This library provides easy to use extensible expression evaluator based on LinqyCalculator sample. The evaluator supports arithmetic operations, custom functions and parameters. It takes string representation of an expression and converts it to a structured LINQ expression instance which can easily be compiled to an executable delegate. In contrast with interpreted expression evaluators such as NCalc, compiled expressions perform just as fast as native C# methods.

var calc = new Sprache.Calc.XtensibleCalculator();

// using expressions
var expr = calc.ParseExpression("Sin(y/x)", x => 2, y => System.Math.PI);
var func = expr.Compile();
Console.WriteLine("Result = {0}", func());

// custom functions
calc.RegisterFunction("Mul", (a, b, c) => a * b * c);
expr = calc.ParseExpression("2 ^ Mul(PI, a, b)", a => 2, b => 10);
Console.WriteLine("Result = {0}", expr.Compile()());

// end-user's functions
calc.RegisterFunction("Add", "a + b", "a", "b");
expr = calc.ParseExpression("Add(353, 181)");
Console.WriteLine("Result = {0}", expr.Compile()());

To use expression evaluator in your projects, install Sprache.Calc NuGet package by running the following command in the Package Manager Console:

PM> Install-Package Sprache.Calc

Sprache.Calc library serves as a demonstration of grammar inheritance technique with Sprache toolkit. An article describing Sprache.Calc implementation details is currently available in English and Russian:

• Sprache.Calc: building yet another expression evaluator
• Наследование грамматик в Sprache на примере калькулятора выражений.

TL;DR:

• Declare parsers as virtual properties instead of static fields
• Decompose the grammar into small and reusable rules
• Write unit tests for every single atomic parser
• Use "protected internal" access modifier to enable unit testing
• Unit tests must be organized in the same hierarchy as parser classes