#eng-learning

SICP Ch. 1.1

Big picture thinking about the programming process
Abstraction and building software from general patterns
Functions as data
Contains three programming paradigms (functional, OOP, declarative)

Scheme

ALGOL

Why Scheme?

Procedures as data
It's simple

(* 25 4 12)
1200

(+ (* 3 (+ (* 2 4) (+ 3 5))) (+ (- 10 7) 6))

(+ (* 3
      (+ (* 2 4)
         (+ 3 5)))
   (+ (- 10 7)
      6))

(* (+ 2 (* 4 6))
   (+ 3 5 7))

Procedures

(define (square x) (* x x))

(define (square  x)        (*         x     x))
  |        |     |          |         |     |
 To     square something, multiply   it by itself

Interpreter & Substitution

(sum-of-squares (+ 5 1) (* 5 2))

(+ (square 6) (square 10))

(+ (* 6 6) (* 10 10))

(+ 36 100)

136

Interpreter & Substitution

(sum-of-squares (+ 5 1) (* 5 2))

(+    (square (+ 5 1))      (square (* 5 2))  )

(+    (* (+ 5 1) (+ 5 1))   (* (* 5 2) (* 5 2)))

(+         (* 6 6)             (* 10 10))

(+           36                   100)

                    136

Normal-Order Evaluation

Conditionals

(define (abs x)
  (cond ((> x 0) x)
        ((= x 0) 0)
        ((< x 0) (- x))))
        
(define (abs x)
  (cond ((< x 0) (- x))
        (else x)))
            
(define (abs x)
  (if (< x 0)
      (- x)
      x))

Block Structure

(define (sqrt x)
  (define (good-enough? guess x)
    (< (abs (- (square guess) x)) 0.001))
  (define (improve guess x)
    (average guess (/ x guess)))
  (define (sqrt-iter guess x)
    (if (good-enough? guess x)
        guess
        (sqrt-iter (improve guess x) x)))
  (sqrt-iter 1.0 x))

"... programmer's must learn to understand and to anticipate the consequences of their conjuring."

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