[Haskell-cafe] jswm - how to manipulate strings?

[Andrew U. Frank]

i try to use jswm to build some web applications, but i got quickly
        stuck. I used the example programs provided and tried to change
        them.
        starting with the calculator, i would like to use the string
        that the
        user puts in and apply a function to it (say transform it to
        capitals,
        later i want to do more complex operations). now i cannot find a
        way to
        apply a function to the type returned from the input: 
        
        get'value ::
                  (Monad mn, CHTMLTextAreaElement this) =>
                    Expression this -> mn (Expression String)
        
        
        how can i apply some function to the string in the input : mn
        (Expression String) ? or how can i get the string out such that
        i can
        change it and later put it back into an expression?
        
        help is appreciated - there seems to be only a small piece
        missing..
        
        andrew