buildSub :: Sub a (a -> r) -> Sub a r
buildSub (Sub i f k) = Sub (i + 1) f (k (f i))
buildSub :: Sub a (a -> r) -> Sub a r
buildSub (Sub i f k) = Sub (i + 1) f (k (f i))
buildSub (Sub i f k) = Sub (i + 1) f (k (f i))