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**Janet** is a functional and imperative programming language and bytecode interpreter. It is a
modern lisp, but lists are replaced
by other data structures with better utility and performance (arrays, tables, structs, tuples).
The language also supports bridging to native code written in C, meta-programming with macros, and bytecode assembly.
There is a repl for trying out the language, as well as the ability
to run script files. This client program is separate from the core runtime, so
janet could be embedded into other programs. Try janet in your browser at
[https://janet-lang.org](https://janet-lang.org).
## Use Cases
Janet makes a good system scripting language, or a language to embed in other programs. Think Lua or Guile.
## Features
* Minimal setup - one binary and you are good to go!
* First class closures
* Garbage collection
* First class green threads (continuations)
* Python style generators (implemented as a plain macro)
* Mutable and immutable arrays (array/tuple)
* Mutable and immutable hashtables (table/struct)
* Mutable and immutable strings (buffer/string)
* Lisp Macros
* Byte code interpreter with an assembly interface, as well as bytecode verification
* Tailcall Optimization
* Direct interop with C via abstract types and C functions
* Dynamically load C libraries
* Functional and imperative standard library
* Lexical scoping
* Imperative programming as well as functional
* REPL
* Parsing Expression Grammars built in to the core library
* 300+ functions and macros in the core library
* Embedding Janet in other programs
* Interactive environment with detailed stack traces
## Documentation
* For a quick tutorial, see [the introduction](https://janet-lang.org/docs/index.html) for more details.
* For the full API for all functions in the core library, see [the core API doc](https://janet-lang.org/api/index.html)
Documentation is also available locally in the repl.
Use the `(doc symbol-name)` macro to get API
documentation for symbols in the core library. For example,
```
(doc doc)
```
Shows documentation for the doc macro.
To get a list of all bindings in the default
environment, use the `(all-symbols)` function.
## Source
You can get the source on [GitHub](https://github.com/janet-lang/janet) or
[SourceHut](https://git.sr.ht/~bakpakin/janet). While the GitHub repo is the official repo,
the SourceHut mirror is actively maintained.
## Building
### macos and Unix-like
```
cd somewhere/my/projects/janet
make
make test
make repl
```
### FreeBSD
FreeBSD build instructions are the same as the unix-like build instuctions,
but you need `gmake` and `gcc` to compile.
```
cd somewhere/my/projects/janet
gmake CC=gcc
gmake test CC=gcc
gmake repl
```
### Windows
1. Install [Visual Studio](https://visualstudio.microsoft.com/thank-you-downloading-visual-studio/?sku=Community&rel=15#) or [Visual Studio Build Tools](https://visualstudio.microsoft.com/thank-you-downloading-visual-studio/?sku=BuildTools&rel=15#)
2. Run a Visual Studio Command Prompt (cl.exe and link.exe need to be on the PATH) and cd to the directory with janet.
3. Run `build_win` to compile janet.
4. Run `build_win test` to make sure everything is working.
### Emscripten
To build janet for the web via [Emscripten](https://kripken.github.io/emscripten-site/), make sure you
have `emcc` installed and on your path. On a linux or macOS system, use `make emscripten` to build
`janet.js` and `janet.wasm` - both are needed to run janet in a browser or in node.
The JavaScript build is what runs the repl on the main website,
but really serves mainly as a proof of concept. Janet will run slower in a browser.
Building with emscripten on windows is currently unsupported.
### Meson
Janet also has a build file for [Meson](https://mesonbuild.com/), a cross platform build
system. This is not currently the main supported build system, but should work on any
system that supports meson. Meson also provides much better IDE integration than Make or batch files.
## Installation
See [the Introduction](https://janet-lang.org/introduction.html) for more details.
## Usage
A repl is launched when the binary is invoked with no arguments. Pass the -h flag
to display the usage information. Individual scripts can be run with `./janet myscript.janet`
If you are looking to explore, you can print a list of all available macros, functions, and constants
by entering the command `(all-bindings)` into the repl.
```
$ ./janet
Janet 0.0.0 alpha Copyright (C) 2017-2018 Calvin Rose
janet:1:> (+ 1 2 3)
6
janet:2:> (print "Hello, World!")
Hello, World!
nil
janet:3:> (os/exit)
$ ./janet -h
usage: ./janet [options] scripts...
Options are:
-h Show this help
-v Print the version string
-s Use raw stdin instead of getline like functionality
-e Execute a string of janet
-r Enter the repl after running all scripts
-p Keep on executing if there is a top level error (persistent)
-- Stop handling option
$
```
If installed, you can also run `man janet` to get usage information.
## Embedding
The C API for Janet is not yet documented but coming soon.
Janet can be embedded in a host program very easily. There is a make target
`make amalg` which creates the file `build/janet.c`, which is a single C file
that contains all the source to Janet. This file, along with
`src/include/janet.h` and `src/include/janetconf.h` can dragged into any C
project and compiled into the project. Janet should be compiled with `-std=c99`
on most compilers, and will need to be linked to the math library, `-lm`, and
the dynamic linker, `-ldl`, if one wants to be able to load dynamic modules. If
there is no need for dynamic modules, add the define
`-DJANET_NO_DYNAMIC_MODULES` to the compiler options.
## Examples
See the examples directory for some example janet code.
## Discussion
Feel free to ask questions and join discussion on the [Janet Gitter Channel](https://gitter.im/janet-language/community).
Alternatively, check out [the #janet channel on Freenode](https://webchat.freenode.net/)
## Why Janet
Janet is named after the almost omniscient and friendly artificial being in [The Good Place](https://en.wikipedia.org/wiki/The_Good_Place).
