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Structural recursion on setsHi, I am not sure I am entirely happy with the usual structural recursion on sets approaches. They all look like a bit of cheating, i.e. using lists under covers, broadly speaking. I mean SRI/SRU/powerset/etc tricks (http://citeseer.ist.psu.edu/722866.html). E.g. in the SRI method (collection insertion representation), we can do matching using the insertion operator that 'disassembles' a nonempty set thereby maing it amenable to something like foldr. On the other hand, the 'choose' operator is criticised (elsewhere) as 'nondeterministic'. I am aware of various laws and such that make SRI 'work', I just have a feeling that the insertion operator is a kind of deus ex machina as much as 'choose' is ! Please comment. Thanks. By vc at 20080229 18:10  LtU Forum  previous forum topic  next forum topic  other blogs  3596 reads

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