stanfordnlp/CoreNLP · error · ParserException

Expected right paren!

Error message

Expected right paren!

What it means

readRightBracket throws ParserException("Expected right paren!") when, while parsing a serialized SemanticGraph, the character after a node/relation entry is not a closing bracket (')' or ']'). The serialized string is structurally incomplete or malformed.

Solutions

1. Verify the serialized string is complete and balanced (count brackets) before parsing
2. Round-trip test: only parse strings produced by the same parser version's toString()
3. Read the entire serialized graph (not line-by-line) before handing it to the parser
4. Catch ParserException and log the offending string for diagnosis

Example fix

// before
SemanticGraph sg = SemanticGraph.valueOf(line); // line truncated
// after
String full = fullGraphText.toString(); // accumulate complete text first
if (full.chars().filter(c -> c == '(').count() != full.chars().filter(c -> c == ')').count()) {
  throw new IllegalArgumentException("Unbalanced brackets");
}
SemanticGraph sg = SemanticGraph.valueOf(full);

if (s.chars().filter(c -> c=='(').count() == s.chars().filter(c -> c==')').count() && s.trim().endsWith(")")) { SemanticGraph sg = SemanticGraph.valueOf(s); }

try { sg = SemanticGraph.valueOf(s); } catch (ParserException e) { log.warn("Truncated graph text", e); }

When it happens

Trigger: Deserializing a SemanticGraph from text where an entry is truncated mid-way, a bracket was stripped, or two graphs/lines were concatenated incorrectly.

Common situations: Line-based readers cutting a multi-line serialized graph in half; manual editing of .ser/text graph dumps; regex preprocessing that removed closing parens.

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

• Expected left paren!
• Bad number put into wordToNumber. Word is: \"" + input +…
• Error in wordToNumber function.
• Bad number put into wordToNumber. Word is: \"" + curPart +…
• Doesn't do k best yet

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/8abb2153a31c7e27. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/semgraph/SemanticGraph.java:2025

      while (indexesUsed.containsKey(i))
        i++;
      return i;
    }

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

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

    private void readRelnSeparator() {
      readWhiteSpace();
      if (isRelnSeparator(peek()))
        read();
    }

    private static boolean isLeftBracket(char ch) {
      return ch == '[';
    }

    private static boolean isRightBracket(char ch) {
      return ch == ']';
    }

    private static boolean isRelnSeparator(char ch) {
      return ch == '>';

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