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A secure, embeddable, scripting language for Java-based applications.

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# Jactl Programming Language

![logo](https://jactl.io/img/logo-picture.jpg "Jactl")

[Jactl](https://jactl.io) is a powerful scripting language for the JVM platform whose syntax is a combination of bits
from Java, Groovy, and Perl.
It can be run from a REPL and from the commandline for commandline scripts but its main goal is
to be integrated into Java applications and provide a secure, locked-down mechanism that
customers/users can use to customise the application behaviour.

It is especially suited to event-loop/reactive applications due to its built-in suspend/resume
mechanism based on continuations that ensures it never blocks the execution thread on which it is
running.

:star: Please consider giving this project a star as a way to encourage me to continue making improvements
to Jactl.

### Why Another JVM Language?

I wanted a language that was a joy to code in, was easy for Java programmers to pick up, 
provided a secure extension mechanism for applications, and was non-blocking.
Nothing I found satisfied all these needs, and so Jactl was born.

See the [FAQ](https://jactl.io/docs/faq) for a more detailed answer and answers to other questions.

## Features

### Familiar Syntax
Jactl syntax is concise and is mostly just a subset of Java and Groovy syntax with a bit of Perl thrown in for
good measure, so it is easy to pick up for anyone familiar with Java:

```groovy
int fib(int x) {
  return x <= 2 ? 1 : fib(x-1) + fib(x-2);
}
println 'fib(20) = ' + fib(20);
```

Jactl adopts a lot of Groovy syntax so semicolons are optional, typing is optional, double-quoted strings
allow for embedded expressions, and `return` is optional for the last expression of a function so the previous example
could also be written like this:

```groovy
def fib(x) { x <= 2 ? 1 : fib(x-1) + fib(x-2) }
println "fib(20) = ${fib(20)}"
```

Jactl is a multi-paradigm language and so has both Object Oriented and Functional programming features.
Here is an example showing a more functional programming approach using some built-in higher-order
functions and built-in regex support to take a file of markdown, extract the top level headings, and generate 
a table of contents:
```groovy
// Sanitise text to make suitable for a link
def linkify = { s/ /-/g;  s/[^\w-]//g }

// Find all top level headings in input and generate markdown for table of contents:
stream(nextLine).filter{ /^# /r }
                .map{ $1 if /^# (.*)/r }
                .map{ "* [$it](#${ linkify(it.toLowerCase()) })" }
                .each{ println it }
```

Another example showing Jactl's pattern matching with destructuring:
```groovy
switch (x) {
  /X=(\d+),Y=(\d+)/n -> $1 + $2    // regex match with capture vars
  [1,*]              -> 'matched'  // list whose first element is 1
  [_,_]              -> 'matched'  // list with 2 elements
  [int,String,_]     -> 'matched'  // 3 element list. 1st is an int, 2nd is a String
  [a,_,a]            -> a * 2      // 1st and last elements the same in 3 element list
  [a,*,a] if a < 10  -> a * 3      // list with at least 2 elements. 1st and last the same and < 10
  [a,${2*a},${3*a}]  -> a          // match if list is of form [2,4,6] or [3,6,9] etc
  [a,b,c,d]          -> a+b+c+d    // 4 element list
}
```

A simple quicksort:
```groovy
def qsort(x) {
  switch (x) {
    [],[_] -> x
    [h,*t] -> qsort(t.filter{it < h}) + [h] + qsort(t.filter{it >= h})
  }
}
```

See [Language Features](https://jactl.io/docs/language-features) for more language features and examples.

### Compiles to Java bytecode
Jactl scripts compile to bytecode to take advantage of the performance capabilities of the JVM.

### Supports Java 8+
Compatible with Java 8 and later versions.

### Comes with an IntelliJ Plugin
There is an IntelliJ plugin that supports syntax colouring, auto-indenting, completions, find definition/usages,
running scripts, debugging scripts, and more.
See [IntelliJ Plugin](https://github.com/jaccomoc/jactl-intellij-plugin) for more details.

### Never blocks
Jactl never blocks the execution thread on which a script is running.
This is to support execution in reactive or event loop based applications.

Blocking operations in Jactl can only occur when invoking a blocking/asynchronous function.
When executing such a function, the script will be suspended and when the blocking function completes,
the script execution state is resumed from the point at which it was suspended.
This is done via an internal _continuation_ mechanism.

Script-writers can write their code as though it blocks and do not have to be concerned about which functions are
asynchronous and which are synchronous or have to jump through the normal asynchronous programming hoops with the
use of callbacks to be invoked after a long-running operation completes.

When a blocking operation is invoked, Jactl creates a Continuation object that captures the state of the running
script such as the value of all local variables and the current call stack.
When the long-running operation completes, the script state is restored and the script continues
from where it left off.

### Checkpointing

The execution state of a script can be checkpointed when needed and this checkpointed state can be persisted or
distibuted over a network in order to recover and resume scripts after a failure.

### Extendable
Easy to integrate additional functions and methods into the language for application-specific needs.

### Secure
Unlike many other JVM based languages, in Jactl the things that a script writer can do are tightly controlled.
The only things available to the script writer are the built-in functions and the functions that you provide.
This allows Jactl scripts to be safely executed in frameworks where creating threads, writing to files,
connecting to remote systems, and performing other blocking operations would not normally be allowed.

