eqeval

eqeval converts equations strings to their respective value using the finum crate. We therefore avoid any floating-point errors and are entirely reliant on the precision values provided by the finum crate.

Usage

Add this to your Cargo.toml:

[dependencies]

eqeval = "0.2.0"

Creating custom variables

Creating custom variables is done via the Variable struct. To create an instance of this struct you need:

a name
the value (as a FiLong)

Creating custom functions

In order to create a custom function for the equation evaluator, you have use the Function struct. Each function needs:

a name
the actual function (parameters: vector of FiLong; output type: FiLong)
a special value (this value, usually 0, can provide additional context e. g. trigonometric functions)

Special Value	Function
0	Base case; no special handeling
1	For trig. function with parameters given in degrees
2	For trig. function that return a value in degrees

Potential Issues

Make sure your custom functions do not include rad_to_deg/deg_to_rad in its entirety in the name
Functions musn't include any of the following symbols: #, +, -, *, /, ^, @, !, ? (I did not include a check for that; if you're actually trying to use a operand's symbol in a function name that on you)

Your first equation

Generally parsing equations is done by using the eval! macro. You can choose to provide additional context in form of the deg boolean or one/both of the two context vectors for variables and functions.

How to write an equation

The Equation must always be provided as a String. These are the symbols for the operands:

Symbol	Function	Example
+	Addition	2 + 4 → 6
-	Subtraction or Negative Value	7 - 3 → 4 or -5 → -5
*	Multiplication	12 * 4 → 48
/	Division	39 / 13 → 13
^	Exponentiation	2 ^ 8 → 256
@	Logarithm	81 @ 3 → ${\log_3 81}$ → 4
!	Factorial	3! → 1 * 2 * 3 → 6
?	Termial	6? → 1 + 2 + 3 + 4 + 5 + 6 → 21

Generally there's no limit in equation size (aside from String limits in rust) or in context provided but it'll run faster for smaller equations/fewer context added

How equations get parsed

The general Order of Operations: (lower number → parsed earlier):

parenthesis
functions (sin, abs)
exponentiation/logarithm
factorials/termials
modulu
multiplication/division
addition/subtraction

An Example Equation

This is an example equation with variables as context:

fn main() {
    let mut context: Vec<Variable> = Vec::new();
    context.push(Variable{name: String::from("re"), val: FiLong::two()});
    context.push(Variable{name: String::from("pl"), val: FiLong::six()});
    println!("{}", eval!("re! + (9^0.35) * 1^2!@8 - (4 + 5(3sin(0.213) - 9)) * abs(2.23) + pl? + 7.0cos(-31.9)(3)!^2", vars: context));
}

The result should be: 330.40574755336320971885

eqeval 0.2.0