Debugging your grammars

In this section, you will learn more about debugging ANTLR grammars in the workbench.

System Requirements and limitations

• Eclipse Java development tools (JDT).
• ANTLR IDE- JDT Integration Plug-in.
• This feature is only available for Java grammars (language=Java).

ANTLR Breakpoints

• Location Breakpoint: this kind of breakpoint allow you to suspend the execution at one specific location. Parser rules only support location breakpoints
• LT Breakpoint: this kind of breakpoint allow you to suspend the execution before the parser consume a token. Usually used with lexer rules
• Consume Breakpoint: this kind of breakpoint allow you to suspend the execution after the parser consume a token. Usually used with lexer rules

1. Double click in Expr.g file to open it with the ANTLR editor.
2. Select the "INT" rule inside the "atom" rule. Right click on the rule an select ANTLR Breakpoints. Note that you can not add breakpoints by double click.



3. The "ANTLR Breakpoints" dialog show information about the selected element. In the breakpoint type list select LT and click OK.



4. The breakpoints are displayed in the vertical rule. To remove a breakpoint you need to open Breakpoints view and remove it from there.



5. Select Interpreter page
6. Select the "prog" rule in the Rule Panel
7. Select the "simpleTest" test case in the Test Panel
8. Select the "Debug (Java)" button



The "Run (Java)"/"Debug (Java)" button are available for saved test case

You can only run/debug combined/parser grammars

9. In the Confirm Perspective Switch dialog click Yes.



10. The ANTLR debug perspective.



11. Let's take a look at each view.
12. The Debug view.



This view show the rule invocation stack to the current breakpoint. You can click on any element to follow the invocation path to the current breakpoint.

13. The ANTLR Debug Events view.



This view show the debug events generated by ANTLR. The first event (LT INT 1:0 "3") is the last event generated by ANTLR, here you can see the next token ("3") to be consumed by ANTLR.

14. The ANTLR Debug Tree view.



This view show a tree representation of the rules matched by ANTLR.

15. The ANTLR Debug Input view.



This view show the current input consumed by ANTLR. At this point there is any token consumed yet. Click on the resume button on the Debug view.



Now you can see the previous token "3" already consumed by ANTLR and in the ANTLR Debug Events view you can see the next token ("6") before be consumed by ANTLR.

16. Click on the resume button on the Debug view to resume the program.
17. The text "9" is displayed in the Console view.