use 5.010;  # re features
use strict;
use warnings;

#for ('abcdef') {
#   m{
#      (?(DEFINE)
#         (?<x>
#            ( . ) ( . )
#            (?{ '...' })
#         )
#         (?<y>
#            ( . ) ( . )
#            (?{ print("(???,$^N)") })
#         )
#         (?<z>
#            ( . ) ( . )
#            (?{ '...' })
#         )
#      )
#
#      (?&y)+
#   }x;
#}

print "(a,b)(c,d)(e,f)";
print("\n");