anchor.diff:    }
   
     visitMutableVariable(cps_ir.MutableVariable node) {
  -    return "${node.runtimeType} ${names.name(node)}";
  +    return "MutableVariable ${names.name(node)}";
     }
   
     visitContinuation(cps_ir.Continuation node) {
  
positive.code:     String dummy = names.name(node);
      String variable = names.name(node.variable.definition);
      String value = formatReference(node.value);
      printStmt(dummy, '${node.runtimeType} $variable := $value');
      visit(node.body);
    }
  
  
negative.code: 
    visitLetMutable(cps_ir.LetMutable node) {
      String id = names.name(node.variable);
      printStmt(id, "LetMutable $id = ${formatReference(node.value)}");
      visit(node.body);
    }
  
  