mkSort :: Integer -> Sort
mkSort i | 0 <= i = SortCtor i
         | otherwise = error "Negative index given to sort."
mkSort :: Integer -> Sort
mkSort i | 0 <= i = SortCtor i
         | otherwise = error "Negative index given to sort."
mkSort i | 0 <= i = SortCtor i
         | otherwise = error "Negative index given to sort."