Re: [q-lang-users] Multiple supertypes for Q?

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> Multiple supertypes would seem to be fairly cheap and easy to add to Q.

Useful? Yes. Easy to add? No. The problem is not so much the runtime 
costs, but that the current algorithm which generates the pattern 
matching automaton (the hairiest part of the bytecode compiler), only 
works with single inheritance.

It's probably possible to extend the algorithm to support multiple 
inheritance, but I don't think it's trivial. (If anyone wants to take a 
look at this, the basic term acceptor technique is described in my paper 
in the "Rewriting Techniques and Applications" 1991 proceedings (LNCS 
488). The source code is in qcrules.c.)

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag