Notes from SICP using Scheme (LISP)

Scheme_Notes

;; Installation on Mac OS X
;; After downloading and installing into applications folder run the following commands from the terminal
;; sudo ln -s /Applications/MIT\:GNU\ Scheme.app/Contents/Resources /usr/local/lib/mit-scheme-x86-64
;; sudo ln -s /usr/local/lib/mit-scheme-x86-64/mit-scheme /usr/bin/scheme
;; To Launch simply type "scheme" in the terminal

;; Using operators on operands (Scheme uses prefix notation)
(+ 4 4) ; Add 4 + 4 = 8

;; Add two numbers that are multiplied
(+ (* 2 4) (* 2 4)) ; 2 * 4 + 2 * 4 = 16

;; Assigning a variable a value
(define size 2)
(* 5 size)

(define pi 3.14159)
(define radius 10)
(define circumference (* 2 pi radius))

;; Compund procedure
(define (square x) (* x x))

(square 2) ; 2 * 2 = 4

;; Compound procedure as a building block
(define (sum-of-squares x y)
  (+ (square x) (square y)))
  
(sum-of-squares 2 2) ; 2 * 2 + 2 * 2 = 8

;; Case analysis or Conditional
(define (abs x)
  (cond ((> x 0) x)
        ((= x 0) 0)
        ((< x 0) (-x))))
        

;; or another way
(define (abs x)
  (cond ((< x 0) ( - x))
        (else x)))
        
;; If Expression
(define (abs x)
  (if (< x 0)
      (- x)
      x))

;; Primitive predicates <, >, =
;; Logical composition operations and, or, not
(and (> x 5) (< x 10))

;; Define a new predicate
(define (>= x y)
  (or (> x y) (= x y)))
  
;; or alternative
(define (>= x y)
  (not (< x y)))