ss_booleans.rkt

#lang simply-scheme

(define (greet name)
  (if (equal? (first name) 'professor)
      (se '(i hope i am not bothering you) 'professor (last name))
      (se '(good to see you) (first name))))

(greet '(matt wright))

(greet '(professor harold abelson))

(member? 'mick '(dave dee dozy beaky mick and tich))

(member? 'mick '(john paul george ringo))

(member? 'e 'truly)

(member? 'y 'truly)

(= 3 4)

(= 67 67)

(= (+ 52 8) 60)

(> 98 97)

(before? 'zorn 'coleman)

(before? 'pete 'ringo)

(empty? '(abbey road))

(empty? '())

(empty? 'hi)

(empty? (bf (bf 'hi)))

(empty? "")

(number? 'three)

(number? 74)

(boolean? #f)

(boolean? '(the beatles))

(boolean? 234)

(boolean? #t)

(word? 'flying)

(word? '(dig it))

(word? 87)

(sentence? 'wait)

(sentence? '(what goes on))

(define (vowel? letter)
  (member? letter 'aeiou))

(define (positive? number)
  (> number 0))

; using predicates

(define (abs num)
  (if (< num 0)
      (- num)
      num))

(define (divisible? big little)
  (= (remainder big little) 0))

(define (buzz num)
  (if (or (divisible? num 7) (member? 7 num))
      'buzz
      num))

(buzz 17)
(buzz 42)
(buzz 124)

;(define (plural wd)
;  (word wd 's))

(plural 'beatle)

(plural 'computer)

(plural 'fly) ; ah, but incorrect. how do we make this correct?

(define (plural wd)
  (if (equal? (last wd) 'y)
      (word (bl wd) 'ies)
      (word wd 's)))

(plural 'beatle)

(plural 'computer)

(plural 'fly)

; special forms

; if is a special form

(if (= 3 3)
    'sure
    (factorial 1000))
    
; and & or are also special forms

(define (divisible? big small)
  (= (remainder big small) 0))

(define (num-divisible-by-4? x)
  (and (number? x) (divisible? x 4)))

(num-divisible-by-4? 16)

(num-divisible-by-4? 6)

(num-divisible-by-4? 'aardvark)

(divisible? 'aardvark 4)

; everything that isn't false is true

(define (divisible? big little)
  (= (remainder big little) 0))

(if (+ 3 4) 'yes 'no)

(define (integer-quotient big little)
  (if (divisible? big little)
      (/ big little)
      #f))

(integer-quotient 27 3)

(integer-quotient 12 5)

; returns a true result as soon as it evaluates true
(or #f 3 #f 4)

; returns a true result only if all arguments are true
(and 1 2 3 4 5)

(define (integer-quotient big little) ; alternate version
  (and (divisible? big little)
       (/ big little)))

(define (roman-value letter)
  (if (equal? letter 'i)
      1
      (if (equal? letter 'v)
          5
          (if (equal? letter 'x)
              10
              (if (equal? letter 'l)
                  50
                  (if (equal? letter 'c)
                      100
                      (if (equal? letter 'd)
                          500
                          (if (equal? letter 'm)
                              1000
                              'huh?))))))))

(define (roman-value letter)
  (cond ((equal? letter 'i) 1)
        ((equal? letter 'v) 5)
        ((equal? letter 'x) 10)
        ((equal? letter 'l) 50)
        ((equal? letter 'c) 100)
        ((equal? letter 'd) 500)
        ((equal? letter 'm) 1000)
        (else 'huh?)))

(define (truefalse value)
  (cond (value 'true)
        (else 'false)))

(truefalse (= 2 (+ 1 1)))

(truefalse (= 5 (+ 2 2)))
           
; most restrictive test goes first

(cond ((number? (first sent)) &hellip) 
      ((empty? sent) &hellip)
      & hellip) 

;; wrong, because the first test only makes sense once you've established that there is a first word of the sentence

(cond ((empty? sent) &hellip)
      ((and (not (empty? sent)) (number? (first sent))) &hellip)
      &hellip)

;; this is also unnecessary because the sentence is nonempty once we get as far as the second clause

; if is composable

(define (greet name)
  (if (equal? (first name) 'professor)
      (se '(pleased to meet you)
          'professor
          (last name)
          '(- how are you?))
      (se '(pleased to meet you)
          (first name)
          '(- how are you?))))

(greet '(brian epstein))

(greet '(professor donald knuth))
                          
(define (greet name)
  (se '(pleased to meet you)
      (if (equal? (first name) 'professor)
          (se 'professor (last name))
          (first name))
      '(- how are you?)))