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CheckToken

procedure CheckToken(T: Char);

Example​

procedure RequireIdentifier(Parser: TParser);
begin
  if Parser = nil then Exit;

  Parser.CheckToken(toSymbol);
  // The current token is unchanged; read it before advancing.
end;

Usage​

CheckToken requires the current parser token to have one exact character code and raises a token-specific parser error when it does not.

Additional Technical Info​

CheckToken compares T with the current Token. A match returns without changing parser state. A mismatch raises EParserError; it does not search ahead, consume input or recover.

The generated message depends on the requested code. toSymbol reports that an identifier was expected; toString and the native toWString code report a string; toInteger and toFloat report a number. Other values report the literal expected character. Delphi then appends the current SourceLine through the common parser-error formatter.

Use this method before a type-specific getter when the grammar requires an exact kind:

  • Check toSymbol before TokenComponentIdent.
  • Check toInteger before TokenInt.
  • Check toFloat before TokenFloat, or accept both integer and float deliberately if the grammar permits either.
  • Check literal punctuation such as '=', '(' or '}' directly.

CheckToken does not advance. Call NextToken explicitly after consuming the value. Repeated successful checks are harmless; repeated failures continue to raise at the same token.

The constructor exposed to scripts installs no OnError callback, so the current Velox-created parser cannot suppress the exception. Handle it at the flow boundary when input can be invalid.

The example is source-reviewed only; no parser was executed.

External references

Created 2026-07-15