Racket fold

(foldr op id lst)

• op : a binary Racket Procedure
• lst : list of arguments
• Apply op right associatively to elements of a lst
• the identity element id is always used at the end
• Return result of evaluation

(foldl op id lst)

• op : a binary Racket Procedure
• lst : list of arguments
• Apply op left associatively to elements of a lst
• the identity element id is always used at the end
• Return result of evaluation

Example

• (foldr op id '()) => id
• (foldr op id '(e1 e2 ... em)) => (op e1 (op e2 (op ... (op en id))))
• (foldr + 0 '(1 2 3)) => (+ 1 (+ 2 (+3 0)))

Ideas

• fold and cons Correspondance