CSC151 2007S, Class 15: Recursion with Natural Numbers (2)

Admin:
* Reading for Friday: Local Bindings with let.
* EC: For supporting Grinnell's Ultimate Teams (Grinnellephants and
  Sticky Tongues) at their meet in Baton Rouge this weekend.
* EC: Track meet at UIowa Friday afternoon (3ish)

Overview:
* Q &  A.
* Lab.
* Reflection.

Problem, midway through the lab, iota

(define iota
  (lambda (n)
    (if (zero? n)
        null
	(cons n (iota (- n 1))))))   

Reflection - Why did I ask for the second definition of iota, in terms
of count-from?

* Remember that you can solve many problems by relying on previously
  solved problems.
* To point out a potential flaw in count-from - it doesn't work correctly if
  the upper bound is less than the lower bound
  * Worry about "boundary cases"

Nesting lists: Which is better?

(define nest
  (lambda (val depth)
    (if (zero? depth)
        val
	(list (nest val (- depth 1))))))

(define nest
  (lambda (val depth)
    (if (zero? depth)
        val
	(nest (list val) (- depth 1)))))