Debugging a look-ahead

Top  Previous  Next

Examples > Java > Debugging a look-ahead


You can see what happens in detail when a look-ahead is tested, if you step into the look-ahead with the debugger. First you can put a breakpoint on the word "System" in the sixth line of the example text.





The project then can be run up to this point. After another three single steps the "IF" is marked in the production "BlockStatement".







Now can step into the look-ahead. After a click on the corresponding button the debugger changes to the production "LocalVariableDeclaration" and a '1' is shown in the little field right next to the button.




This means that the debugger is in the first level of a look-ahead now. This is indicated by a '1' with a gray background in front of the name of the production at the top of the stack in the window for the stack too.




The debugger can be executed just the same as used for the main parser now within the look-ahead. Behind the word "println", however, the parser cannot continue: no following token is recognized. The look-ahead has failed and is left. The debugger again is in the production "BlockStatement" now but in the ELSE-branch of the IF-structure.





The field for the indication of the level of the look-ahead is empty, i.e. the debugger shows the progress in the main parser again.






This page belongs to the TextTransformer Documentation

Home  Content  German