RosettaCodeData/Task/Factorial/Lang/factorial-2.lang

fp.fact = ($n) -> {
	if($n < 0) {
		throw fn.withErrorMessage($LANG_ERROR_INVALID_ARGUMENTS, n must be >= 0)
	}elif($n < 2) {
		return 1L
	}
	
	return parser.op($n * fp.fact(-|$n))
}