anchor.diff:   */
   tree grammar SparqlT; 
   
  -options {
  +options { 
   tokenVocab=Sparql; // reuse token types
   ASTLabelType=CommonTree; // $label will have type CommonTree
   output=template; //template;
  
positive.code: 
  constraint
      : e=brackettedExpression -> constraint(brackettedExpression={$e.st})
      | b=builtInCall -> constraint(expression={$b.st})
      | f=functionCall -> constraint(expression={$f.st})
      ;
  
  functionCall
  
negative.code:     ;
  
  blankNode
      : BLANK_NODE_LABEL -> blankNode(value={$BLANK_NODE_LABEL.text})
      | a=anon -> blankNode(anon={$a.st})
      ;
  
  