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Task/Exponentiation-operator/EchoLisp/exponentiation-operator.echolisp

@@ -0,0 +1,25 @@
+;; this exponentiation function handles integer, rational or float x.
+;; n is a positive or negative integer.
+
+(define (** x n) (cond
+    ((zero? n) 1)
+    ((< n 0) (/ (** x (- n)))) ;; x**-n = 1 / x**n
+    ((= n 1) x)
+    ((= n 0) 1)
+    ((odd? n) (* x (** x (1- n)))) ;; x**(2p+1) = x * x**2p
+    (else (let ((m (** x (/ n 2)))) (* m m))))) ;; x**2p = (x**p) * (x**p)
+
+(** 3 0) → 1
+(** 3 4) → 81
+(** 3 5) → 243
+(** 10 10) → 10000000000
+(** 1.3 10) → 13.785849184900007
+
+(** -3 5) → -243
+(** 3 -4) → 1/81
+(** 3.7 -4) → 0.005335720890574502
+(** 2/3 7) → 128/2187
+
+(lib 'bigint)
+(** 666 42) →
+38540524895511613165266748863173814985473295063157418576769816295283207864908351682948692085553606681763707358759878656