Prexel

An evaluator for math expressions.

Usage

[dependencies]
prexel = "0.1.0"

Examples

You can use Evaluator<N> for evaluate an expression.

fn main(){
    let evaluator: Evaluator<f64> = Evaluator::new();
    println!("{:?}", evaluator.eval("2 + 3 * 5"));
}

Warning

This library is not stable and could have breaking changes in any time.

Implementation

There are 3 steps for evaluating each expression:

• Tokenization: A string is converted into an array of tokens.

• Conversion: The array of tokens is converted from infix to postfix notation using the Shunting Yard Algorithm.

• Evaluation: The resulting RPN (Reverse Polish Notation) expression is evaluated.

This is done using the Tokenizer, Evaluator and Context. The Tokenizer converts an str to Tokens and the Evaluator process and evaluates the tokens.

The Context is where all the functions, variables, constants and additional information used for evaluation is stored. You can use the implementation provided by DefaultContext.

Precision

Some math functions implemented in prexel::ops::math like trigonometric functions use internally f64 for the calculations using the traits FromPrimitive and ToPrimitive what may lead to precision errors.

If you need higher precision make use of the decimal feature to enable a 128 bits decimal number:

use prexel::context::DefaultContext;
use prexel::evaluator::Evaluator;

fn main(){
    let context = DefaultContext::new_decimal();
    let evaluator = Evaluator::with_context(context);

    println!("{:?}", evaluator.eval("Cos(180) * 10!"));
}