J* is a dynamic embeddable scripting language designed to be as easy as possible to embed into
another program. It arises from the need of having a modern scripting language with built-in
support for OOP whilst mantaning simplicity of use and a low memory footprint. It can be viewed as
a middle ground between Python, a more complete scripting language with lots of features and
libraries, and LUA, a small and compact language that is simple to embed but doesn't provide OOP
functionalities out of the box.
J* tries to take the best of both worlds, implementing a fully featured class system while
maintaining a small standard library and employing the use of a stack based API for communication
among the language and host program, rendering embedding simple.
J* is:
- Small. The implementation spans only a handful of files and the memory footprint is low thanks to a minimal standard library that provides only essential functionalities.
- Easy to use. The API is contained in a single header file and employs a stack based approach similar to the one of LUA, freeing the user from the burden of keeping track of memory owned by the language.
- Fully object oriented. Every entity, from numbers to class instances, is an object in J*
- Modular. A fully fledged module system makes it easy to split your code across multiple files
- Easily extensible. The language can be easily extended by creating C functions callable from J* using the API, or by importing C extensions provided as dynamic libraries.
To get a feel of the language, try it in your browser!
Besides the language implementation, a simple executable called jstar is provided to start using
the language without embedding it into another program.
If the jstar binary is executed without
arguments it behaves like your usual read-eval-print loop, accepting a line at a time and executing
it:
J*>> var helloWorld = 'Hello, World!'
J*>> print(helloWorld)
Hello, World!
J*>> _You can even write multiline code, it will look like this:
J*>> for var i = 0; i < 3; i += 1 do
.... print('Hello, World!')
.... end
Hello, World!
Hello, World!
Hello, World!
J*>> _When you eventually get bored, simply press Ctrl+d or Ctrl+c to exit the interpreter.
If you instead want to execute code written in some file, you can pass it as an argument to jstar
and it will be executed. Passing more than one argument causes all but the first to be forwarded to
the language as script arguments. You can then read them from the script this way:
if #argv > 0 then
print('First argument: ', argv[0])
else
raise Exception('No args provided')
endThe jstar executable can also accept various options that modify the behaviour of the command line
app. To see all of them alongside a description, simply pass the -h option to the executable.
In addition to being a useful tool to directly use the programming language, the command line app is also a good starting point to learn how J* can be embedded in a program, as it uses the API to implement all of its functionalities. You can find the code in cli/src/cli.c.
Precompiled binaries are provided for Windows and Linux for every major release. You can find them here.
The J* library requires a C99 compiler and CMake (>= 3.9) to be built, and is known to compile on OSX (Apple clang), Windows (both MSVC and MinGW-w64) and Linux (GCC, clang).
To build the provided command line app jstar, a C++11 compiler is required as one of its
dependencies, linenoise-ng, is written in C++.
Additionally, if one wishes to modify the standard library (.jsr files in jstar/src/builtin), a python interpreter (version >= 3) is required to generate header files from the code (CMake will automatically take care of this).
You can clone the latest J* sources using git:
git clone https://github.com/bamless/jstar.git
After cloning, use cmake to generate build files for your build system of choice and build the
target libjstar/libjstar_static if you only want to generate the language dynamic/static library
, or the all target if you want to build both the library and the command line app. On UNIX
systems this can be simply achieved by entering this in the command line:
cd jstar; mkdir build; cd build; cmake ..; make -j
Various CMake options are available to switch on or off certain functionalities:
| Option name | Default | Description |
|---|---|---|
| JSTAR_NAN_TAGGING | ON | Use the NaN tagging technique for storing the VM internal type. Decrases the memory footprint of the interpreter and increases speed |
| JSTAR_COMPUTED_GOTOS | ON | Use computed gotos to implement the VM eval loop. Branch predictor friendly, increases performance. Not all compilers support computed gotos (MSVC for example), so if you're using one of them disable this option |
| JSTAR_INSTALL | ON | Generate install targets for the chosen build system. Turn this off if including J* from another CMake project |
| JSTAR_SYS | ON | Include the 'sys' module in the language |
| JSTAR_IO | ON | Include the 'io' module in the language |
| JSTAR_MATH | ON | Include the 'math' module in the language |
| JSTAR_DEBUG | ON | Include the 'debug' module in the language |
| JSTAR_RE | ON | Include the 're' module in the language |
| JSTAR_DBG_PRINT_EXEC | OFF | Trace the execution of instructions of the virtual machine |
| JSTAR_DBG_STRESS_GC | OFF | Stress the garbage collector by calling it on every allocation |
| JSTAR_DBG_PRINT_GC | OFF | Trace the execution of the garbage collector |