I need a fast runtime expression parser

Question

I need to locate a fast, lightweight expression parser.

Ideally I want to pass it a list of name/value pairs (e.g. variables) and a string containing the expression to evaluate. All I need back from it is a true/false value.

The types of expressions should be along the lines of:

varA == "xyz" and varB==123

Basically, just a simple logic engine whose expression is provided at runtime.

UPDATE
At minimum it needs to support ==, !=, >, >=, <, <=

Regarding speed, I expect roughly 5 expressions to be executed per request. We'll see somewhere in the vicinity of 100/requests a second. Our current pages tend to execute in under 50ms. Usually there will only be 2 or 3 variables involved in any expression. However, I'll need to load approximately 30 into the parser prior to execution.

UPDATE 2012/11/5
Update about performance. We implemented nCalc nearly 2 years ago. Since then we've expanded it's use such that we average 40+ expressions covering 300+ variables on post backs. There are now thousands of post backs occurring per second with absolutely zero performance degradation.

We've also extended it to include a handful of additional functions, again with no performance loss. In short, nCalc met all of our needs and exceeded our expectations.

don't know anything off-the-shelf, but doesn't seem too hard to write yourself (depending on requirements). Is == the only comparator? vars are case-sensitive as in C# or not case-sensitive as in vb.net? boolean operators allowed (and or not). Trying to figure out if this can really be any expression that you could write in code or users are limited to A=B — Suraj
– Suraj, Commented Dec 8, 2010 at 21:04
@Chris Lively, there are several good ways here stackoverflow.com/questions/1437964/… — acoolaum
– acoolaum, Commented Dec 8, 2010 at 21:09
> Quite often you parse the string only once and evaluate it often afterwards (eg with different arguments) NCalc mentioned below acheives this via a cache which works from multiple threads — GreyCloud
– GreyCloud, Commented Dec 10, 2010 at 13:41

David Makogon · Accepted Answer · 2017-11-06 16:24:58Z

36

Have you seen https://ncalc.codeplex.com/ and https://github.com/sheetsync/NCalc ?

It's extensible, fast (e.g. has its own cache) enables you to provide custom functions and varaibles at run time by handling EvaluateFunction/EvaluateParameter events. Example expressions it can parse:

Expression e = new Expression("Round(Pow(Pi, 2) + Pow([Pi2], 2) + X, 2)");

  e.Parameters["Pi2"] = new Expression("Pi * Pi");
  e.Parameters["X"] = 10;

  e.EvaluateParameter += delegate(string name, ParameterArgs args)
    {
      if (name == "Pi")
      args.Result = 3.14;
    };

  Debug.Assert(117.07 == e.Evaluate());

It also handles unicode & many data type natively. It comes with an antler file if you want to change the grammer. There is also a fork which supports MEF to load new functions.

It also supports logical operators, date/time's strings and if statements.

edited Nov 6, 2017 at 16:24

David Makogon

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answered Dec 9, 2010 at 9:29

GreyCloud

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7 Comments

ChrisLively Over a year ago

Just tested. Looks great. Still need to load test it, but the project was extremely easy to implement.

GreyCloud Over a year ago

ace, feel free to post in the Ncalc discussions page if you have any problems

ChrisLively Over a year ago

Just wanted to post an update after 7 months of usage. Simply put, it rocks. It is fast, very easy to implement, and even easier to extend with our own custom functions. I highly recommend nCalc.

GreyCloud Over a year ago

Thanks Chris, Great to hear :) I really enjoy working with the framework

NickLokarno Over a year ago

I can see in the unit tests of the code, that there's a test there to see if boolean expressions get short-circuited, so I guess the answer is yes.

|

Mason Wheeler · Accepted Answer · 2018-05-16 12:53:09Z

13

How about the Fast Lightweight Expression Evaluator? It lets you set variables and supports logical operators.

If you need something beefier and have the time, you could also design your own expression language with Irony.

edited May 16, 2018 at 12:53

Mason Wheeler

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answered Dec 8, 2010 at 23:21

Corbin March

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5 Comments

ChrisLively Over a year ago

I saw this but wasn't sure if anyone has actually used it. Do you have real world experience with it?

Corbin March Over a year ago

@Chris - I ran across it while tinkering with my own expression parser. It works as advertised but my requirements don't include fast so you may want to benchmark. Also, it may or may not be lightweight depending on how you define it ;).

ChrisLively Over a year ago

I upvoted you, but ultimately decided against this. After downloading it I saw it was all vb code; which I am sure is just fine but something in me (probably 20+ years of development) refuses to work with anything vb related if I have a choice. ;)

ISCI Over a year ago

For me. it faster than NCalc

Fandango68 Over a year ago

Or try this old chestnut. I still use it today and it works great. codeproject.com/Articles/19768/…

Toby · Accepted Answer · 2012-11-23 10:58:34Z

8

Hisystems' Interpreter supports custom functions, operators and literals, is lightweight pure c# portable code. Currently runs on iOS via MonoTouch and should run on any other Mono environment as well as windows. Free for commercial use. Available on GitHub at https://github.com/hisystems/Interpreter.

answered Nov 23, 2012 at 10:58

Toby

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Comments

Bijington · Accepted Answer · 2018-09-26 08:26:01Z

I fully appreciate how late this answer is however I would like to throw in my solution because I believe it can add more above the accepted answer of using NCalc should someone wish to use the expressions across multiple platforms.

-- Update --

I have created a parser for C# with plans to also implement it for Java and Swift over the next few months. This would mean that you can evaluate the expressions on multi-platforms without the need for tweaking per platform.

While Java and Swift was planned it never made it in to a fully fledge release. Instead there is now support for .NET Standard enabling support for Xamarin apps.

-- End update --

Expressive is the tool and it is available at: GitHub or Nuget.

The site has a fair amount of documentation on it but to prevent link rot here is an example on how to use it:

Variable support

var expression = new Expression("1 * [variable]");
var result = expression.Evaluate(new Dictionary<string, object> { ["variable"] = 2);

Functions

var expression = new Expression("sum(1,2,3,4)");
var result = expression.Evaluate();

It was designed to match NCalc as best as possible however it has added support for things like a 'null' keyword.

Olivier Duhart · Accepted Answer · 2017-09-30 09:01:11Z

1

self promotion here i wrote aa generic parser generator for c# https://github.com/b3b00/csly you can find an expression parseras example on my github. you may need to customize it to fit your needs

answered Sep 30, 2017 at 9:01

Olivier Duhart

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