apple/pkl · error · GenericParserError

unexpectedTokenForExpression

unexpectedTokenForExpression

Error message

Unexpected token `{0}`.

What it means

The parser found a token that cannot appear in expression position and no specific expectation was set, so it throws the generic 'Unexpected token' message naming the token. This is the fallback expression syntax error in parseExpr.

Source

Thrown at pkl-parser/src/main/java/org/pkl/parser/GenericParserImpl.java:908

            ff(children);
            children.add(parseExpr());
            yield new Node(NodeType.LET_EXPR, children);
          }
          case TRUE, FALSE -> new Node(NodeType.BOOL_LITERAL_EXPR, next().span);
          case INT, HEX, BIN, OCT -> new Node(NodeType.INT_LITERAL_EXPR, next().span);
          case FLOAT -> new Node(NodeType.FLOAT_LITERAL_EXPR, next().span);
          case STRING_START -> parseSingleLineStringLiteralExpr();
          case STRING_MULTI_START -> parseMultiLineStringLiteralExpr();
          case IDENTIFIER -> parseUnqualifiedAccessExpr();
          case EOF ->
              throw parserError(
                  ErrorMessages.create("unexpectedEndOfFile"), prev().span.stopSpan());
          default -> {
            var text = _lookahead.text(lexer);
            if (expectation != null) {
              throw parserError("unexpectedToken", text, expectation);
            }
            throw parserError("unexpectedTokenForExpression", text);
          }
        };
    return parseExprRest(expr);
  }

  @SuppressWarnings("DuplicatedCode")
  private Node parseExprRest(Node expr) {
    // amends
    if (lookahead() == Token.LBRACE) {
      var children = new ArrayList<Node>();
      children.add(expr);
      ff(children);
      if (expr.type == NodeType.PARENTHESIZED_EXPR
          || expr.type == NodeType.AMENDS_EXPR
          || expr.type == NodeType.NEW_EXPR) {
        children.add(parseObjectBody());
        return parseExprRest(new Node(NodeType.AMENDS_EXPR, children));
      }

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Delete or correct the unexpected token at the reported span
2. Look slightly earlier in the file for a missing operand or bracket that displaced the token
3. Reformat with a Pkl formatter to expose structural mistakes

Example fix

// before
x = , y = 2
// after
x = 1
y = 2

try { parser.parse(src) } catch (e) {
  if (/^Unexpected token/.test(String(e.message)) && !/Expected/.test(String(e.message))) {
    // generic expression-position syntax error: show span context
  }
  throw e;
}

When it happens

Trigger: parseExpr's default branch when `expectation == null` and `_lookahead` is not a valid expression-start token — e.g. a stray `}` `,` `:` or operator at top level.

Common situations: Dangling comma or colon from an edit; an operator without a left operand; keywords like `then`/`else` appearing outside their construct; mismatched brackets shifting everything into expression position.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• ErrorMessages.create(errorKey, args)
• unexpectedToken
• missingDelimiter
• unexpectedEndOfFile
• stringContentMustBeginOnNewLine

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/ba82e8152aad55e6. Report an issue: GitHub.