anchor.diff:  groupGraphPattern
       : ^(GROUP_GRAPH_PATTERN g=groupGraphPatternSub) -> groupGraphPattern(groupGraphPatternSub={$g.st})
       | ^(GROUP_GRAPH_PATTERN s=subSelect) -> groupGraphPattern(subselect={$s.st})
  -    | ^(GROUP_GRAPH_PATTERN GROUP_GRAPH_PATTERN) -> groupGraphPattern(attribute={"{ }"})
  +    | ^(GROUP_GRAPH_PATTERN GROUP_GRAPH_PATTERN) -> groupGraphPattern(attribute={""})
       ;
     
   groupGraphPatternSub
  
positive.code:     ;
  
  blankNode
      : BLANK_NODE_LABEL -> blankNode(value={"[ ]"})
      | a=anon -> blankNode(anon={$a.st})
      ;
  
  
negative.code:  */
  tree grammar SparqlT; 
  
  options { 
  tokenVocab=Sparql; // reuse token types
  ASTLabelType=CommonTree; // $label will have type CommonTree
  output=template; //template;
  