I guess that I should have explained better (I'm stil new with this, so I may not be asking the questions in the best way)


Normally, one would use the simple code:

if x>y then
something
end if


....but I have a text string stored on a database column that represents something that I want to evaluate. In other words, instead
of knowing that I want to see if x>y in advance, I only know that I wish to determine whether the string stored in some table column
is true or not at run time. Apparently the eval command/function does this in other languages, but not in VB.

Perhaps some of the references that others have listed might work - it will take time to read and digest.

If anyone can explain how to do this in very simple language that a beginner can understand, I would appreciate it.

Jeff

Jeff wrote:
Show quoteHide quoteJeff - there are some very good suggestions in that list, and depending
on the complexity of the expressions, then some of them maybe more
suitable then others (see Herfried's list).  Here is the one I was
suggesting.  This works really well if your expressions are simple
comparisons/mathmatical expressions - but it does require a little bit
of error trapping and input validation, because it can allow arbitrary
execution of jscript code, so it can potentially do dangerous things if
you aren't carefull with your input.

To use this suggestion:

1.  Create a file called evaluator.js and add the following code:

// JScript Source Code
class EvalClass
{
    function Evaluate(expression)
    {
        return eval(expression);
    }
}

2. start the vs.net command line and get to the directory where you
saved this file and type in the following command:

jsc /target:library evaluator.js

this will create a dll in that directory called evaluator.dll

3.  Create a simple console application in VS.NET and add a reference
to the compiled evaluator.dll and microsoft.jscript.dll.

4.  Here is the code:

Option Strict On
Option Explicit On

Imports System

Module Module1

    Sub Main()
        Dim s As String = "5>4"
        Dim e As New EvalClass()

        If DirectCast(e.Evaluate(s), Boolean) Then
            Console.ForegroundColor = ConsoleColor.DarkGreen
            Console.WriteLine("It Worked!")
        Else
            Console.ForegroundColor = ConsoleColor.DarkRed
            Console.WriteLine("It failed!")
        End If
    End Sub

End Module


You should get a green message that says "It Worked!".  Like I said, in
the production application, you'll want to make sure that the input to
EvalClass.Evaluate is safe.  If all your doing is simple
comparisons/mathmatical operations, then this is relatively easy to
accomplish with a couple lines of RegEx.

Is that simple enough?  Given these steps you can at least experiment
with it :)

Thanks, but again, I'm still in the early stages of learning. In other languages, this is
a simple built-in function. What is particularly frustrating is that there are so many small
variations of languages and scripts and similar, that if I find a possible answer on the
internet, I spend minutes if not hours eventually determining that it isn't applicable to
my Visual Web 2005 express edition.

For example, I've now searched just about everywhere for the simple piece of
information about how to open the vs.net command line that you mentioned. I can find no
..exe anywhere under various names mentioned through a google search, nor any type of
command line processor within the Visual Web GUI like in FoxPro.

So, can someone explain simply how to "open the vs.net command line"
Is this something not found in the Express version?

I understand the rest.

Thanks

Jeff

Jeff wrote:
While it's not in VB.NET - it is in JScript.NET.  What I am showing you
is a technique for exposing that to your VB.NET application.  This is
one of the great things about .NET.  You are able to use classes and
object written in other languages.

Well, there are limitations on the Express Editions.  But, in this case
it should be ok, because you have to compile the dll on the command
line :)

My guess is no.  It is simply a bat file that sets a bunch of
environment variables and then runs the command line.  Basically,
providing a .NET command line environment.  I'm pretty sure there is no
such thing with the express editions.  So, in your case you will either
need to add the framework directory to your path or type in the
complete path to the jsc.exe.  Example:

C:\> C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\jsc.exe
/target:library evaluator.js

Thanks for putting up with me. I've almost got it and it is one of the last snags I need to overcome to finish
a web application that I've been working months on. Please hang in here with me and point me in the direction of the one thing that
I'm still missing. To re-cap:

I have an "evaluator.js" file that looks like this:
// JScript File
class EvalClass
{
function Evaluate(expression)
{
return eval(expression);
}
}

I was able to create the evaluator.dll file. That .dll currently is in the ...\Framework\v2.0.50727\ folder

I created a "TestEvaluator.apsx" file on my server where I have the app. Here is the code (a slight variation of what you provided,
as I'm not sure I know what exactly you mean by a "console application." (isn't that for the regular vb and not for vweb?)

Here is the code in my TestEvaluator.aspx.vb
Option Strict On
Option Explicit On
Imports System
Partial Class TestEvaluator
    Inherits System.Web.UI.Page

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim s As String = "5>4"
        Dim g As New EvalClass()

        If DirectCast(g.evaluate(s), Boolean) Then
            Label1.Text = "It Worked"
        Else : Label1.Text = "It Failed"
        End If
    End Sub
End Class

I'm being told that, "Type EvalClass is not defined"
I'm sure that I need only a line or two more to make this work.
Can you please tell me what is missing?

Thanks very much - I'm almost there and can get all else working on my own if I can only get this example working (that simply
changes the label when the button is clicked)

Jeff

Never mind that last question of mine Tom. I was able to find the answer on my own right after posting.
Here it is for anyone attempting the same.

Thanks very much for the help and the step-by-step instructions for a newbee...
I've already started messing with the code and it appears to do what I need.

Jeff


To add an assembly DLL to your Web site project
  1.. In Solution Explorer, select your Web site.

  2.. On the Website menu, choose Add Reference. Alternatively, you can right-click the name of your Web site and then select Add
Reference.

  The Add Reference dialog box is displayed.

  3.. Select the Browse tab.

  4.. Navigate to the folder containing the assembly you want to reference, select the assembly, and then click OK.

  Adding a reference in this way ensures that all file dependencies (debug files, XML document files, and so on) are copied.

Jeff wrote:
I'm glad you got it working...  And I hope it does what you need.

Jeff,

See this sample created from some basic code we got from Charles Law.

http://www.vb-tips.com/dbPages.aspx?ID=34241f3e-16ff-4e87-86d1-2b03e1a439ae

I hope this helps,

Cor


Show quoteHide quote

Cor Ligthert [MVP] wrote:
Cor,

I personally would avoid using the MS Script control for several
reasons:

1.  It requires COM interop, so it can severaly impact performance if
it is used often.  I usually try to look for solutions that stay inside
of the framework if at all possible.

2.  It doesn't always work because windows scripting host is turned off
for security reasons.

3.  If I remember correctly (and I may not :), this particular control
has been broken in the past due to interface changes

I'm not saying that this isn't a valid solution - but wrapping the
JScript.NET eval function is fairly trivial, and it avoids the over
head of COM interop.  Still, as always, YMMV.

Tom,

I tried it and it works great. Charles made it first in a kind of fragmental
way and because there are so many questions about this I thought let me put
it on our website. Than it is of course set on that to show.

You should now that I am the one who is probably the most writing against
any not needed Com interop use, Api use, reflection use, and with that eval
use,  however I see so many people making propaganda for those, you should
forgive me this sine because this is so easy to use.

I see the one I have showed only to be used in a kind of demo situations,
not in real business.

Cor

Show quoteHide quote

Cor Ligthert [MVP] wrote:
Show quoteHide quoteCor,

I hope you don't think I was criticizing you or your answer.  Wrapping
the MS Script Control is a perfectly valid solution.  I was just
pointing out some of it's short commings, especially when you can
accomplish the task without going outside of the framework.

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