add ref function alias to closure from callable

src/functions.php

@@ -32,6 +32,11 @@ function predicate($predicate): Predicate
     }
 }
 
+function ref(callable $callable)
+{
+    return \Closure::fromCallable($callable);
+}
+
 function not($predicate)
 {
     return predicate($predicate)->not();