As for the string literal,

{
   use strict;
   use warnings;

   sub dequote_single {
      for (my $s = @_ ? $_[0] : $_) {
         s/^'//;
         s/'$//;
         s{\\([\\'])}{$1}gs;
         return STR_LIT => $_;
      }
   }

   sub dequote_double {
      for (my $s = @_ ? $_[0] : $_) {
         ...
         if (@pieces) {
            return $pieces[0];
         } else {
            return CONCAT => \@pieces;
         }
      }
   }
}

STR_LIT: /'(?:\\.|[^\\'])*'/s  { [ dequote_single($item[1]) ] }
       | /"(?:...)*'/s         { [ dequote_double($item[1]) ] }
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(assuming Perl-like literals)