#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $data='{key1={key11=value11} | key2 = value2 | key3 = {key31=value31 | key32 = value32 | key33 = {key331=value331|key332={key3321=value3321|key3322=value3322|key3321=value3322}|key333=value333|key334=value334}}}';

package BNF;
sub encode($)
{
 my $data=shift(@_);
 my $rcu;
 $rcu=sub
 {
  my $ref;
  if($data=~s/^\s*\{//s)
  {
   $ref={};
   while(index($data,'}')!=0)
   {
    $data=~s/^[\|\s]*(.+?)\s*=//s;
    my $n=$1;
    $ref->{$n}=$rcu->();
   }
   $data=~s/^}//;
  }
  else
  {
   $data=~s/^\s*(.+?)\s*(\||\})/$2/s;
   $ref=$1;
  }
  return $ref;
 };
 return $rcu->();
}
package main;

print Dumper(BNF::encode($data))."\n";