CSC151.02 2003F, Class 38: Higher-Order Procedures, Concluded (Temporarily)

Admin
* Revamped schedule.  Project dropped (probably).
* Monday: Discuss exam
* Reading (for Tuesday): Variable-Arity procedures
* Lab writeup also due Tuesday

Overview:
* Work on the lab.
* Reflect.

Remember: Named Let is a "cool shorthand" for "define and call recursive
procedure"

(define sum
  (lambda (lst)
    (letrec ((kernel (lambda (remaining tmp)
            (if (null? remaining)
                tmp
                (kernel (cdr remaining) (+ tmp (car remaining)))))))
      (kernel lst 0))))

Here's another, very similar, version 

(define sum
  (lambda (lst)
    (letrec ((kernel (lambda (remaining tmp)
            (if (null? remaining)
                tmp
                (kernel (cdr remaining) (+ tmp (car remaining)))))))
      (kernel (cdr lst) (car lst)))))