Handling errors in ANTLR4 JavaScript - Stack Overflow

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I am using ANTLR4 JavaScript to create a sort of a web IDE for a custom language.

It all works great, apart from the fact that errors are logged to the console and I can't figure out a way to redirect those errors somewhere I can present them to the users.

At the moment, they are shown on the JS console like this:

Could anyone point me on the right direction (which file I need to edit, etc)?

I am using ANTLR4 JavaScript to create a sort of a web IDE for a custom language.

It all works great, apart from the fact that errors are logged to the console and I can't figure out a way to redirect those errors somewhere I can present them to the users.

At the moment, they are shown on the JS console like this:

Could anyone point me on the right direction (which file I need to edit, etc)?

• javascript
• error-handling
• antlr4

Share Improve this question Follow edited Feb 19, 2021 at 20:08 ggorlen 57.4k88 gold badges111111 silver badges154154 bronze badges asked May 16, 2015 at 13:07 EduAlmEduAlm 81333 gold badges1111 silver badges2828 bronze badges 2

• 2 Cannot speak directly to the Javascript implementation, but for Java there are Parser.removeErrorListeners(), that removes the default ConsoleErrorListener, and Parser.addErrorListener(....), to add back your own custom error listener. Do this after creating the Parser and before running it. – GRosenberg Commented May 17, 2015 at 1:59
• @GRosenberg Thanks, that helped me figure it out! Can you post it as an answer so I can accept it? – EduAlm Commented May 17, 2015 at 18:51

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2 Answers 2

Sorted by: Reset to default 5

Cannot speak directly to the Javascript implementation, but for Java there are:

Parser.removeErrorListeners() // removes the default ConsoleErrorListener Parser.addErrorListener(....) // add back a custom error listener

Do this after creating the Parser and before running it.

You can do this by implementing the antlr4.error.ErrorListener interface and providing one of the interface methods such as syntaxError to be invoked upon each error.

class ExprErrorListener extends antlr4.error.ErrorListener {
  syntaxError(recognizer, offendingSymbol, line, column, msg, err) {
    ...
  }
}

Disable the default error listener and enable the custom listener with:

parser.removeErrorListeners();
parser.addErrorListener(new ExprErrorListener());

Note that you can skip the class and pass in an object with the syntaxError function available. Here's a minimal, plete example on the Expr.g4 grammar:

const antlr4 = require("antlr4");
const {ExprLexer} = require("./parser/ExprLexer");
const {ExprParser} = require("./parser/ExprParser");

const expression = "2 + 8 * 9 - \n";
const input = new antlr4.InputStream(expression);
const lexer = new ExprLexer(input);
const tokens = new antlr4.CommonTokenStream(lexer);

const parser = new ExprParser(tokens);
parser.buildParseTrees = true;
parser.removeErrorListeners();
parser.addErrorListener({
  syntaxError: (recognizer, offendingSymbol, line, column, msg, err) => {
    console.error(`${offendingSymbol} line ${line}, col ${column}: ${msg}`);
  }
});

const tree = parser.prog();

Gives:

[@6,12:12='\n',<10>,1:12] line 1, col 12: mismatched input '\n' expecting {'(', ID, INT}

See also error handlers.

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