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/*!
    \example script/calculator
    \title QtScript Calculator Example
    \ingroup scripting

    In this simple QtScript example, we show how to implement the
    functionality of a calculator widget.

    \image qtscript-calculator-example.png

    The program logic in this example is a fairly straight port of the logic in the C++ \l{Calculator Example}.
    The graphical user interface is defined in a UI file.

    The C++ part of the example consists of four steps:
    \list
    \o Evaluate the script code that defines the \c{Calculator} class.

    \snippet examples/script/calculator/main.cpp 0a
    \snippet examples/script/calculator/main.cpp 0b

    \o Create a widget from the UI file using QUiLoader.

    \snippet examples/script/calculator/main.cpp 1

    \o Call the Calculator constructor function to create a new \c{Calculator} script object, passing the widget as argument.

    \snippet examples/script/calculator/main.cpp 2

    \o Show the widget and start the application event loop.

    \snippet examples/script/calculator/main.cpp 3

    \endlist

    On the script side, the \c{Calculator} constructor function
    initializes the instance variables of the new \c{Calculator}
    object, and connects the clicked() signal of the form's buttons
    to corresponding functions defined in the \c{Calculator} prototype
    object; the effect is that when a button is clicked, the proper
    script function will be invoked to carry out the operation.

    \snippet examples/script/calculator/calculator.js 0

    A \c{Calculator} object is just a plain script object; it is not
    a widget. Instead, it stores a reference to the calculator form
    (the widget) in an instance variable, \c{ui}. The calculator
    script functions can access components of the form by referring
    to the proper children of the \c{ui} member.

    \snippet examples/script/calculator/calculator.js 1

    The digitClicked() function uses the special local variable
    __qt_sender__ to access the object that triggered the signal;
    this gives us a simple way to retrieve the value of the digit
    that was clicked.

    \snippet examples/script/calculator/calculator.js 2

    The changeSign() function shows how we retrieve the text property
    of the calculator's display, change it appropriately, and write
    back the new value.


*/