// C# Eval Expression

// Doc: https://eval-expression.net/my-first-evaluation

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// @nuget: Z.Expressions.Eval

​

/*

## Use Option to Add Keyword

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In the C# Eval Expression library, you can add your own `keyword`. You cannot override existing keywords, but you can create new ones, such as `isin`, that will check if the current item is in the list.

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In this example, we will create an extension method named `IsIn` that checks if an item is part of a list. Then, we will create the keyword `isin` that will be bound to this extension method and can be used directly in the expression:

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See more: https://eval-expression.net/my-first-evaluation

*/

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using System;

using System.Collections.Generic;

using Z.Expressions;

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public class Program

{

    public static void Main()

    {

        EvalManager.DefaultContext.RegisterExtensionMethod(typeof(CustomExtensions));

        EvalManager.DefaultContext.RegisterKeyword("isin", "IsIn");

        var list = new List<int>() { 1, 2, 3 };

        Console.WriteLine(Eval.Execute("2 isin list", new { list }));

        Console.WriteLine(Eval.Execute("4 isin list", new { list }));

    }

}

​

public static class CustomExtensions

{

    public static bool IsIn<T>(this T x, List<T> list)

    {

        return list.Contains(x);

    }

}