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)"), Ok(vec![5.0]));
assert_eq!(
    eval_from_str("1.0 - sin(3.14 / 2) * powf(1.5, 2.5)"),
    Ok(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(), Ok(2.0));

// using macro `ex!`
assert_eq!(ex!("sqrt(4)").eval(), Ok(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)),
    Ok(vec![0.5])
);

assert_eq!(ex!("sqrt(2+x)").set_var("x", 2.0).eval(), Ok(2.0));
assert_eq!(ex!("sqrt(2+x+y)").set_var("x", 2.0).set_var("y", 5.0).eval(), Ok(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])),
    Ok(vec![6.0])
);
assert_eq!(
    ex!("1 + func(x)").set_func("func", 1, |x| x[0] * 2.0).set_var("x", 1.0).eval(),
    Ok(3.0)
);

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"), 
    Ok(vec![3.0, (3.14f64).sin(), 7.0 % 3.0])
);

let mut expr = ex!("sqrt(1+x); 1+3, hypot(x,4)");
assert_eq!(expr.set_var("x", 3.0).evals(), Ok(vec![2.0, 4.0, 5.0]));
assert_eq!(expr.eval(), Ok(2.0));
assert_eq!(expr.eval_index(2), Ok(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(), Ok(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(), Ok(7.0));
assert_eq!((ex!("1+x, 2+x, 3+x") + ex!("2*x, 3*x, 4*x")).set_var("x", 2.0).evals(), Ok(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(), Ok(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(), Ok(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(), Ok(-18.0));

API Documentation

Detailed API documentation can be found here.

License

This project is licensed under the MIT license.