Crate eval

Eval is a powerful expression evaluator.

Supported operators: ! != "" '' () [] . , > < >= <= == + - * / % && || n..m.

Built-in functions: min() max() len() is_empty() array().

Examples

You can do mathematical calculations with supported operators:

use eval::{eval, to_value};

assert_eq!(eval("1 + 2 + 3"), Ok(to_value(6)));
assert_eq!(eval("2 * 2 + 3"), Ok(to_value(7)));
assert_eq!(eval("2 / 2 + 3"), Ok(to_value(4.0)));
assert_eq!(eval("2 / 2 + 3 / 3"), Ok(to_value(2.0)));

You can eval with context:

use eval::{Expr, to_value};

assert_eq!(Expr::new("foo == bar")
               .value("foo", true)
               .value("bar", true)
               .exec(),
           Ok(to_value(true)));

You can access data like javascript by using . and []. [] supports expression.

use eval::{Expr, to_value};
use std::collections::HashMap;

let mut object = HashMap::new();
object.insert("foos", vec!["Hello", "world", "!"]);

assert_eq!(Expr::new("object.foos[2-1] == 'world'") // Access field `foos` and index `2-1`
               .value("object", object)
               .exec(),
           Ok(to_value(true)));

You can eval with function:

use eval::{Expr, to_value};

assert_eq!(Expr::new("say_hello()")
               .function("say_hello", |_| Ok(to_value("Hello world!")))
               .exec(),
           Ok(to_value("Hello world!")));

You can create an array with array():

use eval::{eval, to_value};

assert_eq!(eval("array(1, 2, 3, 4, 5)"), Ok(to_value(vec![1, 2, 3, 4, 5])));

You can create an integer array with n..m:

use eval::{eval, to_value};

assert_eq!(eval("0..5"), Ok(to_value(vec![0, 1, 2, 3, 4])));

Built-in functions

min()

Accept multiple arguments and return the minimum value.

max()

Accept multiple arguments and return the maximum value.

len()

Accept single arguments and return the length of value. Only accept String, Array, Object and Null.

is_empty()

Accept single arguments and return a boolean. Check whether the value is empty or not.

array()

Accept multiple arguments and return an array.

Structs

ExecOptions	Execute options
Expr	Expression builder
Function	Custom function

Enums

Error	Expression parsing error
Value	Represents any valid JSON value.

Functions

eval	Evaluates the value of an expression.
to_value	Convert variable to serde_json::Value

Type Definitions

Context	Custom context.
Contexts	Custom contexts. The value of the last context is searched first.
Functions	Custom functions.