Re: gnubol: subsets

[RKRayhawk@aol.com]

In a message dated 11/25/99 11:28:14 AM EST, TIMJOSLING@prodigy.net writes:

<< 
 The code can be in the reductions for a and b so there is no real problem 
with
 this (when there are two options; when there are many as in the data 
definitions,
 you need to manually count them to avoid exponential explosion)..
  >>

These ideas are exactly correct. Except, IMHO, entirely optimisitic. In the 
code base are mistakes so even though you have expectation of two conditional 
clauses, that is not what you encounter, instead you can get many. We want to 
stay on our feet. Especially when you see that there could be the kind of 
errors that make later conditionals fly back to the outer arithmetic where 
numerous can accumulate.

And this is where the seeming theory becomes a practical issue for the 
compiler writer.  Any where you have an expected count, say in the limit of 
three phrases in a VARYING clause, or just one VARYING clause in a perform; 
you could of course see something quite different. Any time you expect an 
order of clauses, you could see something quite different.

The order of the day is manual count. It is real unhappy. The optimistic 
grammar will not do it. You will loose too much code and user will complain 
that subsequent compiles discover problems you should have flagged before.

The real issue here is the kind of thinking the tools encourage. We can not 
have the nieve hierarchy of rules that we at first dream of.  Many source 
programs do not fit together!  Many people want to use the compiler for early 
code review. Even in mostly good code minor error can cause serious 
disruptions.

In the procedure division, IMHO, we will need much manual counting, and we 
will also need to review the order of occurence after the fact. Most tedius.

Best Wishes,
Bob Rayhawk
RKRayhawk@aol.com








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