A-M baby

Task/Generator-Exponential/Common-Lisp/generator-exponential.lisp

@@ -0,0 +1,21 @@
+(defun take (seq &optional (n 1))
+  (values-list (loop repeat n collect (funcall seq))))
+
+(defun power-seq (n)
+  (let ((x 0))
+    (lambda () (expt (incf x) n))))
+
+(defun filter-seq (s1 s2) ;; remove s2 from s1
+  (let ((x1 (take s1)) (x2 (take s2)))
+    (lambda ()
+      (tagbody g
+	(if (= x1 x2)
+	     (progn (setf x1 (take s1) x2 (take s2)) (go g)))
+	(if (> x1 x2)
+	     (progn (setf x2 (take s2)) (go g))))
+
+      (prog1 x1 (setf x1 (take s1))))))
+
+(let ((2not3 (filter-seq (power-seq 2) (power-seq 3))))
+  (take 2not3 20) ;; drop 20
+  (princ (multiple-value-list (take 2not3 10))))