9 instance peano Z where peano = Z
10 instance peano (S a) | peano a where peano = S peano
12 class peanoplus a b ~c
16 instance peanoplus a Z a | peano a
20 :: FString n = FS [Char]
25 fappend :: (FString a) Char -> FString (S a) | peano a
26 fappend (FS l) c = FS (l ++ [c])