use strict;
use warnings;
 
 # version 0.2
 
 $\="\n";
 
 #--- flags  
 my $flag_interactive; # true => no extra escaping of backslashes
 
 
 my $RE='\w*(a|b|c)\d\(';
 $RE='\d{2,3}';
 $RE='"(.*?)"';
 
 print "Perlcode: $RE";
 
 #--- hide pairs of backslashes
 $RE=~s#\\\\#\0#g;
 
 # TODO check for suitable long "hidesequence" instead of a simple \0
 
 #--- TODO normalisation of needless escaping
 # e.g.  from /\"/ to /"/, since it's no difference in perl but might confuse elisp
 
  
 #--- toggle escaping of 'backslash constructs'
 my $bsc='(){}|';
 $RE=~s#[$bsc]#\\$&#g;  # escape them once
 $RE=~s#\\\\##g;        # and erase double-escaping
 
 
 
 #--- replace character classes
 my %charclass=(
 	    w => 'word' ,   # TODO: emacs22 already knows \w ???
 	    d => 'digit',
 	    s => 'space'
 	   );
 
 my $kc=join "|",keys %charclass;
 $RE=~s#\\($kc)#[[:$charclass{$1}:]]#g; 
 
 
 
 #--- unhide pairs of backslashes
 $RE=~s#\0#\\\\#g;
 
 #--- escaping for elisp string
 unless ($flag_interactive){
   $RE=~s#\\#\\\\#g; # ... backslashes
   $RE=~s#"#\\"#g;   # ... quotes
 }
 
 
 print "Elispcode: $RE";