What causes "Invalid node pattern class: for variable " in stanfordnlp/CoreNLP?

Bind the variable to a single node pattern (e.g. a NodePattern or NodePatternExpr), or use a literal node expression at the reference site

stanfordnlp/CoreNLP · error · java.lang.Error

Invalid node pattern class: for variable

Error message

Invalid node pattern class:  for variable

What it means

Env.getNodePattern resolves a variable to a NodePattern; if the bound object is a SequencePattern whose pattern expression is not a simple NodePatternExpr (e.g. a sequence or composite expression), it cannot be used as a node pattern and throws an Error (not Exception).

Solutions

Bind the variable to a single node pattern (e.g. a NodePattern or NodePatternExpr), or use a literal node expression at the reference site
If a sequence is intended, use it in sequence position with getSequencePatternExpr semantics, not as a node
Split the sequence into separate node variables

Defensive patterns

Strategy: type-guard

Validate before calling

Object obj = env.get(name);
if (obj instanceof SequencePattern && !(((SequencePattern) obj).getPatternExpr() instanceof SequencePattern.NodePatternExpr)) {
  throw new IllegalStateException(name + " is a sequence pattern; use it in sequence position, not as a node");
}

Type guard

boolean isNodePatternUsable(Object o) { return o instanceof NodePattern || o instanceof SequencePattern.NodePatternExpr || (o instanceof SequencePattern s && s.getPatternExpr() instanceof SequencePattern.NodePatternExpr); }

Try / catch

try { NodePattern np = env.getNodePattern(name); } catch (Error e) { log.error("Variable {} is not a node pattern: {}", name, e.getMessage()); throw e; }

Prevention

Use distinct variable naming conventions for node vs sequence variables
Check the bound expression type when binding, not at lookup time
Only reference single-token expressions in node position

When it happens

Trigger: Referencing, in node position (e.g. [$VAR] inside a rule node), a variable bound to a full sequence pattern rather than a single node pattern.

Common situations: Binding a variable to a multi-token sequence and then using it as a single token pattern in a rule; confusing sequence variables with node variables.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/8622cdf18d4e60c8. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ling/tokensregex/Env.java:335

  }

  public void bind(String name, SequencePattern pattern) {
    bind(name, pattern.getPatternExpr());
  }

  public void unbind(String name) {
    bind(name, null);
  }

  public NodePattern getNodePattern(String name) {
    Object obj = variables.get(name);
    if (obj != null) {
      if (obj instanceof SequencePattern) {
        SequencePattern seqPattern = (SequencePattern) obj;
        if (seqPattern.getPatternExpr() instanceof SequencePattern.NodePatternExpr) {
          return ((SequencePattern.NodePatternExpr) seqPattern.getPatternExpr()).nodePattern;
        } else {
          throw new Error("Invalid node pattern class: " + seqPattern.getPatternExpr().getClass() + " for variable " + name);
        }
      } else if (obj instanceof SequencePattern.NodePatternExpr) {
        SequencePattern.NodePatternExpr pe = (SequencePattern.NodePatternExpr) obj;
        return pe.nodePattern;
      } else if (obj instanceof NodePattern) {
        return (NodePattern) obj;
      } else if (obj instanceof String) {
        try {
          SequencePattern.NodePatternExpr pe = (SequencePattern.NodePatternExpr) parser.parseNode(this, (String) obj);
          return pe.nodePattern;
        } catch (Exception pex) {
          throw new RuntimeException("Error parsing " + obj + " to node pattern", pex);
        }
      } else {
        throw new Error("Invalid node pattern variable class: " + obj.getClass() + " for variable " + name);
      }
    }
    return null;

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