$ cabal-dev configure
Resolving dependencies...
cabal: internal error: unexpected package db stack
This is caused when you 'cabal-dev configure' that fails with/due to (?) a side effect.
Removing the 'dist' directory (and issuing a successfull configure, if needed) should get past this problem.
We have generally found that cabal-dev configure is unnecessary.
cabal-dev install is almost always sufficient to collect
dependencies, configure, build, and install (in a sandbox).
cabal-dev configure usually just adds confusion.
If you find a situation that needs cabal-dev configure please let
us know.