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Re: [bug-bison] Bug in string-valued terminals

From: Tom Roberts
Subject: Re: [bug-bison] Bug in string-valued terminals
Date: Fri, 07 Jan 2011 16:08:21 -0600
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On 12/29/10 12/29/10 - 7:31 PM, Joel E. Denny wrote:
On Wed, 29 Dec 2010, Tom Roberts wrote:
Ok. I decided to not use yytoknum[], as it is undocumented and also requires a
funky "#define YYPRINT". Here is the code I am using inside yylex():
[... some important lines omitted at beginning and end ...]
                 for(int i=0; i<YYNTOKENS; ++i) {
                         if(yytname[i][0] != '"') continue;
                         string name(yytname[i]+1);
                         for(int j=YYMAXUTOK; j>0; --j) {
                                 if(yytranslate[j] == i) {
                                         keyword[name] = j;

Isn't your inner loop sufficient?  The body could just translate and index
into yytname.

Both loops are needed -- the outer one is over the string-valued tokens, and the inner one inverts yytranslate[] for the current string token. Note that I am doing this only on the first call to yylex(), to fill up keyword[] (see my previous email for the complete C++ code snippet). From then on I just query keyword[] -- I decided to do the nested loops just once, and then use the much faster lookup in keyword[] (which is a std::map<string,int>, not an array).

In any case, YYMAXUTOK and yytranslate are not documented for users

Yes. Perhaps they should be. Or perhaps there should be some method for yylex() to return a token # that does not get passed through yytranslate[] (e.g. a negative value, or a value with a large offset).

Again, it would be great if someone could recall how %token-table and the
yytname table it generates were originally intended to be used.  The
trouble is that yytname indices are internal token numbers, but there
seems to be no mechanism that is documented for the Bison user to
translate internal token numbers to user token numbers (which are the
token numbers returned by yylex).  How then is yytname useful?

I cannot help on this, as this is my first use of bison (but I used yacc extensively, many moons ago). BTW I'm happy with the workaround I described in my previous email.

Tom Roberts

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