title: Create a ruby Proc from a string
body: <p>I want to define the block as a string, then create the lambda. 
  The following example does not work. 
  Is something like this possible?</p>
  
  <pre><code>code_string = "|x|x*2"
  
  l = lambda {eval(code_string)}
  
  l.call(3) =&gt; 6
  </code></pre>