stanfordnlp/CoreNLP · error · IllegalArgumentException

Coreference is not implemented for French

Error message

Coreference is not implemented for French

What it means

Stanford CoreNLP's FrenchDocument overrides the pipeline annotator hooks but does not implement coreference resolution for French, so Document.coref() throws IllegalArgumentException immediately. The library uses language-specific Document subclasses and only English (and a few others) ship coreference models. This is an explicit unsupported-operation guard, not a bug.

Solutions

1. Remove the coref annotator from the pipeline / skip Document.coref() for French text
2. Run coreference with the English pipeline only if your data is English
3. Use an external French-capable coreference tool (e.g. a neural coref model supporting French) and feed its output into your app
4. Wrap coref() in a feature check and degrade gracefully when unsupported

Example fix

// before
Document doc = new Document("...");
Map<Integer, CorefChain> chains = doc.coref();
// after
if (doc instanceof FrenchDocument) {
  System.err.println("coref not supported for French");
} else {
  Map<Integer, CorefChain> chains = doc.coref();
}

if (doc instanceof FrenchDocument) {
  throw new UnsupportedOperationException("coref not supported for French");
}

boolean supportsCoref(Document d) {
  return !(d instanceof FrenchDocument);
}

try {
  Map<Integer, CorefChain> chains = doc.coref(props);
} catch (IllegalArgumentException e) {
  if (e.getMessage().contains("not implemented")) {
    chains = Collections.emptyMap();
  } else { throw e; }
}

When it happens

Trigger: Calling CorefChain coref(Properties) or any Document/Sentence-level API that triggers coreference (e.g. Document.coref(), Sentence.coref(), or running an annotator pipeline with the 'coref' annotator on a French document).

Common situations: Using StanfordCoreNLP with the coref annotator and -language fr; porting an English coref pipeline to French; assuming all languages supported by the simple API support all annotators.

Related errors

• Coreference is not implemented for German
• allSentences != allWords
• Cannot have these two ordering constraints
• Cannot have these two ordering constraints
• Coreference is not implemented for Arabic

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/b77be8ca0be951a9. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/simple/FrenchDocument.java:88

  /**
   * No lemma annotator for French -- set the lemma to be the word.
   *
   * @see Document#runLemma(Properties)
   */
  @Override
  protected Document runLemma(Properties props) {
    return mockLemma(props);
  }


  @Override
  protected Document runSentiment(Properties props) {
    throw new IllegalArgumentException("Sentiment analysis is not implemented for French");
  }

  @Override
  public Map<Integer, CorefChain> coref(Properties props) {
    throw new IllegalArgumentException("Coreference is not implemented for French");
  }

}

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