Playground updates

website/src/playground/files/root/examples/useRange.ts

@@ -0,0 +1,23 @@
+// This program solves https://projecteuler.net/problem=2 using the `Range`
+// library. Range provides operations on iterables that are very similar to the
+// higher order functions on arrays. By using iterables, you can work with
+// infinite sequences (eg fibonacci), and the processing is done incrementally
+// instead of serializing each step into memory.
+
+import { Range } from "../lib/mod.ts";
+
+export default function main() {
+  return Range.from(fibonacci())
+    .while((x) => x < 4_000_000)
+    .filter((x) => x % 2 === 0)
+    .sum();
+}
+
+function* fibonacci() {
+  let [fibLast, fib] = [0, 1];
+
+  while (true) {
+    yield fib;
+    [fibLast, fib] = [fib, fibLast + fib];
+  }
+}