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Task/Generator-Exponential/EchoLisp/generator-exponential.echolisp

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+(lib 'tasks) ;; for make-generator
+
+;; generator of generators
+(define (gen-power power)
+	(make-generator
+		(lambda(n) (yield (expt n power)) (1+ n))  1))
+		
+(define powers-2 (gen-power 2))
+(define powers-3 (gen-power 3))
+
+(take powers-3 10)
+    → (1 8 27 64 125 216 343 512 729 1000)
+
+;; generators substraction
+;; input : two generators ga, gb - Sequences must be increasing
+;; output : new generator  = ga sequence minus gb sequence
+
+(define (gen-substract ga gb)
+	(define (substract b (a))
+	(set! a (next ga))
+	(while (>= a b) ; avance b until > a
+		(when (= a b) (set! a (next ga)))
+		(set! b (next gb)))
+	(yield a)
+	b ) ;; b := next state
+	(make-generator substract (next gb)))
+
+;; application
+(define task    (gen-substract (gen-power 2) (gen-power 3)))
+
+(drop task 20)
+(take task 10)
+    → (529 576 625 676 784 841 900 961 1024 1089)
+
+; inspect
+task → #generator:state: 1331