(require "combinators.BRU" "list-comprehension-basics.MRU")
[(map (Y map-impl))
; base-case-value: value to be returned when the list is empty.
; combiner: to combine the var with the result of the recursive call.
; ls: the list.
 (fold (Y fold-impl))
 (length (Y length-impl))
 (zip (Y zip-impl))]
; (length (\l (fold 0 + (map (lambda (item) 1) l))))