Comment by csande17

Imagine you were trying to explain the temperature-conversion program's behavior in the simplest, clearest way possible. (That is, after all, what programmers fundamentally do: try to explain things to computers as simply and clearly as possible.) You'd probably say something like: "When the user changes the Celsius textbox, the computer changes the Fahrenheit textbox to the converted value." And indeed, that's the program most people would write:

    celsiusTextbox.whenChanged do
        fahrenheitTextbox.value = cToF(celsiusTextbox.value)
    end

What you wouldn't say is something like: "The Fahrenheit textbox's value depends on whether the Fahrenheit textbox or the Celsius textbox was edited more recently. If the Fahrenheit textbox was edited more recently, its value is equal to the value the user entered into it most recently. If the Celsius textbox was edited more recently, the Fahrenheit textbox's value is equal to the converted value of the value the user entered into the Celsius textbox most recently." But that's the program you have to write in the "DCTP" approach proposed by the author.

I think this is true of a lot of UI programming: most people intuitively think about it in terms of "when X happens, do Y", so trying to cram it into another programming model is more trouble than it's worth.