clause.Expression = expr
				return
			}
		}

		clause.Expression = s.Expression
	} else {
		clause.Expression = s
	}
}

// CommaExpression represents a group of expressions separated by commas.
type CommaExpression struct {
	Exprs []Expression
}

func (comma CommaExpression) Build(builder Builder) {
	for idx, expr := range comma.Exprs {
		if idx > 0 {
			_, _ = builder.WriteString(", ")
		}

      if (!skipCommasAndWhitespace() && !exhausted()) return // Expected ',' or EOF.
    }
    result.add(Challenge(schemeName, parameters))
  }
}

/** Returns true if any commas were skipped. */
private fun Buffer.skipCommasAndWhitespace(): Boolean {
  var commaFound = false
  loop@ while (!exhausted()) {
    when (this[0]) {
      ','.code.toByte() -> {
        // Consume ','.

func ExampleScanner_emptyFinalToken() {
	// Comma-separated list; last entry is empty.
	const input = "1,2,3,4,"
	scanner := bufio.NewScanner(strings.NewReader(input))
	// Define a split function that separates on commas.
	onComma := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
		for i := 0; i < len(data); i++ {
			if data[i] == ',' {
				return i + 1, data[:i], nil
			}
		}
		if !atEOF {