title: Check if a value is in a list
body: <p>Does Go have something similar to Python's <code>in</code> keyword? I want to check if a value is in a list.</p>
  
  <p>For example in Python:</p>
  
  <pre><code>x = 'red'
  
  if x in ['red', 'green', 'yellow', 'blue']:
      print "found"
  else:
      print "not found"
  </code></pre>
  
  <p>In Go I've come up with using the set idiom but I don't think it's ideal as I have to specify a int value that I'm not using.</p>
  
  <pre><code>x := "red"
  
  valid := map[string]int{"red": 0, "green": 0,"yellow": 0, "blue": 0}
  
  if _, ok := valid[x]; ok {
      fmt.Println("found")
  } else {
      fmt.Println("not found")
  }
  </code></pre>
  
  <p>I understand having an <code>in</code> keyword is probably related to generics. Is there a way to do this using go generate or something?</p>