- (atree-recurser recur-xpr base-xpr)syntax
anaphoric macro with internal symbols it, representing the current tree, go-left and go-right, representing traversal along cars and cdrs respectively. The result is a procedure, which recurs on its only list argument.
(define atcopy (atree-recurser (cons (go-left) (or (go-right) '())) it)) (atcopy '(1 (2 3 (4)) 5)) ; -> '(1 (2 3 (4)) 5)