ExpressionParser

A simple lib in C# for parsing and evaluating expressions. To get it install with nuget:

Install-Package Soukoku.ExpressionParser

Supports

This lib supports most common operators.

• + addition
• - subtraction/negative
• * multiplication
• / division
• % modulus
• & bitwise and
• | bitwise or
• ! logical negation
• && logical and
• || logical or
• < less than
• <= less than or equals
• > greater than
• >= greater than or equals
• == equals
• != not equals
• ++ preincrement
• -- predecrement
• basic functions (pow, cos, sin, tan)

Usage

Create an instance of the Evaluator and call EvalueateInfix. Expressions can contain simple math or functions. The result can be retrieved with a ToString(). If an expression is not supported you will get a NotSupportedException.

var context = new EvaluationContext();
var evaluator = new Evaluator(context);
var result = evaluator.Evaluate("33 + 55");
Console.WriteLine(result.ToString()); // should be "88"

result = evaluator.Evaluate("pow(2,8)");
Console.WriteLine(result.ToString()); // should be "256"

How it works

The evaluator does its work in stages:

1. Parse input string into tokens
2. Arrange tokens into Reverse Polish notation
3. Perform the evaluation

The logical operations will result in a number with 1 being true and 0 being false.

Custom functions

The lib only comes with some built-in functions. It's possible to add your own by registering a custom routine.

var context = new EvaluationContext();

// This custom function has no parameters and always returns 5.
// The return value of a function is an ExpressToken with string value.
var myFunc = new FunctionRoutine(0, (ctx, parameters) => new ExpressionToken("5"));
context.RegisterFunction("always5", myFunc);

var evaluator = new Evaluator(context);
var result = evaluator.Evaluate("10 + always5()");
Console.WriteLine(result.ToString()); // should be "15"

Because the use of functions, floating-point numbers can only use period as the decimal separator (i.e. only "2.5" is supported, not "2,5").