6.090 IAP 05 Lecture 3

Names

Ask Questions:
how long for homework
more breaks during class?

Answer Questions:
"real scheme programs" instead of line by line
is scheme used in the real world?

Homework:
(op green *)

lambda tomfoolery
 - variables into and out of, lambdas of no arguments

Stepper:
M-s to start
<space> to advance

C-x k to kill buffer when done

warm up
(define abs
  (lambda (x)
    (if (< x 0)
        (- x)
        x)))

go over even?

more recursive procedures

sum 1..n
(+ shortcut)

compute e

compute pi?

towers of hanoi

download and load file lec3.scm
commentary about style

(define move
  (lambda (disk from to)
    (format #t "move disc ~A from ~A to ~A~%" disc from to)))

(define (hanoi n from to swap)
  (if (= n 1)
      (move n from to)
      (begin
       (hanoi (- n 1) from swap to)
       (move n from to)
       (hanoi (- n 1) swap to from))))

syntactic sugar - define & lambda

let

guessing game