#lang racket

;; CSE 413 19wi
;; Lecture 7 sample code
;; Environments and closures
;; Hal Perkins

(define nums '(1 2 3 4 5))
(define rnums '(17 3 -2 42 15 3 12))
(define alist '(a (b c) d e))
(define x 17)
(define y 42)

(define (incr n) (+ 1 n))
(define (dbl n)  (* 2 n))

;; expressions & global variables
(+ x 1)

;; let and let* expressions
;; same environments, difference is which environment is
;; searched first in initialization
(let ([x 2]
      [y (+ 1 x)])
  (+ x y))

(let* ([x 2]
       [y (+ 1 x)])
  (+ x y))

;; A function is a closure <code,env>
;; (lambda ...) evaluates to a closure
;; whose environment env references the
;; environment where lambda was evaluated

;; function call:
;;   1) Create new environment whose parent is
;;      env from closure
;;   2) Bind parameter names to values in new environment
;;   3) Evaluate function in this environment

;; simple function closures
(define plus (lambda (x y) (+ x y)))

;; function closure with global names
(define plusx (lambda (n) (+ x n)))

;; (plusx 2)