How to use the postcss-values-parser.func function in postcss-values-parser

// hex is the node value
	const hex = node.value;

	// conditionally expand a hex
	const hex8 = `0x${hex.length === 5 ? hex.slice(1).replace(/[0-9A-f]/g, '$&$&') : hex.slice(1)}`;

	// extract the red, blue, green, and alpha values from the hex
	const [r, g, b, a] = [
		parseInt(hex8.slice(2, 4), 16),
		parseInt(hex8.slice(4, 6), 16),
		parseInt(hex8.slice(6, 8), 16),
		Math.round(parseInt(hex8.slice(8, 10), 16) / 255 * alphaDecimalPrecision) / alphaDecimalPrecision
	];

	// return a new rgba function, preserving the whitespace of the original node
	const rgbaFunc = valueParser.func({ value: 'rgba', raws: Object.assign({}, node.raws) });

	rgbaFunc.append(valueParser.paren({ value: '(' }));
	rgbaFunc.append(valueParser.number({ value: r }));
	rgbaFunc.append(valueParser.comma({ value: ',' }));
	rgbaFunc.append(valueParser.number({ value: g }));
	rgbaFunc.append(valueParser.comma({ value: ',' }));
	rgbaFunc.append(valueParser.number({ value: b }));
	rgbaFunc.append(valueParser.comma({ value: ',' }));
	rgbaFunc.append(valueParser.number({ value: a }));
	rgbaFunc.append(valueParser.paren({ value: ')' }));

	return rgbaFunc;
};