Is there a possibility to write a GUI from inside a function?

The Problem is: The callback of all GUI-functions work in the global workspace. But functions have their own workspace and can not access variables in the global workspace. Is there a possibility to make the GUI-functions use the workspace of the function?

function myvar = myfunc()
    myvar = true;
    h_fig = figure;

    % create a useless button
    uicontrol( h_fig, 'style', 'pushbutton', ...
                      'string', 'clickme', ...
                      'callback', 'myvar = false' );

    % wait for the button to be pressed
    while myvar
        pause( 0.2 );
    end

    close( h_fig );

    disp( 'this will never be displayed' );
end

This event-loop will run indefinitely, since the callback will not modify myvar in the function. Instead it will create a new myvar in the global workspace.