Discussion List Archives

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [ddlm-group] Use of elides in strings

Hi all,

In a previous posting I registered PDB preference to leave the interpretation
of elided characters to the application.    I am not presently aware of cases
from our work where it would be useful to introduce handling of elides within
the CIF syntax.  I am particularly worried about any lexical interpretation
of '\' that may interfere with their use in regular expressions which we
have a significant dependency in our dictionaries.    I continue to vote for the
particular interpretation of '\' and other special characters be defined
by the dictionary definition of the item.   I think this provides the greatest
flexibility for all applications.



Herbert J. Bernstein wrote:
> Dear Colleagues,
>   My personal preference would be to leave things in what to me seems the
> simpler approach of passing all reverse solidus glyphs to the application.
> However, the pragmatics achieving a consensus and getting on with coding 
> is more important that my personal taste.
>   The major impact of a chnage un the handling of the reverse solidus in
> having some of them absorbed by the CIF2 parsers would be in then
> handling of legacy CIFs at the IUCr and at the PDB.  James is right
> that what we are discussing is the difference between raw and cooked
> python strings.  Inasmuch as CIF2 is now going to forbid the use of
> quote marks within non-delimited strings, in order to make the
> conversion of legacy CIFs from CIF1 to CIF2 as easy as possible,
> may I suggest that we adopt both cooked and raw quoted strings
> from python, so that r"  and r' can be used to introduce any raw, 
> unconverted string taken from a CIF1 in which almost all existing
> CIF1 reverse solidus behavior could be left untouched, and that
> we accept James cooked approach for quoted strings not marked with
> the r' or r".
>   What say the IUCr journal operation and the PDB?  It is their ox we 
> are goring here.
>   Regards,
>     Herbert
> =====================================================
>  Herbert J. Bernstein, Professor of Computer Science
>    Dowling College, Kramer Science Center, KSC 121
>         Idle Hour Blvd, Oakdale, NY, 11769
>                  +1-631-244-3035
>                  yaya@dowling.edu
> =====================================================
> On Thu, 19 Nov 2009, James Hester wrote:
>> OK, fair enough.  Just to clarify, I am not advocating the full
>> repertoire of backslash elides, only two specific ones:
>> <backslash><terminator> and <backslash><backslash>.  Any other use of
>> backslash would simply leave that backslash untouched.
>> Would suggesting that the cut-and-pasters restrict themselves to
>> semicolon-delimited strings or triple-quote delimited strings help
>> with legacy issues?
>> Anyway, let us await the opinions of our Western Hemisphere colleagues...
>> On Thu, Nov 19, 2009 at 7:02 PM, Nick Spadaccini 
>> <nick@csse.uwa.edu.au> wrote:
>>> On 19/11/09 12:58 PM, "James Hester" <jamesrhester@gmail.com> wrote:
>>>> We need to figure out the behaviour of elides.  This was previously
>>>> discussed in a thread entitled "The alphabet of non-delimited
>>>> strings", especially in messages around Oct 16th.  The behaviour
>>>> advocated by Nick is for both the eliding and elided character to be
>>>> returned from the parser.  The behaviour I would prefer is for the
>>>> eliding character to disappear; it should itself be elided if it is to
>>>> remain in the string.
>>>> To summarize Nick's and Herbert's arguments from the emails dated Fri
>>>> Oct 16, 2009 at 6:22AM and subsequently
>>>> 1. We don't interpret elides because we don't know what algorithm to
>>>> use (i.e. it might be a greek character sequence)
>>>> 2. The elide simply signals that the lexer should not interpret the
>>>> following character
>>>> My counter-proposal is similar to Simon's original expectation: if the
>>>> elide character is really eliding a syntactically significant
>>>> character (i.e. a terminator character or an elide character), the
>>>> elide sequence is replaced by the single character.  I counter the
>>>> above arguments as follows:
>>>> (a) The profusion of algorithms for backslash processing is
>>>> irrelevant. We can interpret the elides because the only algorithm
>>>> that has any relevance at the parser level is the simple
>>>> <backslash><character> -> <character>.  All other potential uses
>>>> belong to higher levels.  If the higher levels require a
>>>> <backslash><quote>, that is created by writing
>>>> <backslash><backslash><backslash><quote> in the on-disk string.
>>> Couldn't agree with you more, and you are preaching to the converted who
>>> were converted away by others. This is what I was arguing months ago 
>>> for how
>>> to interpret the """ strings. That is \n (EXPLICITLY THE ASCII REVERSE
>>> SOLIDUS) is always a newline, \t is always a tab etc. The parser should
>>> always substitute the single binary character for these character 
>>> doublets
>>> ala unix/python/C etc. And you quite rightly argue if you want \n to 
>>> really
>>> mean the IUCr Greek nu then it will have to be \\n, and the same 
>>> parser will
>>> give the downstream application \n (having removed the leading elide).
>>> Beautiful, that's what the computer scientist in me argues.
>>> However others argued that many users vim/emacs the file and cut and 
>>> paste
>>> the text content. So if you have a LaTEX string "{\\em I am italicised}"
>>> that you cut and paste then it fails.  And the blasted backward
>>> compatibility argument comes in with existing CIF1 files that are not 
>>> doubly
>>> elided.
>>> What we can do is push the idea that a CIF2 string is a COMPLETELY 
>>> different
