my @new_song = map { $_ = $_ =~ /^[a-g]$/ ? $notes{$_} : 'not a note'; $_ } @song_notes;

##</code><code>##

my @new_song = map { /^[a-g]$/ ? $notes{$_} : 'not a note' } @song_notes;

##</code><code>##

my @new_song = map { $_ = $$SoM{$_} ? $_.' '.$$SoM{$_} : 'not a note'; $_ } @$notes;

##</code><code>##

my @new_song = map { $_ = $SoM->{$_} ? $_ . ' ' . $SoM->{$_} : 'not a note' } @$notes;