#!/usr/bin/perl -w
use strict;
use diagnostics;

# Mappings between character sets
my %M_2_UTF8   = ( 'A' => 'X', );          # default set
my %Ma_2_UTF8  = ( 'A' => 'a', );          # set a

my $CURRENTSET = \%M_2_UTF8; 
my @setqueue = ();                         # a stack where we push and pop


# ESC-sequences
my $switch_to_set_a = "\x1Ba";
my $reset           = "\x1Bs";             # return to previous charset

my %ESC = ( $switch_to_set_a => sub {
                            push(@setqueue, $CURRENTSET);
                            $CURRENTSET = \%Ma_2_UTF8;
                            return '';
                            },
           
            $reset          => sub {
                            $CURRENTSET = pop @setqueue;
                            return '';
                            },
           );



my $str     = 'X|a|X';
my $esc_str = qq(A|${switch_to_set_a}A|${reset}A);
my $convstr = fix($esc_str);

if ($str eq $convstr) {
    print "ok\n";
}
else {
    print "didn't work...\n";
}


sub fix {
    my $s = shift;
    
    $s =~ s{(\x1B[abcs])|(.)}       
           {repl($&)}ge;

    return $s;
}

sub repl {
    my $match = shift;
    if (exists $ESC{$match}) {
        return $ESC{$match}();
    }
    elsif (exists $CURRENTSET->{$match}) {
        return $CURRENTSET->{$match};
    }
    else {
        return $match;
    }
}
__END__