ExpressionEvaluator is a .NET library for evaluating string expressions using binary expression trees or reverse polish notation.

The ExpressionEvaluator.Abstractions project contains the core abstractions and interfaces used by the library. Two of the most important interfaces are IStringArrayExpressionEvaluator and IStringExpressionEvaluator.

IStringArrayExpressionEvaluator was previously described as an interface for evaluating mathematical expressions represented as arrays of strings. The method defined in this interface takes an iterator object "words" as input, which represents a tokenized expression. For example, the input ["1","+","2"] represents the expression "1 + 2".

IStringExpressionEvaluator is another interface that defines a string Evaluate(string expression) method. This method takes a string expression and evaluates it, returning the result as a string. This interface can be useful for evaluating simpler expressions that do not require tokenization or for cases where the expression is already provided in string format.

Together, these two interfaces provide a flexible and modular approach to evaluating mathematical expressions, accommodating different formats of expressions and allowing for easy implementation of custom evaluators.

The ExpressionEvaluator.BET project contains an implementation of the expression evaluator using binary expression trees.

The ExpressionEvaluator.RPN project contains an implementation of the expression evaluator using reverse polish notation.

The ExpressionEvaluator.Calculator project contains a calculator implementation for evaluating arithmetic expressions.

The ExpressionEvaluator.RegexTokenizer project contains an implementation of a tokenizer using regular expressions.

The ExpressionEvaluator.Utilities project contains utility classes and methods used by the library.

The ExpressionEvaluator.Default.BET and ExpressionEvaluator.Default.RPN projects provide quick registration of the ExpressionEvaluator to the dependency injection container.

To get started, add the ExpressionEvaluator to your IServiceCollection and use the IStringExpressionEvaluator to evaluate expressions:

var services = new ServiceCollection();
services.AddDefaultBETExpressionEvaluator();
var provider = services.BuildServiceProvider();
var expressions = new string[] { /* list of expressions to evaluate */ };
var expressionEvaluator = provider.GetService<IStringExpressionEvaluator>();

foreach (var expression in expressions)
{
    Console.WriteLine($"{expression} = {expressionEvaluator.Evaluate(expression)}");
}

ExpressionEvaluator provides customization options to allow users to add their own functionality to the library.

Users can implement their own tokenizer by implementing the ITokenizer interface and registering it with the IExpressionEvaluatorBuilder using the AddCustomTokenizer method.

For example, a custom tokenizer that splits expressions into words separated by underscores could be implemented as follows:

public class UnderscoreTokenizer : ITokenizer
{
    public IEnumerable<string> Tokenize(string expression)
    {
        return expression.Split('_');
    }
}

And registered using:

services.AddExpressionEvaluatorCore()
    .AddCustomTokenizer<UnderscoreTokenizer>();

ExpressionEvaluator provides interfaces to implement custom evaluators for both single string expressions and arrays of string expressions.

Users can implement their own single string expression evaluators by implementing the IStringExpressionEvaluator interface and registering it with the IExpressionEvaluatorBuilder using the AddCustomExpressionStringEvaluator method.

For example, a custom evaluator that evaluates expressions as JavaScript code could be implemented as follows:

public class JavaScriptEvaluator : IStringExpressionEvaluator
{
    public string Evaluate(string expression)
    {
        // evaluate expression as JavaScript code
        return JavaScriptEngine.Evaluate(expression).ToString();
    }
}

And registered using:

services.AddExpressionEvaluatorCore()
    .AddCustomExpressionStringEvaluator<JavaScriptEvaluator>();

Contributions to this project are welcome. Please submit pull requests or issues to the GitHub repository.

License This project is licensed under the MIT License.