SetDefaultNumberType(DefaultNumberType.Decimal) can't access any default library like string related or Math related functions in DynamicExpresso

Question

I am working on a Blazor WebAssembly project using .NET 8, and I am utilizing the DynamicExpresso library to evaluate my expressions.

If we use interpreter.SetDefaultNumberType(DefaultNumberType.Decimal) , then we can't access any default library like string related or Math related functions etc.

interpreter = new Interpreter().SetDefaultNumberType(DefaultNumberType.Decimal);

After this if we try to evaluate below string for a loaded variable strVariable , Below expression will not evaluate.

strVariable.Substring(0, 40)

if we create the interpreter with this interpreter = new Interpreter() then above expression will evaluate.

I have tried to add reference for the string and Math lib as below , but it still does not work , it only works if we remove the SetDefaultNumberType option.

 interpreter = interpreter.Reference(typeof(System.String));
 interpreter = interpreter.Reference(typeof(System.Math));

can someone help on this issue. as we need to set Default Number Type and also have some access to libraries for extension methods etc.

For Example:

using DynamicExpresso;

var interpreter = new Interpreter();
var result = interpreter.Eval("\"abcdefg\".Substring(2)");
Console.WriteLine(result.ToString());

This code is working Perfectly And

using DynamicExpresso;

var interpreter = new Interpreter();
interpreter.SetDefaultNumberType(DefaultNumberType.Decimal);
var result = interpreter.Eval("\"abcdefg\".Substring(2)");
Console.WriteLine(result.ToString());

And this code show Error that substring not found.

I need both string functions and DeafaultNumber=Decimal.

Any guidance or suggestions would be greatly appreciated.