Data commit

Task/Church-numerals/Racket/church-numerals.rkt

@@ -0,0 +1,36 @@
+#lang racket
+
+(define zero (λ (f) (λ (x) x)))
+(define zero* (const identity)) ; zero renamed
+
+(define one (λ (f) f))
+(define one* identity) ; one renamed
+
+(define succ (λ (n) (λ (f) (λ (x) (f ((n f) x))))))
+(define succ* (λ (n) (λ (f) (λ (x) ((n f) (f x)))))) ; different impl
+
+(define add (λ (n) (λ (m) (λ (f) (λ (x) ((m f) ((n f) x)))))))
+(define add* (λ (n) (n succ)))
+
+(define succ** (add one))
+
+(define mult (λ (n) (λ (m) (λ (f) (m (n f))))))
+(define mult* (λ (n) (λ (m) ((m (add n)) zero))))
+
+(define expt  (λ (n) (λ (m) (m n))))
+(define expt* (λ (n) (λ (m) ((m (mult n)) one))))
+
+(define (nat->church n)
+  (cond
+    [(zero? n) zero]
+    [else (succ (nat->church (sub1 n)))]))
+
+(define (church->nat n) ((n add1) 0))
+
+(define three (nat->church 3))
+(define four (nat->church 4))
+
+(church->nat ((add three) four))
+(church->nat ((mult three) four))
+(church->nat ((expt three) four))
+(church->nat ((expt four) three))