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[ddlm-group] THREAD 2: token delimiters

  • To: Group finalising DDLm and associated dictionaries <ddlm-group@iucr.org>
  • Subject: [ddlm-group] THREAD 2: token delimiters
  • From: Nick Spadaccini <nick@csse.uwa.edu.au>
  • Date: Thu, 17 Sep 2009 13:54:24 +0800
  • Authentication-Results: postfix;
In trying to strictly define the data types in Star/CIF and introducing
compound (recursive) data structures has required a bit of a rethink so that
we can simplify things.

The following tokens are accepted by Star/CIF

(1) An un-delimited string - for which I will introduce some restrictions
(separate THREAD).
(2) A single quote (') delimited string.
(3) A double quote (") delimited string.
(4) A semi-colon (\n;) delimited string.

All four are well established and understood, not-with-standing some changes
to (1).


(5) A triple quote (""") delimited string - same as semi-colon delimited
with the possibility of same parsing requirements (separate THREAD)
(6) The List ([]) compound data structure. Well understood in the
literature, comma delimited, recursive, includes all other token types given
(7) The Table ({}) compound data structure. AKA an Associative Array, Python
Dictionary etc. It is the same as a List except indexed by a string (either
single or double quote).

What has been deleted from the specification is

(-1) The triple single quote (''') string. This is just redundant and
duplicates identically the behaviour of the """ string.
(-2) The Tuple (()) compound data structure. The Tuple's immutability is a
(relatively) subtle implementation behaviour, which has no meaning at a
syntactic level. Since Star/CIF clearly separates representation from
implementation, reference to Tuples is not meaningful. It also simplifies
the scanner, since it will avoid confusion with Measured types that have the
form Number(Unsigned Integer).

Opinions please. Please use the appropriate reply facility on your mail
application. I want these threads to be clearly identified and separated by
their subject titles.



Associate Professor N. Spadaccini, PhD
School of Computer Science & Software Engineering

The University of Western Australia    t: +61 (0)8 6488 3452
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e: Nick.Spadaccini@uwa.edu.au

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