lieval

lieval is a lightweight Rust crate for parsing and evaluating mathematical expressions from strings.

Features

• Parse and evaluate simple mathematical expressions.
  • Basic arithmetic operations: +, -, *, /, %
  • Parentheses for expression grouping
  • Common mathematical functions: sin, cos, atan, cosh, pow, sqrt, hypot, exp, ln, div_euclid, floor etc...
  • mathematical constants such as PI, TAU, and E.
• Support for variables, operators, and functions.
• Minimal dependencies.
• Provides a simple and easy-to-use API.

Usage

Add the lieval crate to your Cargo.toml file:

[dependencies]
lieval = "<version>"

Then, in your Rust code:

use lieval::*;

assert_eq!(eval_from_str("1.0 + 2 * (3 - 1)").unwrap(), vec![5.0]);
assert_eq!(eval_from_str(&format!("1.0 + 2 * ({} - 1)", 3)).unwrap(), vec![5.0]);
assert_eq!(
    eval_from_str("1.0 - sin(3.14 / 2) * powf(1.5, 2.5)").unwrap(),
    vec![1.0 - (3.14f64 / 2.0).sin() * 1.5f64.powf(2.5)]
);

let mut expr = Expr::new("sqrt(4)").unwrap();
assert_eq!(expr.eval().unwrap(), 2.0);

// using macro `ex!`
assert_eq!(ex!("sqrt(4)").eval().unwrap(), 2.0);

You can assign numerical values to variables and evaluate them using Context.

# use lieval::*;
#
let mut context = Context::new();

assert_eq!(
    eval_from_str_with_context("1 / x", context.set_value("x", 2.0)).unwrap(),
    vec![0.5]
);
assert_eq!(
    context.eval("1 / x").unwrap(),
    0.5
);

assert_eq!(ex!("sqrt(2+x)").set_var("x", 2.0).eval().unwrap(), 2.0);
assert_eq!(ex!("sqrt(2+x+y)").set_var("x", 2.0).set_var("y", 5.0).eval().unwrap(), 3.0);

You can use custom functions.

# use lieval::*;
# 
let mut context = Context::new();

assert_eq!(
    eval_from_str_with_context("1 + func(2,3)", context.set_func("func", 2, |x| x[0] + x[1])).unwrap(),
    vec![6.0]
);
assert_eq!(
    context.eval("1 + func(2,3)").unwrap(),
    6.0
);

You can evaluate multiple expressions separated by commas or semicolons.

# use lieval::*;
# 

assert_eq!(
    eval_from_str("1 + 2, sin(3 + 0.14); 7 % 3").unwrap(), 
    vec![3.0, (3.14f64).sin(), 7.0 % 3.0]
);

let mut context = Context::new();
context.set_value("x", 3.0);
assert_eq!(context.evals("sqrt(1+x); 1+3, hypot(x,4)").unwrap(), vec![2.0, 4.0, 5.0]);

let mut expr = ex!("sqrt(1+x); 1+3, hypot(x,4)");
assert_eq!(expr.set_var("x", 3.0).evals().unwrap(), vec![2.0, 4.0, 5.0]);
assert_eq!(expr.eval().unwrap(), 2.0);
assert_eq!(expr.eval_index(2).unwrap(), 5.0);

You can efficiently evaluate by precomputing using partial_eval.

# use lieval::*;
# 
let mut expr = ex!("a1 + a2 * sin(x)");
expr.set_var("a1", 1.0)
    .set_var("a2", 0.5)
    .partial_eval()
    .unwrap();
let mut x = 1.0;
for _ in 0..10 {
    x = expr.set_var("x", x).eval().unwrap();
    assert_eq!(expr.set_var("x", x).eval().unwrap(), 1.0 + 0.5 * x.sin());
}

You can perform arithmetic operations between Expr objects.

# use lieval::*;
# 
let expr1 = Expr::new("1+x").unwrap();
assert_eq!((expr1 + ex!("2*x")).set_var("x", 2.0).eval().unwrap(), 7.0);
assert_eq!((ex!("1+x, 2+x, 3+x") + ex!("2*x, 3*x, 4*x")).set_var("x", 2.0).evals().unwrap(), vec![7.0, 10.0, 13.0]);

// broadcasting
let expr1 = Expr::new("1+x").unwrap();
let expr2 = Expr::new("2*x, 3*x, 4*x").unwrap();
assert_eq!((ex!("1+x") * ex!("2*x, 3*x, 4*x")).set_var("x", 2.0).evals().unwrap(), vec![12.0, 18.0, 24.0]);
assert_eq!((ex!("1+x") * 2.0 * ex!("x") + ex!("2*x, 3*x, 4*x") + 1.0).set_var("x", 2.0).evals().unwrap(), vec![17.0, 19.0, 21.0]);

// If variables conflict, the variable in the left expression takes precedence,
// so use partial_eval beforehand.
let mut expr1 = Expr::new("2*x").unwrap();
expr1.set_var("x", 3.0).partial_eval().unwrap();
assert_eq!((-ex!("1+x") * expr1).set_var("x", 2.0).eval().unwrap(), -18.0);

API Documentation

Detailed API documentation can be found here.

License

This project is licensed under the MIT license.