Adding in a port of Dan Gulotta's "The Halting Problem" .clj script.

eg/nonfree/halting-problem/halting.hy

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+; Very much a knockoff (straight port) of Dan Gulotta's 2013 MIT Mystery Hunt
+; puzzle "The Halting Problem".
+
+
+(defn evaluate [f] ((f (lambda [x] (+ x 1))) 0))
+
+(defn successor [n] (lambda [f] (lambda [x] (f ((n f) x)))))
+(defn plus [m n] ((n successor) m))
+(defn exponent [m n] (n m))
+(defn zero [f] (lambda [x] x))
+(defn one [f] (lambda [x] (f x)))
+
+(defn predecessor [n] (lambda [f] (lambda [x]
+  (((n (lambda [g] (lambda [h] (h (g f))))) (lambda [y] x)) (lambda [z] z)))))
+
+(defn subtract [m n] ((m predecessor) n))
+
+(def two (plus one one))
+(def three (plus two one))
+
+(print (evaluate (exponent three three)))