Math Expression Parser

This parser was written entirely in C#, and was created for the sake of learning about Abstract Syntax Trees, Recursive Descent Parsing, and the Visitor Pattern.

Contributions, suggestions, and critiques are greatly appreciated!

Currently Supported Features

Expressions

>>> 2 / 2
1
>>> 5! * 5
600
>>> -(8!) + 9 ^ 3
-39591
>>> pi ^ 2
9.869604401089358

Constants

>>> pi
3.141592653589793
>>> e
2.718281828459045

Function Calls

>>> sin(0)
0
>>> factorial(5)
120
>>> tan(0)
0

Side note: trigonometric functions take radians, not degrees.

Modifying the internal math library

You are able to create your own constants and functions by modifying the MathLibrary class.

Functions are created by annotating them with the FunctionName annotation, and constants are created by annotating them with the MathConstant annotation. For example,

public class MathLibrary
{
	/*
	 * The first parameter is the name the user
	 * will need to use. Fairly self-explanatory.
	 */
	[MathConstant("myConstant")]
	private static readonly double MyConstant = 1234.5;

	/*
	 * The first parameter of the constructor
	 * is the name the user will call the function with.
	 * Note: The user can call the function in ANY casing
	 * and it will work.
	 * 
	 * The second parameter is optional,
	 * and indicates how many arguments the function takes.
	 * 
	 * If left out, the function will take as many arguments
	 * as the user enters.
	 */
	[FunctionName("myFunction", 1)]
	public static double DoSomething(double input)
	{
		return input + 1;
	}

	// When the argument number param is left out, the input is passed in as an array.
	[FunctionName("anotherFunction")]
	public static double AnotherFunction(double[] input)
	{
		double sum = 0;
		foreach(var number in input)
		{
			sum += number;
		}
		
		return sum;
	}
}

Issues/To-do list

• Support postfix unary operators.
• Support more accurate trig function calls. Floating point inaccuracies mess with some values, such as asymptotes.
• Use source generators instead of reflection for functions/constants.
• Perhaps support variable declarations?
• More tests.

This project has been largely inspired by Crafting Interpreters, check out the book if you're interested in creating an interpreter or compiler of your own!