RosettaCodeData/Task/Anonymous-recursion/Lang/anonymous-recursion.lang

fp.fib = ($n) -> {
	if($n < 0) {
		throw fn.withErrorMessage($LANG_ERROR_INVALID_ARGUMENTS, n must be >= 0)
	}
	
	fp.innerFib = ($n) -> {
		if($n < 2) {
			return $n
		}
		
		return parser.op(fp.innerFib($n - 1) + fp.innerFib($n - 2))
	}
	
	return fp.innerFib($n)
}