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.

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Implemented in mostly standard C99, janet runs on Windows, Linux and macOS. The few features that are not standard C (dynamic library loading, compiler specific optimizations), are fairly straight forward. Janet can be easily ported to new platforms.

For syntax highlighting, there is some preliminary vim syntax highlighting in janet.vim. Generic lisp syntax highlighting should, however, provide good results. One can also generate a janet.tmLanguage file for other programs with make grammar.

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 for more details.
• For an overview of functions in the core library, see the function index.
• For the full API for all functions in the core library, see the core API doc

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.

Installation

See the Introduction 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. Alternatively, check out the #janet channel on Freenode

Why Janet

Janet is named after the almost omniscient and friendly artificial being in The Good Place.