Re: [gnugo-devel] dfa_unsort_1_25.1

[Inge Wallin]

> Inge wrote:
> > A long time ago, I proposed a keyword 'supercedes' for patterns.
> > Consider the two patterns above (never mind pattern syntax here):
> 
> Then you must have called it something different, because I have
> nothing like that in my mail archive.

Very possible, maybe even likely.  I don't remember any details.

> > Pattern C1
> > 
> > XX
> > ..
> > XX
> >  
> > :supercedes(C2)
> > 
> > Pattern C2
> > 
> > X
> > .
> > X
> > 
> > This would mean that pattern C2 would never even be tried if C1
> > matches.  I think that we could easily gain a lot of nodes here since
> > we could easily create special case patterns for common, but expensive
> > reading cases.
> 
> Anyway, this seems rather unmanageable to me. 

Not unlikely.  I thought so myself and never tried to implement it.

> Also we already have a
> cutoff in that the constraint of C2 won't be evaluated if the two
> strings already have been amalgamated, e.g. by pattern C1.

True, but that wasn't the point.  This construct should be useful in
all pattern databases, including the owl patterns.  It could save many
reading nodes in situation that are complex in general but where there
exists a common special case that can be found with a much cheaper
constraint or maybe no constraint at all.  In that case the complex
constaint wouldn't be evaluated at all.

        -Inge