Many packages require ghc-7.8.x to build. But with the current logic we do not even try lts-2.x. For example, I just tried to init Haxl and it resulted in this:

None of the following snapshots provides a compiler matching your package(s):
    - lts-4.0
    - lts-3.19
    - nightly-2016-01-03
    - nightly-2015-11-17
    - lts-3.21
    - nightly-2016-01-08

Though it works with --resolver lts-2.22 . We should be trying at least one snapshot corresponding to each major version of ghc. Here we are trying all 7.10.x and no 7.8.x.