Simple application example of rhai script engine

In the last article , A brief introduction Rhai Role and function of script engine , See Rhai - Rust Embedded script engine .

In this article, we start with the simplest string Application , Let's see Rhai How easy it is to write scripts . Mainly from three application points ： stay Rust Call embedded Rhai Script ; independent Rhai Script ;web In terms of development , Combined template engine , call Rhai Script , Render the template .

• stay Rust Call embedded Rhai Script

First , We will be having Cargo.toml Add dependencies in ：

[dependencies]
rhai = "0.19.10"

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then , stay Rust In the code , So we can do some research on the embedded Rhai Script for calculation . The example is to calculate the number in the string

use rhai::{Engine, EvalAltResult, INT};

fn main() -> Result<(), Box<EvalAltResult>> {
    let engine = Engine::new();

    let result = engine.eval::<INT>("40 + 2")?;

    println!(" The result of the calculation is ：{}", result); //  Will print  42

    Ok(())
}

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The result of the calculation can be passed on to others Rust Code 、Rhai Script , And others Python Script 、web Front end, etc , and Rust The code is basically the same .

• independent Rhai Script

The following example is pure Rhai Script example , It is also string processing , Please note that Rhai As no-std Of Rust The script engine , Introduces the dynamic type , So it's written with Rust The code is very similar , But it's easier ： Easy to write 、 Easy to read .

//  This script tests string operations 

print(" Hello! ！");                //  Be careful  Rust  In the code , Use macros  print!  or  println!
print(" such \n very  \\  Great ！");     //  Embed newline 
print("40 16  Into the system for ：\x40");     //  Convert to  16  Base number 
print("unicode：\u2764");       // Unicode
print("unicode：\U0001F603");   // Unicode
print(" Chengdu " + "->" + " sanya ");     //  Use strings to build strings 
print("foo" < "bar");           //  String comparison ,Rhai  Only support  ==、<、>  etc. 
print(" you " >= " you ");          //  String comparison ,Rhai  China does not support it.  eq、lt、gt  etc. 
print(" The output is ：" + 42);   //  Use a string of non string type to build 

let s = "\u2764 hello, world! \U0001F603"; //  String variable 
print(" length =" + s.len);       //  The result is printed as  17

s[s.len-3] = '?';               //  Modify string 
print(" Change the result to ：" + s);        //  Will print  ' Change the result to ：hello, world?'

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• Combined template engine , call Rhai Script , Render the template

The following example is in support of Rhai Script parsing （ Template dependency crate contain Rhai） In the template engine of , Use independent Rhai Script for rendering assistance .

First , In response to the template handler in , We need to register the script assistant , You can register multiple . We register for the following example 2 individual , The template rendering is processed separately according to the user's personal site category , Show the corresponding site svg, And handle the user blog name ：

pub async fn user_index(req: Request<State>) -> tide::Result {
    let mut user_tpl: Tpl = Tpl::new("users/index").await;
    user_tpl.reg.register_script_helper_file(
        "website-svg",
        format!("{}{}", rhai_dir().await, "website-svg.rhai"),
    )?;
    user_tpl.reg.register_script_helper_file(
        "blog-name",
        format!("{}{}", rhai_dir().await, "blog-name.rhai"),
    )?;
    ...
    ...

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then , independent Rhai Script website-svg.rhai by ：

let website = params[0];
let is_github = website.contains("github.com");

if is_github {
    "M8 0C3.58 0 0 3.58 0 ..."
} else {
    "M6.5 14.5v-3.505c0-...."
}

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Script blog-name.rhai We have omitted .

Last , In the template file （ namely html、jinja2、hbs etc. ） in , We use a method similar to variable parsing to call ：

<div class="col-4 text-center">
  <a class="blog-header-logo text-dark" href="{{ user.website }}" target="_blank">
    {{ blog-name user.blogName }}
    <svg width="28" height="28" viewBox="0 0 18 18" fill="currentColor">
      <path d="{{ website-svg user.website }}" />
    </svg>
  </a>
</div>

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When rendering the template on the server , Template engine built-in rhai rely on crate Will be right rahi Script for calculation . And the first one in the text rhai Application way ——Rust Embed... In the code Rhai Script —— similar .

Application examples through three ways , We can find out ：Rhai In terms of overall application scope , At present, it is still very narrow . also Besides the excellent performance , Other advantages are not particularly obvious .

Most of the experimenters are based on Rust Trust in language performance , So as to simplify the complex problems . For example, the author's current application , It also focuses on template rendering assistance .

For applications where performance is especially important ,Rhai The scripting engine is a very interesting one to consider . For other considerations , The technology stack will also have an option . Interested friends can visit the website ：https://rhai.budshome.com, For a detailed understanding .