expressive/README.md

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eval
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====
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[![Project Status: Active - The project has reached a stable, usable state and is being actively developed.](http://www.repostatus.org/badges/latest/active.svg)](http://www.repostatus.org/#active)
[![docs](https://docs.rs/eval/badge.svg?version=0.4.0 "docs")](https://docs.rs/eval)
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Eval is a powerful expression evaluator.
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[Document](https://docs.rs/eval)
--------------------------------
Features
--------
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Supported operators: `!` `!=` `""` `''` `()` `[]` `,` `>` `<` `>=` `<=` `==`
`+` `-` `*` `/` `%` `&&` `||` `n..m`.
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Built-in functions: `min()` `max()` `len()` `is_empty()` `array()`.
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Where can eval be used?
-----------------------
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* Template engine
* ...
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Usage
-----
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Add dependency to Cargo.toml
```toml
[dependencies]
eval = "^0.4"
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```
In your `main.rs` or `lib.rs`:
```rust
extern crate eval;
```
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Examples
--------
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You can do mathematical calculations with supported operators:
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```rust
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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:
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```rust
use eval::{Expr, to_value};
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assert_eq!(Expr::new("foo == bar")
.value("foo", true)
.value("bar", true)
.exec(),
Ok(to_value(true)));
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```
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You can access data like javascript by using `.` and `[]`. `[]` supports expression.
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```rust
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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[1-1] == 'Hello'")
.value("object", object)
.exec(),
Ok(to_value(true)));
```
You can eval with function:
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```rust
use eval::{Expr, to_value};
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assert_eq!(Expr::new("say_hello()")
.function("say_hello", |_| Ok(to_value("Hello world!")))
.exec(),
Ok(to_value("Hello world!")));
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```
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You can create an array with `array()`:
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```rust
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use eval::{eval, to_value};
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assert_eq!(eval("array(1, 2, 3, 4, 5)"), Ok(to_value(vec![1, 2, 3, 4, 5])));
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```
You can create an integer array with `n..m`:
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```rust
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use eval::{eval, to_value};
assert_eq!(eval("0..5"), Ok(to_value(vec![0, 1, 2, 3, 4])));
```
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License
-------
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eval is primarily distributed under the terms of the MIT license.
See [LICENSE](LICENSE) for details.