Re: Alternative algorithm to restrict use of data/string in patterns.

[James Clark <jjc@jclark.com>]

> > Would another way to do it be to have calcFPDS just take s single
argument
> > and for group to do
> >
> > if (p is <group>p1 p2</group>) {
> >    if (isNullable(p1))
> >       return calcFPDS(p1) || calcFPDS(p2);
> >    else
> >       return calcFPDS(p1);
> > }
> >
> > where isNullable(p) checks whether p can match the empty sequence (and
any
> > atts)?
>
> No. Firstly, there are two patterns that needs the second fpds parameter.
>
>     if(p is "<attribute />")
>       return fpds
>
>     if( p is <empty/> )
>       return fpds

isNullable() would mean nullable with respect to the children not the
attributes, ie

isNullable("<attribute/>") would be true

> Secondly, in case of <group> p1 p2 </group>, p2 may also be nullable
> (AKA epsilon-reducible). In that case, we still need the second
> parameter.

Yes, but that would only make a difference if that groups is in turn inside
a group:

<group><group>p1 p2</group> p3</group>

The outer group would then check whether the inner group is nullable, and
max with p3 if it was.

James