mainUsedVars :: C.CEnv -> [Name]
mainUsedVars
    = map (\(C.Id name _) -> name)
    . maybe [] Set.toList
    . Map.lookup "main"
    . C._funUsedVars
mainUsedVars :: C.CEnv -> [Name]
mainUsedVars
    = map (\(C.Id name _) -> name)
    . maybe [] Set.toList
    . Map.lookup "main"
    . C._funUsedVars
mainUsedVars
    = map (\(C.Id name _) -> name)
    . maybe [] Set.toList
    . Map.lookup "main"
    . C._funUsedVars