anchor.diff:    FunctionCall(this.target, this.args);
   
     @override
  -  dynamic visit(AstVisitor visitor, [dynamic context]) =>
  +  R visit<R, C>(AstVisitor<R, C> visitor, [C context]) =>
         visitor.visitFunctionCall(this, context);
   }
   
  
positive.code:   AST falseExp;
    Conditional(this.condition, this.trueExp, this.falseExp);
    @override
    dynamic visit(AstVisitor visitor, [dynamic context]) =>
        visitor.visitConditional(this, context);
  }
  
  
negative.code:   SafeMethodCall(this.receiver, this.name, this.args);
  
    @override
    R visit<R, C>(AstVisitor<R, C> visitor, [C context]) =>
        visitor.visitSafeMethodCall(this, context);
  }
  
  