local :(copy-action) {}

(copy-action)!list obj cache:
	local :new []
	set-to cache obj new
	for i range 0 -- len obj:
		push-to new (deepcopy) @obj! i cache
	return new

(copy-action)!dict obj cache:
	local :new {}
	set-to cache obj new
	for key in keys obj:
		set-to new (deepcopy) @key cache (deepcopy) @obj! @key cache
	return new

labda obj cache:
	set-to cache @obj dup copy @obj
set-default (copy-action)

(deepcopy) obj cache:
	if has cache obj:
		return @cache! @obj
	(copy-action)! type @obj @obj cache

deepcopy obj:
	(deepcopy) obj {}

#example usage:
#a reasonably complicated object:
set :A { :foo [ "bar" ] [] [ & 1 2 & 3 4 ] }
set :B deepcopy A

!. A
!. B

push-to get-from B :foo "HODOR"

!. A
!. B

#it works with cycles:
set :C push-through dup []
set :D deepcopy C

!. C
!. D

push-to C 7

!. C
!. D