https://np.reddit.com/r/haskell/comments/msz3hr/megaparsec_asking_for_advice_on_a_parsing_problem/guygauv/

I came up with this:

partitionTopLevelStatements :: [TopLevelStatement] -> ([ImportStatement], [PackageDefinition])
partitionTopLevelStatements = foldr acc init
  where
    init = ([], [])
    acc (ImportStmt e) (imports, packages) = (e : imports, packages)
    acc (PackageDef e) (imports, packages) = (imports, e : packages)