anchor.diff:  }
   
   class InvokeFunctionExpr extends Expression {
  -  Expression fn;
  -  List<Expression> args;
  +  final Expression fn;
  +  final List<Expression> args;
     InvokeFunctionExpr(this.fn, this.args, [OutputType type = null])
         : super(type);
   
  
positive.code: }
  
  class InstantiateExpr extends Expression {
    Expression classExpr;
    List<Expression> args;
    InstantiateExpr(this.classExpr, this.args, [OutputType type]) : super(type);
  
    dynamic visitExpression(ExpressionVisitor visitor, dynamic context) {
  
negative.code: }
  
  class WriteVarExpr extends Expression {
    final String name;
    final Expression value;
    WriteVarExpr(this.name, Expression value, [OutputType type = null])
        : this.value = value,
          super(type ?? value.type);
    dynamic visitExpression(ExpressionVisitor visitor, dynamic context) {
      return visitor.visitWriteVarExpr(this, context);
    }
  