[f] [f coll] [f c1 c2] [f c1 c2 c3] [f c1 c2 c3 & colls]
Returns an eagerly evaluated vector of the results of applying
f to the set of first items of each coll, followed by applying
f to the set of second items in each coll, until any one of the colls is exhausted.
Any remaining items in other colls are ignored.
f should accept number-of-colls arguments.
Returns a transducer when no collections are provided.
mapv is identical to clj::clojure.core/map except that where
map generates a lazy sequence,
mapv is eager. Thus while side-effects in a
map operation aren't a great idea, they are at least predictable within a
mapv where they may not be in a