new files

Task/Assertions/Racket/assertions-1.rkt

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+#lang racket
+
+(define/contract x
+  (=/c 42) ; make sure x = 42
+  42)
+
+(define/contract f
+  (-> number? (or/c 'yes 'no)) ; function contract
+  (lambda (x)
+    (if (= 42 x) 'yes 'no)))
+
+(f 42)    ; succeeds
+(f "foo") ; contract error!