// ================================================================================================
// BlockContext stores the information needed when creating an alternative (list of elements).
// Entering a subrule requires that we save this state as each block of alternatives requires
// state such as "tail of current alternative."
// ================================================================================================
unit dpglib.BlockContext;

interface
uses
   dpglib.types;

type
   TBlockContext = class(TObject)
      private
         fAltNum     : integer;
         fBlock      : IAlternativeBlock;
         fBlockEnd   : IBlockEndElem;

      public
         procedure   AddAlternativeElem( pElem: IAlternativeElem); virtual;

         function    CurrentAlt  : IAlternative;
         function    CurrentElem : IAlternativeElem;

      public
         property    AltNum   : integer            read  fAltNum     write fAltNum;
         property    Block    : IAlternativeBlock  read  fBlock      write fBlock;
         property    BlockEnd : IBlockEndElem      read  fBlockEnd   write fBlockEnd;
   end;


implementation
// ----------------------------------------------------------------------------
// CurrentAlt
// ----------------------------------------------------------------------------
function TBlockContext.CurrentAlt: IAlternative;
begin
   fBlock.Alternatives.Items[fAltNum].QueryInterface( IAlternative, result);
end;

// ----------------------------------------------------------------------------
// CurrentElem
// ----------------------------------------------------------------------------
function TBlockContext.CurrentElem: IAlternativeElem;
begin
   result := CurrentAlt.Tail;
end;

// ----------------------------------------------------------------------------
// AddAlternativeElem
// ----------------------------------------------------------------------------
procedure TBlockContext.AddAlternativeElem(pElem: IAlternativeElem);
begin
   CurrentAlt.AddElem( pElem);
end;

end.