On 10/4/07, Jules Bean
...and indeed it can't be done, except by the naive brute-force method of comparing every subtree, possibly optimised by cryptographically hashing a representation of every subtree, since sharing isn't an observable property.
At least one Prolog implementation (I forget which, I'm sorry), had a [de]serialisation library which used a hash-consing approach. Basically, it did its serialization using a post-order traversal and emitted references to previous values when the same value had already been emitted. Not rocket science. Actually, I've heard a Prolog guy - Bart Demoen - talk about doing pretty much this during GC to improve sharing. cheers, T. -- Thomas Conway drtomc@gmail.com Silence is the perfectest herald of joy: I were but little happy, if I could say how much.