using System;
using System.IO;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var line = "[A] == [B] * 10 - FUNCTION{[C], STRING_EXPRESSION, FUNCTION{[D],[C],[E]}}, FUNCTION{[C], [X]}, 100";
        var matches = Regex.Matches(line, @"(?:(?:\{(?>[^{}]+|{(?<n>)|}(?<-n>))*(?(n)(?!))})|[^,])+");
        foreach (Match m in matches)
        	Console.WriteLine(m.Value.Trim());
        
	}
}