Having defined our first generator, it is now time to see it in action. To run the generator, press the Generate button in the toolbar (or Ctrl+R or Generator | Generate from the menu bar). When prompted for the Graph to run the generator on, select ‘Simple’ (subsequent runs will remember this choice):

MetaEdit+ will now execute the generator for the selected graph and open a window with the generator output:

While it is not usually recommended to manually change the generator output, the Generator Output window nonetheless provides such elementary text editor features as cut/copy/paste, saving and printing. In many cases the Generator Output window is not opened at all, as the generator output is all written to a file; in that case a Generated Files window lists the resulting files, allowing you to look at their contents in MetaEdit+ or open them in their default application.

The Generator Editor also provides an advanced debugging toolset to ease generator development. The detailed documentation for the Generator Debugger can be found in Section 5.4; here we will just look briefly at its basic features. The debugger enables us to trace the execution of the generator line-by-line, set breakpoints at critical parts of our code, and view the current execution context stack as well as the variables and their values.

To debug the execution of a generator, start the generation by pressing the Debug button in the toolbar or selecting Generator | Debug... from the menu, and select the graph you want to execute the generator for from the list that opens (in our example, we pick ‘Simple’). The Generator Debugger will open, loaded with the code of the selected generator as shown in Figure 5–5:

The commands for tracing the generation execution are grouped on the left-hand side of the toolbar and in the Debug and Run menus, while the operations for setting and removing execution breakpoints can be found on the right-hand side of the toolbar or in the Breakpoint menu. To try them out, place the cursor at the beginning of the line that says

do ~From>()~To.State [Watch]

and press the Add Breakpoint button in the toolbar (or select Breakpoint | Add from the menu). This will place the breakpoint just before the do loop. Now, execute the generator up to this breakpoint by pressing Run button in the toolbar (or by selecting Run | Run). The Generator Debugger will now look like this:

As can be seen above, the Debugger Editor now shows an execution snapshot taken at the breakpoint. The next command to be executed is shown with selection highlighting next to the breakpoint in the Generator pane, while the various panes around it provide a view of the execution context and stacks. The generator output produced so far is shown in the Output pane. To proceed onwards step-by-step, press the Step Into button in the toolbar (or F5 or Debug | Step Into from the menu bar). While doing this, you will see the Output pane and other panes update, as more output is generated and the context changes according to the currently accessed model element. The other options provided for execution tracing are Step Over (F6 or Debug | Step Over), Step Out (F7 or Debug | Step Out), Run to Cursor (F8 or Debug | Run to Cursor), Run (F9 or Run | Run) and Break (F10 or Run | Break).

The Generator Editor and Debugger also provide several ways to use and manage the execution breakpoints. The toolbars on both tools provide simple buttons for adding and removing the toolbars and more advanced operations (like setting condition for the breakpoint or enabling/disabling them) can be found from the Breakpoint menu.