feat(rstream): add tweenNumber()

packages/rstream/src/tween.ts

@@ -78,3 +78,28 @@ export const tween = <T>(
         scan(reducer(() => initial, (acc, { src }) => mix(acc, src))),
         dedupe(stop || (() => false))
     );
+
+/**
+ * Convenience version of `tween` for its most common use case, tweening
+ * of numeric streams.
+ *
+ * @param src
+ * @param init
+ * @param speed
+ * @param eps
+ * @param clock
+ */
+export const tweenNumber = (
+    src: ISubscribable<number>,
+    init = 0,
+    speed = 0.05,
+    eps = 1e-3,
+    clock?: ISubscribable<any> | number
+) =>
+    tween<number>(
+        src,
+        init,
+        (a, b) => a + (b - a) * speed,
+        (a, b) => Math.abs(a - b) < eps,
+        clock
+    );