(filter f it)
  f: a callable
  it: an iterable
  returns an iter
F

Discards items from another iterator which fail to match a predicate.

Each time this iterator is advanced, it repeatedly calls (iter-next! it) until (f item) returns a value other than #f or #n. That item is then produced by the iterator.

(prn ..(filter even? '(1 2 3 4))) ; prints 2 4
map
zip