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On 6/26/06, Andre van Tonder <andre@xxxxxxxxxxxxxxxxx> wrote:
I like the operational semantics in the SRFI, since it may be less ambiguous than the alternative declarative approach. As corrobrating evidence, I can mention the syntax-case implementation in SRFI-72. That implementation satisfies declarative descriptions of hygiene. However, the implementation technique is based on an "implicitized" version of explicit renaming, not marking/substitution. There are some highly obscure corner cases where it behaves differently from the marking algorithm, while still satisfying hygiene. I have to recheck, but I think these ambiguities should be resolved by specifying the algorithm as is done here (though perhaps a little more detail might be required).
I think the trick is to make an unambiguous declarative specification. David