INTERNALS> (into (alexandria:alist-hash-table '((:a . 1) (:b . 2)))
                 (data-lens.transducers:mapping 'identity)
                 '((:c 3) (:d 4)))
#<hash-table :A: 1,
             :B: 2,
             :C: 3,
             :D: 4>
INTERNALS> (into #(1 2 3)
                 (data-lens.transducers:mapping (lambda (it)
                                                  (+ 4 it)))
                 '(0 1 2 -3))
#(1 2 3 4 5 6 1)
INTERNALS> (into '(1 2 3)
                 (data-lens.transducers:mapping (lambda (it)
                                                  (+ 4 it)))
                 #(0 1 2 -3))
(1 2 3 4 5 6 1)
INTERNALS> (into '(1 2 3)
                 (alexandria:compose (data-lens.transducers:filtering #'oddp)
                                     (data-lens.transducers:mapping (lambda (it) (+ 4 it))))
                 #(0 1 2 -3))
(1 2 3 5 1)