Function evaluate 

pub fn evaluate(raw_expression: &str) -> Result<f64, String>

Evaluate a mathematical expression.

If error occurs during evaluation, an error message is stored in string contained in Result output. Otherwise, the Result output contains the value of evaluation stored in 64-bits float.

Example of simple expression

use taz;

let expression: String = String::from("2.0 * (4.43 - 5.99) / 3.0");

let result: Result<f64, String> = taz::evaluate(expression.as_str());
assert!(result.is_ok());

match result {
    Ok(value) => println!("{expression} = {value}"),
    Err(message) => println!("Error occured: {message}")
}

Example of expression containing predefined constants and function

use taz;

let expression: String = String::from("cos(pi / 4.0)^2 + sin(pi / 4.0)^2");

let result: Result<f64, String> = taz::evaluate(expression.as_str());
assert!(result.is_ok());

match result {
    Ok(value) => println!("{expression} = {value}"),
    Err(message) => println!("Error occured: {message}")
}