O(n) Map each element of the structure to a monoid and combine
the results. It uses the same implementation as the corresponding
method of the Foldable type cless. Note that it's implemented
in terms of foldr and won't fuse with functions that traverse
the vector from left to right (map, generate, etc.).
O(n) Like foldMap, but strict in the accumulator. It
uses the same implementation as the corresponding method of the
Foldable type class. Note that it's implemented in terms of
foldl', so it fuses in most contexts.