chl at clw.cs.man.ac.uk
Thu Mar 8 02:51:51 PST 2001
In <877l21qu5u.fsf at erlenstar.demon.co.uk> Andrew Gierth <andrew at erlenstar.demon.co.uk> writes:
>>>>>> "Clive" == Clive D W Feather <clive at demon.net> writes:
> Clive> wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
>I reiterate my objection that a single wildmat, and a comma-delimited
>list of (possibly negated) wildmats, are separate syntactic entities
>and should not be combined in this way.
>The combined approach disguises the fact that we are making
>incompatible changes to commands such as LIST ACTIVE, and has no
>justification either from a specification or implementation point of
It provides a useful extension of functionality (one which I would have
found useful on several occasions in the past), whilst at the same time
providing a generalisation of several situations which currently differ
only for arbitrary reasons (for example NEWNEWS and LIST NEWSGROUPS).
AIUI, the extension (or something very close to it) is already present in
> In fact, the present text severely interferes with attempts to
>handle complex pattern lists efficiently.
I don't see why. In any case, complex pattern lists are unlikely to arise
during routine newsreading or transport (with the exception of NEWNEWS,
which already has this feature). Complex patterns will arise most often
when users are making rather specific enquiries, and these will be few
enough that efficiency need not be the prime consideration.
> Clive> [W6: the grammar does not treat , in sets as special. This
> Clive> means that the wildmat "a[b,c]d" is a single pattern that
> Clive> matches the three strings "abd", "a,d", and "acd". Are we
> Clive> happy with this ? It matches existing practice
>it does no such thing. Existing practice, where a list of wildmats is
>expected, treats ',' as a delimiter without any escape mechanism (and
>none is needed).
There is NO EXISTING PRACTICE on this. For a start, the whole wildmat-set
business is new since RFC 977, so there is no existing definition in the
matter (and it only arises in the NEWNEWS command currently).
Then, in the second place, wildmats have (apart from XPAT) only ever been
used to match newsgroup names (and this will remain true). Since ','
cannot occur within a newsgroup name (for obvious reasons) it is
impossible for this case ever to have arisen in the past; nor will it
ever arise under our present proposal.
And in the case of XPAT, if it has ever arisen it SHOULD NOT have been
treated as a separator of alternative patterns because that has not been a
feature of wildmats until now. Implementors who continue to offer XPAT
will have to decide what to do in this new situation, and following
Clive's suggestion is likely as easy a way for them to proceed as any
other; certainly, existing practice does not enter into it.
> Clive> but means that you can't split a wildmat into the component
> Clive> patterns just by looking for unescaped commas.
>which is intolerable.
Charles H. Lindsey ---------At Home, doing my own thing------------------------
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