Emphasize similarities between traversalVL and foldVL

optics-core/src/Optics/Fold.hs

@@ -117,14 +117,17 @@ import Optics.Internal.Utils
 -- | Type synonym for a fold.
 type Fold s a = Optic' A_Fold NoIx s a
 
--- | Obtain a 'Fold' by lifting 'traverse_' like function.
+-- | Construct a 'Fold' from a 'traverse_' like function.
+--
+-- /Note:/ for lifting a 'Data.Traversable.traverse' like function see
+-- 'Optics.Traversal.traversalVL'.
 --
 -- @
 -- 'foldVL' '.' 'traverseOf_' ≡ 'id'
 -- 'traverseOf_' '.' 'foldVL' ≡ 'id'
 -- @
 foldVL
-  :: (forall f. Applicative f => (a -> f u) -> s -> f v)
+  :: (forall f. Applicative f => (a -> f b) -> s -> f ())
   -> Fold s a
 foldVL f = Optic (foldVL__ f)
 {-# INLINE foldVL #-}

optics-core/src/Optics/Traversal.hs

@@ -124,13 +124,18 @@ type TraversalVL s t a b = forall f. Applicative f => (a -> f b) -> s -> f t
 -- | Type synonym for a type-preserving van Laarhoven traversal.
 type TraversalVL' s a = TraversalVL s s a a
 
--- | Build a traversal from the van Laarhoven representation.
+-- | Construct a 'Traversal' from a 'traverse' like function.
+--
+-- /Note:/ for lifting a 'Data.Foldable.traverse_' like function see
+-- 'Optics.Fold.foldVL'.
 --
 -- @
 -- 'traversalVL' '.' 'traverseOf' ≡ 'id'
 -- 'traverseOf' '.' 'traversalVL' ≡ 'id'
 -- @
-traversalVL :: TraversalVL s t a b -> Traversal s t a b
+traversalVL
+  :: (forall f. Applicative f => (a -> f b) -> s -> f t)
+  -> Traversal s t a b
 traversalVL t = Optic (wander t)
 {-# INLINE traversalVL #-}