{-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-}
unit sig where
    signature A where
        data T
        instance Show T
    module M where
        import A
        f :: T -> String
        f x = show x

unit mod where
    module A where
        type T = String

unit join where
    dependency sig[A=mod:A]
    dependency mod
    module S where
        import M
        g :: String -> String
        g x = f (x ++ "a")