>>> beast to a CIF1 string. We know that with CIF1 data names and data 
>>> values we
>>> have to push our CIF2 parser in to a different grammar to handle things
>>> correctly. At that level elides in a string will have a strict CIF1 
>>> meaning
>>> (ie IUCr Greek markup).
>>> In CIF2 an elide in a string protects the following character from being
>>> interpreted as a delimiter. There is special meaning for \n, \t etc 
>>>  which
>>> are replaced by their single character. \u123456 (up to 6 hex numbers)
>>> indicate a unicode character which should be replaced by the correct 
>>> byte
>>> sequence. All other first reverse solidus should be removed, and the
>>> immediately following character passed on as part of the string. 
>>> Characters
>>> can be (multibyte) UTF-8.
>>> If you want to encode LaTEX (or IUCr-speak or something similar) then 
>>> you
>>> are going to have double all your reverse solidii. You can't cut and 
>>> paste
>>> from an editor - bad luck.
>>> I will wait for Herb's response to this because he was an advocate of
>>> leaving things as they were (I think). I am happy to move forward 
>>> with your
>>> suggested interpretation.
>>>> (b) The profusion of algorithms for backslash processing means that
>>>> we *must* remove ambiguity by removing the eliding character during
>>>> processing; otherwise, an application can't tell if it is e.g. looking
>>>> at an escaped prime or an acute accent without applying ugly
>>>> heuristics.  Note also that a caller of a CIF reading program doesn't
>>>> currently need to know what the particular string delimiting character
>>>> was for a given string value; in order to make a guess at what
>>>> the backslash might mean, it would often need to know this.
>>>> It appears that Nick is describing Python raw string behaviour,
>>>> and I am describing Python 'cooked' string behaviour.  Note for the
>>>> following paragraph from
>>>> docs.python.org/reference/lexical_analysis.html#strings:
>>>> When an 'r' or 'R' prefix is present, a character following a
>>>> backslash is included in the string without change, and all
>>>> backslashes are left in the string. For example, the string
>>>> literal r"\n" consists of two characters: a backslash and a
>>>> lowercase 'n'. String quotes can be escaped with a backslash,
>>>> but the backslash remains in the string; for example, r"\"" is
>>>> a valid string literal consisting of two characters: a
>>>> backslash and a double quote; r"\" is not a valid string
>>>> literal (even a raw string cannot end in an odd number of
>>>> backslashes). Specifically, a raw string cannot end in a
>>>> single backslash (since the backslash would escape the
>>>> following quote character). Note also that a single backslash
>>>> followed by a newline is interpreted as those two characters
>>>> as part of the string, not as a line continuation.
>>>> Note that raw strings cannot end in a backslash, so I would consider
>>>> them slightly less expressive than cooked strings, which can express
>>>> everything.
>>>> I would challenge Nick et. al. to explain what the advantage
>>>> of keeping the eliding character in the datavalue is, keeping in mind
>>>> that programs like CIFtbx and PyCIFRW and several others aim to hide
>>>> CIF syntax from their users (as a service), and this proposal appears
>>>> to want to expose a confusing part of it to them.  Some questions we
>>> The original "advantage" (if you could call it that) was to keep others
>>> happy and to support backwards compatibility.
>>>> toolbox maintainers will need to ask if this goes through: Do you
>>>> handle escaping any strings passed to you for output?  How do you know
>>>> if the caller has done the escaping already, or not?  Do you really 
>>>> expect
>>>> the calling software to work out whether it wants a single or double
>>>> or triple quote delimited string?  Isn't that the service provided by
>>>> your software?  What are they (not) paying you for, anyway?
>>> When they pay, I'll answer that question!
>>> cheers
>>> Nick
>>> --------------------------------
>>> Associate Professor N. Spadaccini, PhD
>>> School of Computer Science & Software Engineering
>>> The University of Western Australia    t: +61 (0)8 6488 3452
>>> 35 Stirling Highway                    f: +61 (0)8 6488 1089
>>> CRAWLEY, Perth,  WA  6009 AUSTRALIA   w3: www.csse.uwa.edu.au/~nick
>>> MBDP  M002
>>> CRICOS Provider Code: 00126G
>>> e: Nick.Spadaccini@uwa.edu.au
>>> _______________________________________________
>>> ddlm-group mailing list
>>> ddlm-group@iucr.org
>>> http://scripts.iucr.org/mailman/listinfo/ddlm-group
>> -- 
>> T +61 (02) 9717 9907
>> F +61 (02) 9717 3145
>> M +61 (04) 0249 4148
>> _______________________________________________
>> ddlm-group mailing list
>> ddlm-group@iucr.org
>> http://scripts.iucr.org/mailman/listinfo/ddlm-group
> ------------------------------------------------------------------------
> _______________________________________________
> ddlm-group mailing list
> ddlm-group@iucr.org
> http://scripts.iucr.org/mailman/listinfo/ddlm-group
ddlm-group mailing list

Reply to: [list | sender only]
International Union of Crystallography

Scientific Union Member of the International Science Council (admitted 1947). Member of CODATA, the ISC Committee on Data. Partner with UNESCO, the United Nations Educational, Scientific and Cultural Organization in the International Year of Crystallography 2014.

International Science Council Scientific Freedom Policy

The IUCr observes the basic policy of non-discrimination and affirms the right and freedom of scientists to associate in international scientific activity without regard to such factors as ethnic origin, religion, citizenship, language, political stance, gender, sex or age, in accordance with the Statutes of the International Council for Science.