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RE: Parsing of comments in BNC definition

  • Subject: RE: Parsing of comments in BNC definition
  • From: "Bollinger, John Clayton" <jobollin@xxxxxxxxxxx>
  • Date: Wed, 29 Nov 2000 18:31:50 GMT

Nick Spadaccini wrote:
[James Hester wrote:]
> > The beginning of a file would have to have honorary 'terminate'
> > status, otherwise a hash as first character in the file 
> wouldn't count
> > as a comment.  
> 
> Yes that's right James. I've noted that also, and it is 
> difficult to get
> around without introducing other new production items. If you haven't
> followed this discussion list before James, I have said it often that
> requiring productions for comments complicates things considerably.
> That's why most systems just strip comments out at the lexical level.

Here's another complication I just noticed: in the current BNF,
whitespace is permitted only within the context of a data block
production.  That's a fairly minor detail, but it does mean that no
whitespace of any kind can be present in a CIF without any data block.
I don't think that is the correct behavior; it is certainly not
consistent with the canonical results included with Brian's ciftest
suite.

It appears that this could be corrected by moving the <wspace>* from
the beginning of the <data_block> production to the beginning of the
<CIF_file> production.  The <data_block> production already handles
whitespace after the last datum of a data block, so this also would
disambiguate a minor issue involving how to parse whitespace between
two data blocks.

Regards,

John

--

John C. Bollinger, PhD
Indiana University
Molecular Structure Center

jobollin@indiana.edu

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