Add lab 4 content.

labs/L04/application.rkt

@@ -0,0 +1,4 @@
+#lang racket
+(require "hello.rkt")
+(require rackunit)
+(hello)

labs/L04/functions-as-values.rkt

@@ -0,0 +1,15 @@
+#lang slideshow
+(define (series mk)
+  (hc-append 4 (mk 5) (mk 10) (mk 20)))
+
+(define (series2 mk)
+  (apply hc-append 4 (map mk '(5 10 20))))
+
+(define (series3 mk)
+  (apply hc-append 1 (build-list 100 mk)))
+
+(module+ test
+  (require rackunit)
+  (require racket/serialize)
+  (check-equal? (serialize (series circle)) (serialize(series2 circle))))
+

labs/L04/hello.rkt

@@ -0,0 +1,11 @@
+(module hello racket
+  (provide hello)
+  (define (hello) (displayln "Hello world!"))
+
+(module+ test 
+  (require rackunit)
+  (check-equal? (with-output-to-string hello) "Hello world!\n")
+  (check-equal? (with-output-to-string hello) (begin (sleep 3) "Hello world!\n")))
+
+(module+ main
+  (hello)))

labs/L04/recursion.rkt

@@ -0,0 +1,9 @@
+    #lang racket
+    (define (fact n)
+      (cond
+        [(zero? n) 1]
+        [else (* n (fact (sub1 n)))]))
+
+    (module+ test
+      (require rackunit)
+      (check-equal? (fact 10) 3628800))