When you integrate the Jactl compiler into your application you provide it with the functions that you want
your script writers to have access to and this ensures they can only do things that you permit them to do.
This means you don't need to worry about them accessing files or data that they shouldn't be accessing,
for example.

### No Dependencies
The core Jactl language has no dependencies on external libraries apart from the ASM library 
which it embeds within itself after renaming (to avoid clashes with any other instance of ASM
on the classpath).

### Dynamic or Static Typing
The language allows you to choose whether to specify a type for your variables, parameters,
and return types.
You can choose to provide types for stricter type checking or for optimisation reasons, or you
can leave things dynamically typed.

### Jactl REPL
Jactl has a REPL (Read-Evaluate-Print-Loop) to allow you to easily play with the language and prototype 
code at the commandline.

### Commandline Scripts
Jactl scripts can be run from the commandline to replace use of various Unix utilities such as
`awk`, `sed`, or even `Perl`.

### Language Features
* Closures
* Functional programming
  * Functions as values
  * Higher-order functions
  * Map, filter, collect, each, etc.
  * [Pattern matching with destructuring](https://jactl.io/blog/2023/12/21/switch-expressions.html)
* Classes with inheritance
* Strong/weak typing
* Parameters with default values
* Named parameters for function calls
* Multi-line strings
* Strings with interpolated expressions
* Regex matching syntax
* Regex capture variables

See [Language Features](https://jactl.io/docs/language-features) for an overview with examples of the language
features.

## Download

To run command line scripts you only need the Jactl jar which can be downloaded from Maven Central:
[https://repo1.maven.org/maven2/io/jactl/jactl/2.9.2/jactl-2.9.2.jar](https://repo1.maven.org/maven2/io/jactl/jactl/2.9.2/jactl-2.9.2.jar)

Then, to run scripts:
```shell
java -jar jactl-2.9.2.jar -e '10.map{ it + 1 }.sum()'
java -jar jactl-2.9.2.jar myscript.jactl
```

Or, you can use [JBang](https://www.jbang.dev/), if you have it installed, to run scripts.
JBang will take care of finding and downloading the JAR for you.
For example:
```shell
jbang run io.jactl:jactl:2.9.2 -e '10.map{ it + 1 }.sum()'
jbang run io.jactl:jactl:2.9.2 myscript.jactl
```

You can also download the Jactl REPL, which gives you an interactive shell for trying out Jactl code, see the
[jactl-repl](https://github.com/jaccomoc/jactl-repl) project.

Again, with JBang, running the REPL is simple to do:
```shell
$ jbang run io.jactl:jactl-repl:2.9.2
[jbang] Resolving dependencies...
[jbang]    io.jactl:jactl-repl:2.9.2
[jbang] Dependencies resolved
> 10.map{ it + 1 }.sum()
55
> :help

Available commands:
  :help          Help - print this text
  :?             Alias for :help
  :exit          Exit
  :quit          Quit - alias for :exit
  :clear         Clear current buffer
  :read file     Read and execute contents of file
  :load          Load - alias for :read
  :vars          Show variables and their values (concise form)
  :show          Show variables and their values in pretty printed form
  :purge         Purge variables and imports
  :imports       Show imports
  :java          Enable/disable Java interoperability
  :stack arg     Enable/disable stack traces for errors (true - enable, false - disable)
  :debug level   Enable/disable debug output for errors (0 - off, 1 - on, 2 - more detail)
  :history [n]   Show recent history (last n entries - defaults to 50)
  :!n            Recall history entry with given number

>
```

## Building

### Requirements

* Java 8+
* Gradle 8.0.2
* ASM 9.6

### Build

Download the source code from GitHub as a zip file or use `git` to clone the repository:
```shell
git clone https://github.com/jaccomoc/jactl.git
cd jactl
./gradlew build
```

That will build `jactl-${VERSION}.jar` under the `build/libs` directory where `${VERSION}` is the current version or
whatever version you have downloaded/checked out.

To push to your Maven repository you can use `publishToMaven`:
```shell
./gradlew build publishToMaven
```

## Integration

To use Jactl you will need to add a dependency on the Jactl library.

### Gradle

In the `dependencies` section of your `build.gradle` file:
```groovy
implementation group: 'io.jactl', name: 'jactl', version: '2.9.2'
```

### Maven

In the `dependencies` section of your `pom.xml`:
```xml
<dependency>
 <groupId>io.jactl</groupId>
 <artifactId>jactl</artifactId>
 <version>2.9.2</version>
</dependency>
```

## Learn More

The [Jactl Documentation Site](https://jactl.io) has the complete documentation including a language guide, and 
an integration guide.
It should be your first port of call.

Related GitHub projects:

* The [Jactl REPL project](https://github.com/jaccomoc/jactl-repl) provides a simple Read-Eval-Print-Loop shell for running Jactl code interactively.
* The [Jactl-Vertx library](https://github.com/jaccomoc/jactl-vertx) provides some basic Vert.x integration capabilities.

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