I have come across what I beleive is a bug in the VsSdk babel support code
for MPPG .
Below is a description of the bug a fix for it - so far this fix hasn't
caused any ill side-effects.
Does anyone know if this is a known issue ?
Is a list of known bugs & fixes for the VsSdk available somewhere ?

Gerry

using the following MPLEX specification :

   %%
   SECTION1            return (int)(Tokens.SECTION1);
   SECTION2            return (int)(Tokens.SECTION2);
   [.\n]*                       /* ignore */
   %%

and using the following MPPG grammer :

   %token    SECTION1 SECTION2
   %%
   Program:        Section1 Section2 ;
   Section1:
           |        SECTION1 ;
   Section2:
           |        SECTION2 ;
   %%

parsing the following input using MPPG :

      SECTION2

Will result in an error IndexOutOfRangeException in ShiftReduceParse.cs at
the line indicated below.
This error seems to happen whenever the 1st rule in the start rule is
optional and is not present in the data being parsed.
The following code includes a fixes for the problem.

ShiftReducedParser.cs line 124
124:         Rule rule = rules[rule_nr];

               //
               // Default action "$$ = $1" for unit productions.
               //
-->           // if (rule.rhs.Length == 1)
-->           if ( rule.rhs.Length < 2 )
                   yyval = value_stack.Top(); // default action: $$ = $1;
               else
                   yyval = new YYSTYPE();
               //
               // Default action "@$ = @1.Merge(@N)" for location info.
               //
-->          // if (rule.rhs.Length == 1)
-->          if ( rule.rhs.Length < 2 )
                   yyloc = location_stack.Top();
               else
               {
exc -->        YYLTYPE at1 = location_stack.array[location_stack.top -
rule.rhs.Length];
                   YYLTYPE atN = location_stack.array[location_stack.top -
1];
                   if (at1 != null && atN != null) yyloc = at1.Merge(atN);
               }
               DoAction(rule_nr);