#lang racket
; sq : number -> number
(define (sq num) (* num num))

; f-to-c : number -> number
(define (f-to-c temp) (/ (- temp 32) 1.8))

; how-cold : integer -> string
(define (how-cold temp)
  (if (< (f-to-c temp) 0) "brrr" "could be worse"))

; pipe-surface-area : integer integer -> double
(define (pipe-surface-area length diameter)
  (* pi (* length diameter)))

; spanish-greeting : string -> string
(define (spanish-greeting name)
  (format "Hola ~a!" name))

; english-greeting : string -> string
(define (english-greeting name)
  (format "Hello ~a!" name))

; spanish? : string -> boolean
(define (spanish? language)
  (equal? language "spanish"))

; english? : string -> boolean
(define (english? language)
  (equal? language "english"))

; greet : string string -> string
(define (greet name language) (cond
                                [(spanish? language) (spanish-greeting name)]
                                [(english? language) (english-greeting name)]))

; add1 : integer -> integer
(define (add1 int)
  (+ int 1))

; list-length : list integer -> integer
(define (list-length list [count 0])
  (if (empty? list)
      count
      (list-length (cdr list) (add1 count))))

; search : list object -> integer
(define (search list item [index 0])
  (if (empty? list)
      -1
      (if (equal? (car list) item)
      index
      (search (cdr list) item (add1 index)))))

; sub1 : integer -> integer
(define (sub1 int)
  (- int 1))

; zero? : integer -> boolean
(define (zero? int)
  (equal? int 0))

; item-at : list integer -> object
(define (item-at list pos)
  (if (zero? pos) (car list) (item-at (cdr list) (sub1 pos))))

; first-and-last : list -> list
(define (first-and-last input)
  (list (car input) (item-at input (sub1 (list-length input)))))

; even? : integer -> boolean
(define (even? int)
  (equal? (remainder int 2) 0))

; just-the-evens : list list -> list
(define (just-the-evens input [result (list )])
  (if (empty? input)
      result
      (if (even? (car input))
          (just-the-evens (cdr input) (append result (list (car input))))
          (just-the-evens (cdr input) result))))

; select : list function list -> list
(define (select input filter [result `()])
  (if (empty? input)
      result
      (if (filter (car input))
        (select (cdr input) filter (append result (list (car input))))
        (select (cdr input) filter result))))

; odd? : integer -> boolean
(define (odd? int)
  (not (equal? (remainder int 2) 0)))

; triple-all : list list -> list
(define (triple-all lst [result `()])
  (if (empty? lst)
      result
      (triple-all (cdr lst) (append result (list (triple (car lst)))))))

; triple : integer -> integer
(define (triple int)
  (* int 3))

; sum : list -> integer
(define (sum lst)
  (apply + lst))

; sum-even-triples : list -> integer
(define (sum-even-triples lst)
  (sum (select (triple-all lst) even?)))

; contains-only-lower-case? : list boolean -> boolean
(define (contains-only-lower-case? lst [result #t])
  (if (empty? lst)
      result
      (if result
          (if (char-lower-case? (car lst))
              (contains-only-lower-case? (cdr lst) #t)
              (contains-only-lower-case? (cdr lst) #f))
          result)))

; map : list function -> list
(define (map lst fn [result `()])
  (if (empty? lst)
      result
      (map (cdr lst) fn (append result (list (fn (car lst)))))))

; greet-spanish : string -> string
(define (greet-spanish name)
  (greet name "spanish"))

; greet-english : string -> string
(define (greet-english)
  (lambda (name)
    (greet name "english")))

(sq 20)
(f-to-c 68)
(how-cold 68)
(pipe-surface-area 12 4)
(greet "Matthew" "english")
(greet "Cassie" "spanish")
(list-length `(1 2 3 4 5 6))
(search `(1 2 3) 1)
(search `(1 2 3) 5)
(item-at `(1 2 3 4 5) 4)
(first-and-last `(1 2 3 4 5 6 7 8 9 0))
(just-the-evens `(1 2 3 4 6 8 10 11 13 15 16))
(select `(1 2 3 4 6 8 10 11 13 15 16) even?)
(select `(1 2 3 4 6 8 10 11 13 15 16) odd?)
(sum `(1 2 3))
(triple-all `(1 2 3))
(sum-even-triples `(1 2 3 4 5 6))
(contains-only-lower-case? `(#\b #\c #\d #\a))
(contains-only-lower-case? `(#\b #\c #\d #\A))
(map `(1 2 3 4 5) triple)
((greet-english) "Cassie")
(greet-spanish "Mateo")