Still nobody? Maybe I didn&#39;t write it clear. So one more time:<br><br>I have a list of numbers (say Int) <br>numberList = [1:Int,2,3,1,2,6,7,8] <br>and a number <br>sumOfNumberList = sum numberList <br>and here comes the question. Imagine the list numberLists is mutable (that&#39;s why in topic is &quot;not Haskell question&quot;) so the calculation doesn&#39;t occur only once but every time something changed in the list (listener pattern). (If the lis tis java List and Int is java Integer, every acces to list should trigger event to its listeners, but if I use list of another objects e.g. Item with value, every access to list should trigger event to its listeners as well as every modification of object Item should triggers its listeners (list) and that in turn triggers its listeners) How to make transformation of often used functions (map, sum, forall, filter, exists) to listeners in OO language? Is there anything (any tool, any paper, any blog...) about it?<br>
<br>Thanks<br><br>Fero<br><br>PS If nobody answers I really stop asking non Haskell questions in this mailling list:) <br>