Is there an application of foldr where the resulting expression evaluates to an identical copy of the original list?

Question

Hey so I have kind of been struggling with this question, i've been playing around with different combinations but I cannot seem to think of a function that will cause the list to produce itself. Does anyone have an idea?

Answer 1

Sure, it's pretty straightforward. You just have to use the same procedure that was used to construct the list in the first place: cons.

(define lst '(1 2 3 4 5))
(foldr cons '() lst)
=> '(1 2 3 4 5)