in src/main.rs [171:181]
fn index_to_row_col(s: &str, index: usize) -> (usize, usize) {
let chunk = &s[..index];
let line_num = chunk.chars().filter(|x| x == &'\n').count();
let last_newline = if let Some(result) = chunk.rfind('\n') {
result as isize
} else {
-1
};
let col = index as isize - last_newline - 1;
(line_num, col as usize)
}