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.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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