mexe version 0.0.2

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);
}

Why?

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

It's about 4-10x faster than meval and about 2x faster than fasteval, but there are still optimisations to come, which will make it even faster. Note that those crates do much more than mexe. 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
Having fun

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Grammar

E  -> T E'
E' -> + T E'
E' -> - T E'
E' -> ε
T  -> F T'
T' -> * F T'
T' -> / F T'
T' -> ε
F  -> ( E )
F  -> n
F  -> - ( E )
F  -> - n

where ε is the empty string and n is a terminal number token. Grammar idea adapted from this post.