CODEWITHSUNDEEP
javaantlr4
GMCS Pune
GMCS Pune

Reputation: 83

ANTLR 4 Error and Exception handling in advance before triggering listener events

In ANTLR 4 error/exception handling can be extended by implementing ANTLRErrorListener. It's events will be fired only when I traverse tree which is created using lexer and parser. e.g.

parser.removeErrorListeners();
parser.addErrorListener(new MyTryDSLErrorListener());
ParseTreeWalker walker = new ParseTreeWalker();
MyTryDSLListener listener = new MyTryDSLListener(); // Can be replaced by default Base listener(empty implementation)
walker.walk(listener, parser.test()); // At this line tree will be traversed and if any error then MyTryDSLErrorListener's callback will be called.

I want to know if is there any clean way to get errors from input string without invoking listener/visitor.

NOTE: Though there is a way to handle this by replacing listener with default implementations. And then again traverse tree with own implemented listeners, like as below:

walker.walk(new TryDSLBaseListener(), parser.test()); // Find if has any errors.
walker.walk(new MyTryDSLListener(), parser.test()); // Actual use case.

Upvotes: 0

Views: 2302

Answers (1)

GRosenberg
GRosenberg

Reputation: 6001

The ANTLRErrorListener only reports errors encountered by the Parser in-line during parsing. That is, the listener reports syntax errors encountered as a result of the Parser's execution of a grammar's start rule.

The listener has no participation with parse-tree walk operations.

Update

parser.removeErrorListeners();
parser.addErrorListener(new MyTryDSLErrorListener());
ParseTree tree = parser.test();

Calling parser.test() initiates parser execution to create the parse tree. During execution, if and as the parser encounters an error, the parser reports the error through the ANTLRErrorListeners registered with the parser. All such errors will have been reported when parser.test() returns.

At this point a parse tree has been constructed. Walking is entirely separate from tree construction. The parser registered ANTLRErrorListeners will not be called. 

ParseTreeWalker walker = new ParseTreeWalker();
MyTryDSLListener listener = new MyTryDSLListener();
walker.walk(listener, tree);

Upvotes: 1

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