A-M baby

Task/Generator-Exponential/D/generator-exponential-2.d

@@ -0,0 +1,33 @@
+import std.stdio, std.traits;
+
+auto powers(in double e) pure nothrow {
+    double i = 0.0;
+    return () => i++ ^^ e;
+}
+
+auto filter(D)(D af, D bf) if (isCallable!D) {
+    double a = af(), b = bf();
+    return {
+        double r;
+        while (true) {
+            if (a < b) {
+                r = a;
+                a = af();
+                break;
+            }
+            if (b == a)
+                a = af();
+            b = bf();
+        }
+        return r;
+    };
+}
+
+void main() {
+    auto fgen = filter(powers(2), powers(3));
+    foreach (i; 0 .. 20)
+        fgen();
+    foreach (i; 0 .. 10)
+        write(fgen(), " ");
+    writeln();
+}