默认函数

使用 Functions::default; 访问

• log(底数,值)
• sqrt(值)
• sin(值)
• cos(值)
• tan(值)

自定义错误系统

• 公开了 Error 枚举，允许用户确定发生了哪种类型的错误，并获取有关它的所有相关信息
• 如果需要，允许用户自行处理错误，也可以直接打印出来。

示例

整数方程

// evaluates an algebraic equation
use calc_lib::evaluate;

fn main() {
    // the equation to evaluate
    let eval = evaluate("1 + 2 * 3");
    // print out errors if they occur, or handle them another way
    if eval.is_err() {
        panic!("{}", eval.err().unwrap());
    }
    // the result is a f64, which can then be used as needed
    // here, I am just asserting that it is the value it should be.
    assert_eq!(eval.unwrap() as i32, 7);
}

小数方程

use calc_lib::evaluate;

fn main() {
    // define the expression
    let expression = "1.3 + 2.5 * 3.1";
    // evaluate the expression
    let eval = evaluate(expression);
    // handle errors that may occur
    if eval.is_err() {
        panic!("{}", x.unwrap_err());
    }
    assert_eq!(eval.unwrap(), 9.05);
}

用变量求解

use calc_lib::{evaluate_with_defined, Definitions, Functions, Error};

fn main() {
    // define x as 16
    let mut defs = Definitions::new();
    defs.register("x", 16);
  
    // create the functions list
    // this defines an empty Functions struct with no functions.
    // for functions like log, sqrt, sin, cos, tan, etc., use `Functions::default()`
    let mut funcs = Functions::new();
    // this shows the definition of the log function,
    // exactly how it is implemented in `Functions::default();`
    funcs.register("log", |args| {
        // args is of type Vec<f64>
        // this takes 2 arguments: base, number
        if args.len() != 2 {
            return Err(Error::arg_count("log", 2, args.len()));
        }
        // return the value
        Ok(args[1].log(args[0]))
    });
    // evaluate the expression and verify the results
    let eval = evaluate_with_defined("log(2, x)", Some(&defs), Some(&funcs));
    if eval.is_err() { 
      panic!("{}", eval.unwrap_err());
    }
    assert_eq!(eval.unwrap(), 4.0);
}