Parsing Expression Grammar Support for C# 3.0 Part 1 - PEG Lib and Parser Generator

<<Grammar Name="BER" 
          encoding_class="binary"
          reference="http://en.wikipedia.org/wiki/Basic_encoding_rules"
          comment="Minimal tree generating BER decoder"
>>

{
   int tag,length,n,@byte;
   bool init_()     {tag=0;length=0;           return true;}
   bool add_Tag_()  {tag*=128;tag+=n;          return true;}
   bool addLength_(){length*=256;length+=@byte;return true;}
}

[1] ProtocolDataUnit: TLV;
[2] ^^TLV:  init_
     ( &BITS<6,#1> Tag ( #x80  CompositeDelimValue  #0#0 / Length CompositeValue )
     / Tag Length PrimitiveValue
     );
[3] Tag: OneOctetTag / MultiOctetTag / FATAL<"illegal TAG">;
[4] ^^OneOctetTag:   !BITS<1-5,#b11111> BITS<1-5,.,:tag>;
[5] ^^MultiOctetTag: . (&BITS<8,#1> BITS<1-7,.,:n> add_Tag_)* BITS<1-7,.,:n> add_Tag_;
[6] Length :   OneOctetLength / MultiOctetLength 
             / FATAL<"illegal LENGTH">;
[7] ^^OneOctetLength: &BITS<8,#0> BITS<1-7,.,:length>;
[8]^^MultiOctetLength: &BITS<8,#1> BITS<1-7,.,:n> ( .:byte addLength_){:n};
[9]^^PrimitiveValue: .{:length} / FATAL<"BER input ends before VALUE ends">;
[10]^^CompositeDelimValue: (!(#0#0) TLV)*;
[11]^^CompositeValue
{
     int len;
     PegBegEnd begEnd;
     bool save_()  {len= length;return true;}
     bool at_end_(){return len<=0;}
     bool decr_()  {len-= begEnd.posEnd_-begEnd.posBeg_;return len>=0;} 
}   :  save_ (!at_end_ TLV:begEnd 
              (decr_/FATAL<"illegal length">))*;
<</Grammar>>