Executing GUIs
One of the most basic features of GUIKit is loading and executing an existing user interface application. This can be accomplished in one step in either a modal or modeless session with the Mathematica kernel using GUIRunModal or GUIRun.
Load the 
package before calling any GUIKit functions.
Here you load and execute an example user interface for a simple calculator that uses the Mathematica kernel for the calculations and, on closing, returns the results to the kernel.
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Here is a screen shot of what the previous interface would look like on a typical platform.
The GUIKit functions will search a path defined by the symbol $GUIPath to discover user interfaces so that only a short path to the definition is necessary.
Here is another example that provides an input dialog for entering angles. With both examples, a modal session with the kernel is initiated so that control and the result is only returned to the kernel when the user is finished.
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Here is a screen shot of what the previous user interface would look like on a typical platform.
You are also free to execute an interface in a modeless fashion. Executing the previous calculator example again with GUIRun immediately returns control to the kernel, but the calculator window continues to function. Also note that in a modeless session there is no way for the interface to return a custom result to the kernel when closed as the result value of the call to GUIRun.
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The next two sections explain the GUIObject expression that is returned from GUIRun and discuss some features of working with modeless windows. Also discussed is a technique of delaying the execution of the user interface, even if used with a modal session, so that you can customize its features before presenting it on screen.
