From d9aa8573f0145752b2ea33ff861847c4620cb1e9 Mon Sep 17 00:00:00 2001
From: Niklas Keller <me@kelunik.com>
Date: Wed, 11 May 2016 18:49:25 +0200
Subject: [PATCH] Throw InvalidArgumentException if argument to resolve() is
 neither callable nor an instance of Generator

---
 lib/functions.php | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/functions.php b/lib/functions.php
index d704144..b952313 100644
--- a/lib/functions.php
+++ b/lib/functions.php
@@ -757,10 +757,12 @@ function coroutine(callable $func) {
  */
 function resolve($generator) {
     if (!$generator instanceof \Generator) {
-        if (is_callable($generator)) {
-            $generator = call_user_func($generator);
+        if (!is_callable($generator)) {
+            throw new \InvalidArgumentException('Coroutine to resolve must be callable or instance of Generator');
         }
 
+        $generator = call_user_func($generator);
+
         if (!$generator instanceof \Generator) {
             throw new \LogicException('Callable passed to resolve() did not return an instance of Generator');
         }