- = case [ p | p <- all_pkgs, pkgarg `matchesPkg` p ] of
- [] -> dieWith 2 ("cannot find package " ++ pkg_msg pkgarg)
+ = fmap (concatMap snd) $ findPackagesByDB db_stack pkgarg
+
+findPackagesByDB :: PackageDBStack -> PackageArg
+ -> IO [(NamedPackageDB, [InstalledPackageInfo])]
+findPackagesByDB db_stack pkgarg
+ = case [ (db, matched)
+ | db@(db_name,pkgs) <- db_stack,
+ let matched = filter (pkgarg `matchesPkg`) pkgs,
+ not (null matched) ] of
+ [] -> die ("cannot find package " ++ pkg_msg pkgarg)