stanfordnlp/CoreNLP · error · ParserException

Expected right paren!

Error message

Expected right paren!

What it means

StringParsingTask.readRightParen consumes whitespace and expects the next character to be a closing parenthesis ')'. If it is not, ParserException('Expected right paren!') is thrown, meaning the encoded expression ended or deviated before the closing paren was found.

Solutions

1. Check the input string for balanced parentheses and completeness
2. Print/log the string being parsed and inspect the position where parsing fails
3. Regenerate the value using the library's encoder/toString method

Example fix

// before
String input = "(a,b"; // truncated
// after
String input = "(a,b)";

String t = input.trim();
if (!t.endsWith(")")) throw new IllegalArgumentException("Encoded value must end with ')': " + input);

try {
  task.parse();
} catch (ParserException e) {
  log.error("Malformed encoded value '" + input + "': " + e.getMessage());
}

When it happens

Trigger: Parsing an encoded string where after reading the inner elements the next character is not ')', e.g. truncated input like '(a,b', extra tokens inside the parens, or a wrong closing character.

Common situations: Truncated files or cut-and-paste that dropped the final character; strings built manually with unbalanced parentheses; mixing encodings produced by different writers.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• invalid format: ||
• Dependencies should be for the format 'type(arg-idx…
• Expected left paren!
• Unclosed paren in encoded array: " + encoded
• Tag did not start with <

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/868afc0087d1fdc3. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/StringParsingTask.java:98

    return sb.toString().intern();
  }

  // .....................................................................

  protected void readLeftParen() {
    // System.out.println("Read left.");
    readWhiteSpace();
    char ch = read();
    if (!isLeftParen(ch))
      throw new ParserException("Expected left paren!");
  }

  protected void readRightParen() {
    // System.out.println("Read right.");
    readWhiteSpace();
    char ch = read();
    if (!isRightParen(ch)) 
      throw new ParserException("Expected right paren!");
  }

  protected void readDot() {
    readWhiteSpace();
    if (isDot(peek())) read();
  }

  protected void readWhiteSpace() {
    char ch = read();
    while (isWhiteSpace(ch) && !isEOF()) {
      ch = read();
    }
    unread();
  }

  // .....................................................................

  protected char read() {

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