cabal new-build: what does foo-setup~> mean?

Hi, How should I interpret the following dependency solving error from cabal new-build? Resolving dependencies... cabal: Could not resolve dependencies: trying: time-setup.time~>entropy-setup.time-1.1.2.3 (dependency of time-1.1.2.3) trying: time-setup.Cabal~>entropy-setup.Cabal-1.20.0.4 (dependency of time-1.1.2.3) Dependency tree exhaustively searched. FWIW I'm trying to build the HTTP package with GHC 7.0 and the following options. The solver takes ~10 minutes before failing. --constraint 'time==1.1.2.3' --constraint 'entropy<0.2.2.4' -f-warp-tests --constraint 'HUnit<1.4' cabal configure does seem to be able to find a solution. Cheers, Ganesh