What’s the equivalent of foldr, foldl in Emacs Lisp?

If you

(require 'cl)

then you can use the Common Lisp function reduce. Pass the keyword argument :from-end t for foldr.

ELISP> (reduce #'list '(1 2 3 4))
(((1 2) 3) 4)

ELISP> (reduce #'list '(1 2 3 4) :from-end t)
(1 (2 (3 4)))