C# Eval Function

devilplusplus

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Mar 6, 2006

CPOL

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C# eval function

Introduction

This article is about a C# eval function, how to parse an expression and evaluate it. It supports Boolean, Bitwise, Arithmetic, Unary, Paren, Member (such as object.property), Indexer (such as array[index]) and ConditionalIf(?:), it also supports Variable assign.

You can use it to evaluate one statement in the C# source code.

It does not use runtime compiler.

It does not use JScript.NET.

It does not use DataTable.

Using the Code

Expression Example

Basic

2+3*5
 true||false
 a+b*c
 a.b+c.d
 a.f(1,2)[b]
 "123"[0]
 "123".Length
 (1).ToString()

All functions or properties use Reflection to eval. It has no global function and its syntax is checked at runtime.
If you let Parameter 'string'=typeof(string), then it can do like this:

string.Format("{0}1111",233)

If a parameter is a type, it will call its static function or property.

Advanced

(a>b)?c:d

Reflection

("To"+"String")()

Sample Use

using System;
using Jyc.Expr;
namespace TestExpr
{
    class Program
    {
        static void Main(string[] args)
        {
            Parser ep = new Parser();
            Evaluater evaluater = new Evaluater();
            ParameterVariableHolder pvh = new ParameterVariableHolder();

            pvh.Parameters["char"] = new Parameter(typeof(char));
            pvh.Parameters["sbyte"] = new Parameter(typeof(sbyte));
            pvh.Parameters["byte"] = new Parameter(typeof(byte));
            pvh.Parameters["short"] = new Parameter(typeof(short));
            pvh.Parameters["ushort"] = new Parameter(typeof(ushort));
            pvh.Parameters["int"] = new Parameter(typeof(int));
            pvh.Parameters["uint"] = new Parameter(typeof(uint));
            pvh.Parameters["long"] = new Parameter(typeof(string));
            pvh.Parameters["ulong"] = new Parameter(typeof(ulong));
            pvh.Parameters["float"] = new Parameter(typeof(float));
            pvh.Parameters["double"] = new Parameter(typeof(double));
            pvh.Parameters["decimal"] = new Parameter(typeof(decimal));
            pvh.Parameters["DateTime"] = new Parameter(typeof(DateTime));
            pvh.Parameters["string"] = new Parameter(typeof(string));

            pvh.Parameters["Guid"] = new Parameter(typeof(Guid));

            pvh.Parameters["Convert"] = new Parameter(typeof(Convert));
            pvh.Parameters["Math"] = new Parameter(typeof(Math));
            pvh.Parameters["Array "] = new Parameter(typeof(Array));
            pvh.Parameters["Random"] = new Parameter(typeof(Random));
            pvh.Parameters["TimeZone"] = new Parameter(typeof(TimeZone));
            pvh.Parameters["AppDomain "] = new Parameter(typeof(AppDomain));

            pvh.Parameters["Console"] = new Parameter(typeof(Console));

            pvh.Parameters["evaluater"] = new Parameter(evaluater);

            evaluater.VariableHolder = pvh;

            while (true)
            {
                System.Console.WriteLine("Input line,press Return to Eval:");
                string line = System.Console.ReadLine().Trim();
                if (string.IsNullOrEmpty(line))
                    break;
                try
                {
                    Tree tree = ep.Parse(line);

                    tree.Print(System.Console.Out);

                    object result = evaluater.Eval(tree);

                    if( result != null )
                        System.Console.WriteLine("Result:{0}", result);
                    else
                        System.Console.WriteLine("Result is null");
                }
                catch (Exception e)
                {
                    System.Console.WriteLine("Exception:" + e.GetType().Name _
                                               +"->"+ e.Message);
                }
            }
        }
    }
}