Eval.cs

Mathematical expressions evaluator that supports math and enumerable functions, using only System, from the lexer to the parser with no bizarre regex.

Install

dotnet add package Eval.cs

Usage

using System;
using Eval;

// csharp prefixes can be omitted and lower cased
Console.WriteLine(Evaluator.Evaluate("-2 + pi - Ceiling(3.2)"));

// Everything is called like functions
Console.WriteLine(Evaluator.Evaluate("IEnumerable.Average(2, 3, 5)"));
Console.WriteLine(Evaluator.Evaluate("pow(-average(2, 3, 5), -5)"));
Console.WriteLine(Evaluator.Evaluate("19e-11 /- 12");
Console.WriteLine(Evaluator.Evaluate("last(4, last(1, 2), 5)");
Console.WriteLine(Evaluator.Evaluate("921.315 * -20.93 % 34.567");
Console.WriteLine(Evaluator.Evaluate(" 9>>3  /+ 1.2");

Exceptions

There are two custom exceptions, catch the rest as general exceptions that have a message

InvalidExpressionException

Means that the passed string is not a valid expression

Type	Property	Description
string	Src	the expression
int	Offset	the offset before the error, specialy useful for pointing where the error has happened
int	Length	the length of the wrong value or function
string	Message	the cause of the exception, eg: "Closing unexsistent paren"

ArgumentAmountException

Means that the wrong of arguments was passed to a function

Type	Property	Description
string	Src	same as InvalidExpressionException
int	Offset	same as InvalidExpressionException
int	Length	same as InvalidExpressionException
string	Message	the message: $"Function() expects Expected arguments but received Received"
string	Function	name of the failed function
int	Expected	expected amount of arguments
int	Received	received amount of arguments

UnexpectedEvaluationException

Should not happen unless there is a logical problem with this evaluator

Throw like an general Exception that has a message

Example

A text based exception

pow() expects 2 arguments but received 3
Math.Pow(1, 2, 3) - 4
^~~~~~~~~~~~~~~~^

using Eval;
using System;

static string ErrorMsg(string message, string src, int offset, int length)
{
    if (length < 1)
    {
        return $"{message}";
    }

    var marker = new string(' ', offset);

    if (length == 1)
    {
        marker += "^";
    }
    else if (length == 2)
    {
        marker += "^^";
    }
    else if (length > 2)
    {
        marker += $"^{new('~', length - 2)}^";
    }

    return $"{message}\n{src}\n{marker}";
}

try
{
    var result = Evaluator.Evaluate("Math.Pow(1, 2, 3) - 4");
}
catch (Exception e)
{
    Console.WriteLine(
        e switch
        {
            InvalidExpressionException ie => ErrorMsg(ie.Message, ie.Src, ie.Offset, ie.Length),
            ArgumentAmountException ae => ErrorMsg(ae.Message, ae.Src, ae.Offset, ae.Length),
            _ => e.Message
        }
    );
}

ExprGen

Generates simple math expressions, does not generate functions and parens.

EvalTest

Code to test the lexer, evaluation and exceptions.