title: compare two lists in tcl and obtain list of only differences between lists
body: <pre><code>proc ListComp { List1 List2 } {
  set DiffList {}
  foreach Item $List1 {
    if { [ lsearch -exact $List2 $Item ] == -1 } {
       lappend DiffList $Item
    }
  }
  foreach Item $List2 {
    if { [ lsearch -exact $List1 $Item ] == -1 } {
       if { [ lsearch -exact $DiffList $Item ] == -1 } {
          lappend DiffList $Item
       }
    }
  }
  return $DiffList
  }
  set diff [Listcomp $list1 $list2]
  puts diff
  </code></pre>
  <p>Input:</p>
  <pre><code>list1 {red, yellow, green, blue, orange}
  
  list2 {red, green, blue, orange}
  </code></pre>
  <p>expected output: <code>yellow</code></p>
  <p>output received:</p>
  <pre><code>                 yellow green
                   green blue
                   blue orange
                   orange
  </code></pre>
  <p>The search and match should be either ways. if length of list1 &gt; list2, the extra element in list1 should be printed. if length of list1 &lt; list2, the omitted element in list1 should be printed</p>