NoMatchErr.hs:20:12:
    Could not deduce (Memo d0 ~ Memo d)
    from the context (Fun d)
      bound by the type signature for f :: Fun d => Memo d a -> Memo d a
      at NoMatchErr.hs:20:1-15
    NB: `Memo' is a type function, and may not be injective
    Expected type: Memo d a
      Actual type: Memo d0 a
    Expected type: Memo d a -> d0 -> a
      Actual type: Memo d0 a -> d0 -> a
    In the second argument of `(.)', namely `appl'
    In the expression: abst . appl