#lang racket

#|
Max Sherman
CSE 341
Section 2

Things to do:
1. go over hw1
2. review recursive functions
3. lexical scope example
4. truthy falsy
5. delayed evaluation, function call semantics
6. streams if time

|#

;; function to convert celsius to farenheit (me)
(define (c->f ctemp) (+ (* 1.8 ctemp) 32))

;; write map (them)
; (define (map f xs) ....

;; convert list of temperatures
(define temps '(-40 20 30 100))
; (map c->f temps)
; or alternatively with a lambda
; (map (lambda (ctemp) (+ (* 1.8 ctemp) 32)) temps)

; lexical scope example
(define x 1)
(define (f)
  (let ([x 2]) (g)))
(define (g) x)
; what does (f) return?
; what if we change f so that it's (define (f) (set! x 2) (g))
; what if we also change g so that it's (define (g) (let ([y x]) y))


;; what values in racket are truthy and which are falsy?


;; function call semantics --> when called, the first thing functions do is
;; evaluate the expressions passed to them as arguments
(define (ident x) x)
; what does (ident (+ (* 4 5) 9)) do?
; what about (ident (factorial 5))
; what about (ident (begin (displayln "hi") 5))
(define (disregard-y x y) x)
; what does (disregard-y (begin (displayln "x") 1) (begin (displayln "y") 2)) do?
; how can we fix this if we dont want to print "y"?
; how can we write if in this way


;; streams
(define (nats)
  (define (aux n)
    (cons n (lambda () (aux (add1 n)))))
  (aux 0))

(define (print-stream s)
  (let ([pr (s)])
    (displayln (car pr))
    (print-stream (cdr pr))))