Update observable example

examples/observable.php

@@ -24,7 +24,8 @@
 $observable
     ->each(function ($value) {
         printf("Base: %d\n", $value);
-    })->done(
+    })
+    ->done(
         function () {
             printf("Base observable finished\n");
         },
@@ -37,30 +38,31 @@ function (Exception $exception) {
     $iter = $observable->getIterator();
     while (yield $iter->wait()) {
         printf("Coroutine: %d\n", $iter->getCurrent());
-        yield Coroutine\sleep(0.5);
+        yield Coroutine\sleep(0.5); // Artificial back-pressure on observable.
     }
 });
 $coroutine->done();
 
 $observable = $observable
     ->filter(function ($value) {
-        return $value % 2 === 0;
+        return $value % 2 === 0; // Only emit if $value is even.
     })
     ->map(function ($value) {
-        return pow(2, $value);
+        return pow(2, $value); // Emit 2 ^ $value.
     });
 
 
-$observable->each(
-    function ($value) {
+$observable
+    ->each(function ($value) {
         printf("Filtered and mapped: %d\n", $value);
-    },
-    function (Exception $exception) {
-        printf("Filtered and mapped error: %s\n", $exception->getMessage());
-    },
-    function () {
-        printf("Filtered and mapped observable finished\n");
-    }
-);
+    })
+    ->done(
+        function () {
+            printf("Filtered and mapped observable finished\n");
+        },
+        function (Exception $exception) {
+            printf("Filtered and mapped error: %s\n", $exception->getMessage());
+        }
+    );
 
 Loop\run();