stanfordnlp/CoreNLP · error · Error

Unknown sequence pattern variable

Error message

Unknown sequence pattern variable 

What it means

A plain java.lang.Error thrown by the grammar's sequence-variable production when a REGEXVAR token references a name not registered in the parsing Env (env.getSequencePatternExpr(name, true) returns null). Variables must be defined in the environment (via Env setResult/ bind) before they can be referenced in a pattern. It is thrown as an Error, not a ParseException.

Solutions

1. Define the variable before use, either with env.bind(name, value) or by loading the rule file that defines it first.
2. Check the variable name spelling and case against the definition in the rules file.
3. Load all dependent rule files into the same Env in dependency order.
4. Pre-validate by calling env.getSequencePatternExpr(name, false) yourself and reporting missing names with a friendly message.

Example fix

// before
SequencePattern<CoreMap> p = SequencePattern.compile(env, "$DATE"); // Error: Unknown sequence pattern variable $DATE
// after
env.bind("$DATE", SequencePattern.compile(env, "[ { ner:DATE } ]+"));
SequencePattern<CoreMap> p = SequencePattern.compile(env, "$DATE");

// Pre-check: every $VAR referenced must be defined in the Env
static void checkVarsDefined(Env env, String pattern) {
  java.util.regex.Matcher m = java.util.regex.Pattern.compile("\\$[A-Za-z_][A-Za-z0-9_]*").matcher(pattern);
  while (m.find()) {
    if (env.getSequencePatternExpr(m.group(), false) == null)
      throw new IllegalArgumentException("Undefined variable in pattern: " + m.group());
  }
}

try {
  SequencePattern<CoreMap> p = SequencePattern.compile(env, pattern);
} catch (Error e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Unknown sequence pattern variable")) {
    throw new IllegalArgumentException("Define the variable with env.bind() before compiling: " + pattern, e);
  }
  throw e;
}

When it happens

Trigger: Parsing a sequence pattern containing $VAR (REGEXVAR) where $VAR was never bound in the Env, e.g. SequencePattern.compile(env, "$MYVAR") without env.bind or a prior rule defining MYVAR.

Common situations: Rules files referencing variables defined in other files that were not loaded; typos in variable names ($Date vs $DATE); loading a rule file out of order so the variable definition rule hasn't run yet.

Related errors

• Unknown sequence pattern variable
• Attribute match already defined
• Attribute already defined
• Field already defined:
• Attribute match already defined:

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/96f2b992eda891f7. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ling/tokensregex/parser/TokenSequenceParser.jj:797

    |
    "["
    (  node = NodeDisjConj(env)  )
    "]"
  )
  { return node; }

}

SequencePattern.PatternExpr SeqVar(Env env) : {
  SequencePattern.PatternExpr expr;
  Token name;
} {
  (
    name = <REGEXVAR>
    {
        expr = env.getSequencePatternExpr(name.image, true);
        if (expr == null) {
            throw new Error("Unknown sequence pattern variable " + name.image);
        }
    }
  )
  { return expr; }

}

SequencePattern.PatternExpr SeqBackRef(Env env) : {
  Token name;
} {
    name = <BACKREF>
    {
        int v = Integer.parseInt(name.image.substring(1));
        return new SequencePattern.BackRefPatternExpr(CoreMapNodePattern.TEXT_ATTR_EQUAL_CHECKER, v);
    }
}

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