title: Editing tuples in a list of sml
body: <p>I want to make a list which is of specification :(string*int) list and the tuples can be edited. For example, suppose</p>
  
  <pre><code>val gamma = [("a",20),("b",30),("c",40)] :(string*int) list
  </code></pre>
  
  <p>Now, how can I change the value <code>30</code> in the tuple <code>("b",30)</code> to , let's say, 70.</p>