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my %code = do { my $i = 0; map { $_ => $i++ } split /,/, $tokens };

my %code = sub { map { $_[$_] => $_ } 0..$#_ }->( split /,/, $tokens )
+;

my $i = 0;
my %code = map { $_ => $i++ } split /,/, $tokens;

my @code = split /,/, $tokens;
my %code = map { $code[$_] => $_ } 0..$#code;