using System;

//abc
static void Match_ABC(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    const string pattern = @"abc";
    if(input[0..3].SequenceEqual(pattern))
    {
        ptr += 3;
        region_end = ptr;
    }
}

//a[abc]d
static void Match_A_charset_ABC_C(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    if(input[0] == 'a' && (input[1] == 'a' || input[1] == 'b' || input[1] == 'c') && input[2] == 'd')
    {
        ptr += 3;
        region_end = ptr;
    }
}

//[abc]
static void Match_charset_ABC(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    if(input[0] == 'a' || input[0] == 'b' || input[0] == 'c')
    {
        ptr += 1;
        region_end = ptr;
    }
}

//.
static void Match_Dot(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

        ptr += 1;
        region_end = ptr;
}