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Re: CIF parser / dialects

  • Subject: Re: CIF parser / dialects
  • From: James Hester <jrh@xxxxxxxxxxxx>
  • Date: Wed, 3 Jul 2002 05:06:42 +0100 (BST)
On Wed, 2002-07-03 at 03:00, Richard G. Ball wrote:
> If there is a concern over CIF dialects the easiest way to allay that concern and 
> inhibit present and future dialects is to provide an IUCr sponsored parser. It should> be in C and easily interfaced with the usual development languages (C (and its  > relatives), Perl, Python, Tcl, FORTRAN). Such a parser would conform to the IUCr specs. 
> for reading/writing CIFs and thereby form a solid base for higher 
>level tools. The situation we have now, with so many disparate parsers,
> is not very satisfactory (I have a partial one in Perl, James Hester
>has his in Python, there's Syd's & Herb's in FORTRAN and I am sure many
> others as well) and really should be addressed.
> If I have missed the creation of such a full-fledged, IUCr-approved, C-based parser
> I would appreciate a pointer to the code and I apologize for the
> Richard
> -- 

I think this proliferation is both inevitable and to be encouraged. 
Inevitable, because every author has different needs and circumstances
governing their choice of language: after all, in the beginning we had
CIFtbx in Fortran and an official parser in Fortran 77(QUASAR/vcif) but
that didn't stop us thinking about how useful it would be to have a
native C/C++ version.  As an example of the differing considerations at
different sites, I've gone with pure Python, as opposed to the much
faster Python with C/C++ back end option, for low-maintenance
portability combined with ease of installation - I distribute PyCifRW as
part of a larger program which is installed by non-programming-literate
people for the most part.  Maintaining a similar level of portability
with a C/C++ back end would mean (i) having to maintain n:n>=3
executable versions for easy distribution (impractical here) or (ii)
expecting compilation to be part of installation which is both expensive
in time and often money for the end user.

To be encouraged, because sooner or later there will be a parser for
everyone in the language they choose, thus lowering the barrier to the
spread of CIF software, and because, once some sort of official blessing
is obtained from the IUCr, there will be multiple reference

Which brings me to my final point (made a long time ago already on this
list or COMCIFS): given that inevitably others will want to write native
Perl/Lisp/Assembler parsers, a set of tricky tests which can be used for
automatic verification of a parser would be a key step forward.  The
current ciftest0-11 files are a useful start.  I have a little ciftest12
file which additionally catches some of the more obscure errors I've
made (the double terminating quotes, semicolon not in column 1,
trailing/leading carriage returns in semicolon strings) which I'll
contribute.  If COMCIFS could officially sanction a set of tests with
specifications on which must fail and which must pass, that would, I
think, be equivalent to an official IUCr reference implementation.

Other ideas for tricky tests: terminating semicolon followed by
non-blank (should fail); terminating semicolon followed by <eof> (pass).


James Hester, ANBF                             KEK
e-mail: jrh@anbf2.kek.jp                       Oho 1-1
Phone: +81 298 64 7959                         Tsukuba, Ibaraki 305
  Fax: +81 298 64 7967                         Japan

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