01-13.rkt

;; CIS352 notes -- 01/13
#lang racket

;; I can use define to define both values, and also functions
;; this is a value
(define foo 42)

;; Racket is expression-based, meaning that functions evaluate
;; their body expressions, and the result of evaluating any expression
;; is the computation's whole result...

(define (identity x) x)

;; To call a function, I write:
;; (f arg0 ...) <-- f is the name, arg0 and etc. are the arguments
(identity 20)

(define (bar x y)
  (+ (* x x) (* 2 y)))

(define (fac x)
  (if (equal? x 0) ;; don't use =, equal? is a check for structural equality
      1
      (* x (fac (- x 1)))))

;; How can we see that if isn't a function

;; Call-by-value: to evaluate a function, first evaluate its arguments, then
;; use those arguments to evaluate the body.

;; (f arg0 arg1 ...) -- each of arg0 arg1 etc.... have to be evaluated before f's body
;; may be evaluated. This is a fact in CBV languages. It's part of something called
;; "evaluation strategy." Sometimes it's also called an "eager" evaluation strategy

(define (loop) (loop))

(define (if-v e-g e-t e-f) (if e-g e-t e-f))
(if-v (equal? 2 2) "2 is equal? to 2" (loop))
(if (equal? 2 2) "2 is equal? to 2" (loop))