Crate resolver

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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 resolver::{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 resolver::{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 resolver::{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 resolver::{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 resolver::{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 resolver::{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

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