drop_while(p, xs)
Return the suffix of the sequence xs remaining after removing elements that satisfy
the predicate p.
drop_while(is_positive, [1, 2, 3, -4, 5])
// [-4, 5]
function ints(n) n:~ints(n+1)
let s = ints(10)
take(3, drop_while(is_even, s))
// [11, 12, 13]