# -------------------------------------------------
# 1. Basic building blocks
# -------------------------------------------------
my $hex2   = qr/[0-9A-Fa-f]{2}/;               # exactly 2 hex digits
my $hex2p  = qr/[0-9A-Fa-f]{2,}/;              # 2 or more hex digits
my $hexXp  = qr/[0-9A-Fa-fXx]{1,4}/;           # 1‑4 hex/X digits
my $hexXp8 = qr/[0-9A-Fa-fXx]{1,8}/;           # 1‑8 hex/X digits
my $opt_h  = qr/[Hh]?/;                       # optional trailing H/h
my $quotes = qr/"[^"]*"/;                     # optional quoted literal

# -------------------------------------------------
# 2. Re‑usable sub‑patterns
# -------------------------------------------------
my $int      = qr/\bINT\s?$hex2$opt_h/;       # INT <byte>
my $mem_addr = qr/\bMEM\s?$hexXp:$hexXp$opt_h/;  # MEM <addr>:<addr>
my $mem_long = qr/\bMEM\s?$hexXp8$opt_h/;     # MEM <addr>
my $port_rng = qr/\bPORT\s?$hexXp$opt_h\-$hexXp$opt_h/; # PORT <range>
my $port_one = qr/\bPORT\s?$hexXp$opt_h/;    # PORT <single>
my $hash_ref = qr/\#[0-9A-Z][0-9]{4}\b/;     # #<letter><4 digits>
my $ea_xhl   = qr/\b(?:E?A[XHL])=$hex2p$opt_h/; # EA/XHL assignment

my $reglist = qr/
    (?:E?[ABCD][XHL]|E?[SD]I|E?[SB]P|[DESC]S)=$hex2p$opt_h
/x;                                            # a single register entry

my $opt_reglist = qr/
    (?:\/$reglist)+
/x;                                            # one or more "/<reg>" entries

# -------------------------------------------------
# 3. Full pattern with named captures
# -------------------------------------------------
my $linking_re = qr/
    # 1. INT with optional register list and optional quoted literal
    (?<int_full>
        $int
        $opt_reglist?
        $quotes?
    )
    |
    # 2. INT with only optional quoted literal
    (?<int_simple>
        $int
        $quotes?
    )
    |
    # 3. EA/XHL with repeated register list and optional quoted literal
    (?<ea_xhl_full>
        $ea_xhl
        (?:\/$reglist)*
        $quotes?
    )
    |
    # 4. Hash reference (e.g. #A1234)
    (?<hash_ref>
        $hash_ref
    )
    |
    # 5. MEM range (addr:addr) with optional quoted literal
    (?<mem_range>
        $mem_addr
        $quotes?
    )
    |
    # 6. MEM single address with optional quoted literal
    (?<mem_simple>
        $mem_long
        $quotes?
    )
    |
    # 7. @&#8209;reference (addr:addr) with optional quoted literal
    (?<at_ref>
        \@$hexXp:$hexXp$opt_h
        $quotes?
    )
    |
    # 8. PORT range with optional quoted literal
    (?<port_range>
        $port_rng
        $quotes?
    )
    |
    # 9. PORT single value with optional quoted literal
    (?<port_simple>
        $port_one
        $quotes?
    )
/x;

# -------------------------------------------------
# 4. Usage example
# -------------------------------------------------
if ( $linking =~ $linking_re) {
    my %cap = %+;   # hash of all named captures
    if ( $cap{int_full} ) {
        # handle INT with register list
    }
    elsif ( $cap{mem_range} ) {
        # handle MEM range
    }
    # …other branches as needed
}