evalexpr

Evalexpr is a powerful arithmetic and boolean expression evaluator.

Documentation

Quickstart

Add evalexpr as dependency to your Cargo.toml:

[dependencies]
evalexpr = "0.5"

Add the extern crate definition to your main.rs or lib.rs:

extern crate evalexpr;

Then you can use evalexpr to evaluate expressions like this:

use evalexpr::*;

assert_eq!(eval("1 + 2 + 3"), Ok(Value::from(6)));
assert_eq!(eval("1 - 2 * 3"), Ok(Value::from(-5)));
assert_eq!(eval("1.0 + 2 * 3"), Ok(Value::from(7.0)));
assert_eq!(eval("true && 4 > 2"), Ok(Value::from(true)));

And you can use variables and functions in expressions like this:

use evalexpr::*;

let mut configuration = HashMapConfiguration::new();
configuration.insert_variable("five", 5);
configuration.insert_variable("twelve", 12);
configuration.insert_function("f", Function::new(1 /* argument amount */, Box::new(|arguments| {
    if let Value::Int(int) = arguments[0] {
        Ok(Value::Int(int / 2))
    } else if let Value::Float(float) = arguments[0] {
        Ok(Value::Float(float / 2.0))
    } else {
        Err(Error::expected_number(arguments[0].clone()))
    }
})));

assert_eq!(eval_with_configuration("five + 8 > f(twelve)", &configuration), Ok(Value::from(true)));

You can also precompile expressions like this:

use evalexpr::*;

let precompiled = build_operator_tree("a * b - c > 5").unwrap();

let mut configuration = HashMapConfiguration::new();
configuration.insert_variable("a", 6);
configuration.insert_variable("b", 2);
configuration.insert_variable("c", 3);
assert_eq!(precompiled.eval(&configuration), Ok(Value::from(true)));

configuration.insert_variable("c", 8);
assert_eq!(precompiled.eval(&configuration), Ok(Value::from(false)));

Features

Operators

Supported binary operators:

Operator	Precedence	Description		Operator	Precedence	Description
+	95	Sum		<	80	Lower than
-	95	Difference		>	80	Greater than
*	100	Product		<=	80	Lower than or equal
/	100	Division		>=	80	Greater than or equal
%	100	Modulo		==	80	Equal
&&	75	Logical and		!=	80	Not equal
||	70	Logical or

Supported unary operators:

Operator	Precedence	Description
-	110	Negation
!	110	Logical not

Values

Operators take values as arguments and produce values as results. Values can be boolean, integer or floating point numbers. Strings are supported as well, but there are no operations defined for them yet. Values are denoted as displayed in the following table.

Value type	Example
Value::Boolean	true, false
Value::Int	3, -9, 0, 135412
Value::Float	3., .35, 1.00, 0.5, 123.554

Integers are internally represented as i64, and floating point numbers are represented as f64. Operators that take numbers as arguments can either take integers or floating point numbers. If one of the arguments is a floating point number, all others are converted to floating point numbers as well, and the resulting value is a floating point number as well. Otherwise, the result is an integer.

Variables

This crate allows to compile parameterizable formulas by using variables. A variable is a literal in the formula, that does not contain whitespace or can be parsed as value. The user needs to provide bindings to the variables for evaluation. This is done with the Configuration trait. Two structs implementing this trait are predefined. There is EmptyConfiguration, that returns None for each request, and HashMapConfiguration, that stores mappings from literals to variables in a hash map.

Variables do not have fixed types in the expression itself, but aer typed by the configuration. The Configuration trait contains a function that takes a string literal and returns a Value enum. The variant of this enum decides the type on evaluation.

Functions

This crate also allows to define arbitrary functions to be used in parsed expressions. A function is defined as a Function instance. It contains two properties, the argument_amount and the function. The function is a boxed Fn(&[Value]) -> Result<Value, Error>. The argument_amount is verified on execution by the crate and does not need to be verified by the function. It determines the length of the slice that is passed to function. See the examples section above for examples on how to construct a function instance.

License

This crate is primarily distributed under the terms of the MIT license. See LICENSE for details.