Chapter 4

hash variables
anonymous hashes for nested structure (AoH)
regex with named captures
named capture variables
list manipulation with map
smartmatch ~~
ranges (..) using ^

$/[0] $()/[0] $0
style for first,  last easy to overlook

$/ aka $

    when /^ r \s* (<digit>)/    { splice @note, $/[0], 1 if 0 <= $/[0] < +@note }
    when /^ r \s* <digit>+/   { splice @note, $/<[0], 1 if 0 <= $/[0] < +@note }

my token pos { \d+ }