Re: Parse multiple versions of a document format?

[tys lefering]

On Thu, October 8, 2009 14:34, Hans Aberg wrote:
> On 8 Oct 2009, at 09:55, Rui Maciel wrote:
>
>> I'm writing a parser for a document format which has a couple of
>> version out.
>> The document format basically consists of a header field, where the
>> document
>> format version is specified and whose format is the same across all
>> format
>> versions, followed by multiple fields which differ between versions.
>>
>> Having that case in mind, what is the best strategy to write a bison
>> parser
>> that is capable of parsing multiple versions of a document format?
>
it is easy to have multiple generated parsers in one program
and switch between them depending on version and possibly also
easy to maintain.
example how to do this is in gettext package in po-gram-gen.y
http://savannah.gnu.org/projects/gettext
it is using macros to remap parser variables like this
and it works using bison yacc and glr grammars.

/* Remap normal yacc parser interface names (yyparse, yylex, yyerror, etc),
   as well as gratuitiously global symbol names, so we can have multiple
   yacc generated parsers in the same program.  Note that these are only
   the variables produced by yacc.  If other parser generators (bison,
   byacc, etc) produce additional global names that conflict at link time,
   then those parser generators need to be fixed instead of adding those
   names to this list. */

#define yymaxdepth po_gram_maxdepth
#define yyparse po_gram_parse
#define yylex   po_gram_lex
#define yyerror po_gram_error
#define yylval  po_gram_lval
#define yychar  po_gram_char
#define yydebug po_gram_debug
#define yypact  po_gram_pact
#define yyr1    po_gram_r1
#define yyr2    po_gram_r2
#define yydef   po_gram_def
#define yychk   po_gram_chk
#define yypgo   po_gram_pgo
#define yyact   po_gram_act
#define yyexca  po_gram_exca
#define yyerrflag po_gram_errflag
#define yynerrs po_gram_nerrs
#define yyps    po_gram_ps
#define yypv    po_gram_pv
#define yys     po_gram_s
#define yy_yys  po_gram_yys
#define yystate po_gram_state
#define yytmp   po_gram_tmp
#define yyv     po_gram_v
#define yy_yyv  po_gram_yyv
#define yyval   po_gram_val
#define yylloc  po_gram_lloc
#define yyreds  po_gram_reds          /* With YYDEBUG defined */
#define yytoks  po_gram_toks          /* With YYDEBUG defined */
#define yylhs   po_gram_yylhs
#define yylen   po_gram_yylen
#define yydefred po_gram_yydefred
#define yydgoto po_gram_yydgoto
#define yysindex po_gram_yysindex
#define yyrindex po_gram_yyrindex
#define yygindex po_gram_yygindex
#define yytable  po_gram_yytable
#define yycheck  po_gram_yycheck