c# convert string expression to a boolean expression [closed]

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Is it possible to convert a string expression into a boolean condition?

For example, I get the following string:

var b = "32 < 45 && 32 > 20"

I would like to create a bool expression out of this and invoke it. The string representation is also flexible (to make it more fun), so it allows ||, &&, ().

Also see how-can-i-evaluate-a-c-sharp-expression-dynamically?lq=1 — nawfal
– nawfal, Commented Dec 19, 2013 at 18:47

HDD · Accepted Answer · 2018-02-21 18:42:53Z

8

Have a look at Flee (Fast Lightweight Expression Evaluator) on CodePlex.

edited Feb 21, 2018 at 18:42

HDD

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answered Feb 17, 2011 at 13:45

RichardOD

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2 Comments

Silvair L. Soares Over a year ago

Man, what an incredible library! It worked perfectly for me. Thank you very much for your tip.

orlaqp Over a year ago

Thanks for pointing out this library @Richard, this is exactly what I needed!!!

Shakakai · Accepted Answer · 2011-02-17 13:52:35Z

5

I would use Irony, the .NET language kit. You could construct a simple grammar with Irony and then parse the string into executable command. There's a decent example of an arthmetic grammar in this tutorial and in the Expression Grammar Sample, its a pretty common request ;)

I definitely suggest using a proper compiler as opposed to Regex or a roll your own approach - it will be much more extensible if you ever want to add more rules.

answered Feb 17, 2011 at 13:52

Shakakai

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Stefan Dragnev · Accepted Answer · 2011-02-17 13:44:09Z

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If it follows all C# expression rules then compile it as dynamic code as per http://www.west-wind.com/presentations/dynamiccode/dynamiccode.htm

answered Feb 17, 2011 at 13:44

Stefan Dragnev

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3 Comments

Oskar Kjellin Over a year ago

How fast is that? I imagine it being quite slow

Stefan Dragnev Over a year ago

Not fast at all. Basically you invoke the C# compiler, which emits the IL of the expression, which is then wrapped in a method, then in a class, then in a dynamic assembly which is loaded into the current AppDomain, then you invoke the method through reflection to get the evaluation result. But it's a breeze to integrate, if it's just for a proof of concept or something...

Oskar Kjellin Over a year ago

Yes, I know how it works. I just wanted to point out that it would be a really slow way to do it

LukeH · Accepted Answer · 2011-02-17 14:14:17Z

1

If you're dealing with relatively simple mathematical expressions then a straightforward implementation of the shunting-yard algorithm should do the trick.

edited Feb 17, 2011 at 14:14

answered Feb 17, 2011 at 14:02

LukeH

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Community · Accepted Answer · 2019-04-05 00:39:26Z

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Take a look at my library, Proviant. It's a .NET Standard library using the Shunting Yard algorithm to evaluate boolean expressions. You could also implement your own grammar.

edited Apr 5, 2019 at 0:39

CommunityBot

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answered Apr 4, 2019 at 19:45

Genfood

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1 Comment

Paul Roub Over a year ago

Just linking to your own library or tutorial is not a good answer. Linking to it, explaining why it solves the problem, providing code on how to do so and disclaiming that you wrote it makes for a better answer. See: What signifies “Good” self promotion?

Valentin Kuzub · Accepted Answer · 2011-02-17 13:52:39Z

0

I think creating an interpreter for this string would not take too long time.

http://www.industriallogic.com/xp/refactoring/implicitLanguageWithInterpreter.html

here you can find information about design that can be used to create it.

answered Feb 17, 2011 at 13:52

Valentin Kuzub

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John xyz · Accepted Answer · 2011-02-17 14:06:42Z

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You could take a look at JINT (Javascript Interpreter for .NET) http://jint.codeplex.com/

answered Feb 17, 2011 at 14:06

John xyz

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