until -package:numeric-prelude -package:base-prelude -package:distribution-opensuse -package:Cabal -package:xmonad-contrib -package:rebase -package:ghc-lib-parser -package:clash-prelude package:dunai

Similar to Yampa's delayed switching. Loses a b in case of an exception.
Run the first msf until the second one produces True from the output of the first.