September 2017 Update

Task/Metaprogramming/Racket/metaprogramming-1.rkt

@@ -0,0 +1,10 @@
+#lang racket
+
+(define-syntax-rule (list-when test body)
+  (if test
+      body
+      '()))
+
+(let ([not-a-string 42])
+  (list-when (string? not-a-string)
+    (string->list not-a-string)))

Task/Metaprogramming/Racket/metaprogramming-2.rkt

@@ -0,0 +1,8 @@
+(require (for-syntax syntax/parse))
+
+(define-syntax list-when
+  (syntax-parser
+    [(_ test:expr body:expr)
+     #'(if test
+           body
+           null)]))