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%nodes=( root => { parents => [],
                   probs => [0.01]}, # P(root)
...
                   probs => [0.12,0.24,   # P(other|!root,!some), P(ot
+her|!root,some)
                             0.81,0.18]}, # P(other|root,!some), P(oth
+er|root,some)
         );

# the state you start from
%state=(root=>1,some=>0);
...
 $i=($i<<2)+$state{$_} # this is a simple encoding. Just use the same 
+for updating and accessing
}
$prob=$nodes{other}{probs}[$i];

use XML::Simple;
print XMLout(\%nodes);