title: How can I print a message using a lambda in Kotlin
body: <p>I want to print <code>a()</code> message using lambda, but I can't do this. 
  printed Nothing in console. How can I do it?</p>
  
  <pre><code>var quackBehavior: QuackBehavior? = null
  
  fun a(){
      quackBehavior?.let{
          it("I want print this message")
      }
  }
  
  fun printMessage(){
      quackBehavior = {
          println(it)
      }
  }
  
  fun main() {
      a()
  }
  
  typealias QuackBehavior = (String) -&gt; Unit
  ``
  </code></pre>