Added Typed Racket.

WTF this language actually sucks.

03-higher-order-functions/main.rkt~

@@ -0,0 +1,22 @@
+;; The first three lines of this file were inserted by DrRacket. They record metadata
+;; about the language level of this file in a form that our tools can easily process.
+#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname main) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
+; foo: (bar: A → A) → (A → A)
+(define (foo bar)
+  (local [(define (baz buzz)
+            (bar (bar buzz)))] baz))
+
+(check-expect ((foo add1) 1) 3)
+
+; goodies: (good?: A → Boolean, l: [A]) → [Index]
+; Returns a list of indices considered "good."
+(define (goodies good? l)
+  (local [; goodies/help: (good?: A → Boolean, l :[A], i: Int, a: [Index]) → [Index]
+          (define (goodies/help l i a)
+            (cond [(empty? l) (reverse a)]
+                  [(good? (first l)) (goodies/help (rest l) (add1 i) (cons i a))]
+                  [else (goodies/help (rest l) (add1 i) a)]))]
+    (goodies/help l 0 '())))
+
+(check-expect (goodies even? '(1 2 3 4 5)) '(1 3))
+(check-expect (goodies even? '()) '())