decision diagrams for that? Simply because the problem is NP-complete in general. Now, heuristics might do a good job at solving this problem but it might be wise to have something like this library as a fall-back. So, I'm happy to announce the first version of my decision diagram library. The darcs repo can be found here: http://www.cs.chalmers.se/~josefs/decisiondiagram The status of the library is as follows: I'm beginning to trust the correctness of the implementation. There are a few tests in place and although I have more tests in mind the testing that I have already done gives me quite a bit of confidence. As to the speed of the library: it's pretty poor. I've used most of the tricks in the book on implementing decision diagrams so complexity wise it should be like any other BDD implementation except for a few log factors here and there. But I haven't cared anything about constant factors, so the wall clock performance is pretty weak. As a benchmark I wrote a small sudoku solver but my library choked on even an easy puzzle. I nevertheless feel that this library is a good starting point and that it will be able to handle all current packages that we have easily. I am aware that the is a GSOC project coming up which is supposed to tackle this issue as well. This package is by no means meant to supersede that project before it has begun. I think we can benefit from several approaches here since the underlying problem is NP-complete and thus it's probably wise to evaluate more than one option. I haven't looked into how to use this package in cabal-install yet, but I suspect it will be fairly easy. I'd appreciate any comments and help on that though since I'm not familiar with the cabal-install code base yet. Happy cabaling, Josef