Crate mexe

mathematical expression evaluator.

How to Use

use mexe::eval;

fn main() {
    let forty_six = eval("(5 * 8) + 6").unwrap();
    let two = eval("1 + 1").unwrap();
    println!("{} & {}", forty_six, two);

    assert_eq!(forty_six, 46.0);
    assert_eq!(two, 2.0);
}

Note: the above assert_eqs work, but for float comparison in general use a crate such as float-cmp.

Why?

If you need to evaluate simple arithmetic expressions, this crate offers a fast and lightweight solution.

In our current benchmarks, it’s about 4-10x faster than meval, about 2x faster than fasteval, and the fully-featured evalexpr is generally the slowest. Note that those crates do much more than mexe – especially evalexpr. Our focus on a very small problem makes it easier for us to ship a fast and lean library.

Includes

• sum
• subtraction
• multiplication
• division
• integers
• floats
• parentheses
• arbitrary whitespace

Goals

• Minimal
• Fast: O(n)
• No allocations if possible
• We can assume the input is ASCII, and throw an error otherwise
• Thoroughly tested
• Maybe try to make it no-std

Grammar

See readme.

Grammar idea adapted from this post.

Our first implementation uses an LL(1) parser.

Similar Projects

• evalexpr
• meval
• fasteval
• pmalmgren/rust-calculator
• adriaN/simple_rust_parser

Links

• Documentation: docs.rs
• Crate: crates.io and lib.rs
• Repository: Github

Enums

MexeError

Represents any errors that may occur in this library

Functions

eval

Evaluates a numeric expression.

eval_binaryDeprecated

Evaluates a numeric expression assuming it is just one operation between two numbers, without parentheses. Whitespace is ignored. Floating point numbers must be represented in the X.Y form, where X and Y are non-empty sequence of digits. The notation with the exponent is not currently supported.

Type Definitions

Result

Represents the result of any fallible operation in this library