Program in YAML

YAMLScript is a functional programming language with a stylized YAML syntax.

YAMLScript can be used for:

• Writing programs and apps
• Writing reusable libraries
• Functional operations in YAML data files

YAMLScript programs can either be "run" or "loaded". When a YAMLScript program is run, it is executed as a normal program. When a YAMLScript program is loaded, it evaluates to a JSON-model data structure.

Most existing YAML files in the wild are already valid YAMLScript programs. If you have a valid YAML (1.2 Core Schema) file that doesn't use custom tags, and loads to a value expressable in JSON, then it is a valid YAMLScript program. YAMLScript's load operation will evaluate that file exactly the same in any programming language / environment.

These existing YAML files obviously can't use YAMLScript's functional programming features since that would be ambiguous. For example, what is the JSON value when "loading" this YAMLScript program?

foo: inc(41)

Is it {"foo": "inc(41)"} or {"foo": 42}?

YAMLScript programs must start with a special YAML tag !yamlscript/v0 to indicate that they have functional capabilities.

!yamlscript/v0:
foo: ! inc(41)

Note: The /v0 in the tag indicates the YAMLScript API version. This is so that future versions of YAMLScript can run programs written to an older API version, and also so that older versions of YAMLScript don't try to run programs written to a newer API version.

There are two primary ways to use YAMLScript:

• Using the ys command line runner / loader / compiler
• Using it a library in your own programming language

The ys command line tool is the easiest way to get started with YAMLScript. It has these main modes of operation:

• ys --run <file> - Run a YAMLScript program
• ys --load <file> - Load a YAMLScript program
• ys --compile <file> - Compile a YAMLScript program to Clojure
• ys --eval '<expr>' - Evaluate a YAMLScript expression string
• ys --repl - Start an interactive YAMLScript REPL session
• ys --help - Show the ys command help

You can also use YAMLScript as a library in your own programming language. For example, in Python you can use the yamlscript module like this:

import yamlscript
ys = yamlscript.new(v=0)
text = open("foo.yaml").read()
data = ys.load(text)

YAMLScript is supported on these operating systems:

• Linux
• macOS
• Windows (work in progress)

YAMLScript is supported on these architectures:

• x86-64
• ARM64

For now other systems cannot be supported because ys and libyamlscript are compiled by GraalVM's native-image tool, which only supports the above systems.

Even though YAMLScript often has the look of an imperative programming language, it actually is just a (YAML based) syntax that compiles to Clojure code. The resulting Clojure code is then run by a native-machine-code Clojure runtime called Small Clojure Interpreter (SCI).

Clojure is a functional programming language with its own Lisp syntax. Therefore it is fair to say that YAMLScript is a (functional) Lisp, even though it commonly doesn't look like one syntactically.

Typically Clojure produces Java bytecode that is run on the JVM, but for YAMLScript there is no Java or JVM involved. In testing so far, YAMLScript programs tend to run as faster or faster than equivalent Perl or Python programs.

For getting started with YAMLScript, you don't need to know anything about Lisp or Clojure. You can use it with as much or as little Lisp-ness as you want; the syntax is quite flexible (and even programmable!). As your YAMLScript programming requirements grow, you can rest assured that you have the full power of Clojure at your disposal.

At the moment, the best way to install YAMLScript is to build it from source.

This is very easy to do because YAMLScript has very few dependencies:

• bash (your interactive shell can be any shell)
• curl
• git
• make
• zlib-dev (need this installed on Linux)

To install the ys command line tool, and libyamlscript shared library, run these commands:

git clone https://github.com/yaml/yamlscript
cd yamlscript
make build
sudo make install

The make install command will install ys and libyamlscript to /usr/local/bin and /usr/local/lib respectively, by default. This means that you will need to run make install with sudo or as root. To install to a different location, run make install PREFIX=/some/path.

Notes:

• make install triggers a make build if needed, but...
• You need to run make build not as root
• The build can take several minutes (native-image is slow)
• If you install to a custom location, you will need to add that location to your PATH and LD_LIBRARY_PATH environment variables

Note: This is still a work in progress.

For Python you can simply install the yamlscript module from PyPI, like any other Python module:

pip install yamlscript

But you will also need to install the libyamlscript shared library as detailed above.

The shared library is not installed along with the Python module for many reasons, but the good news is that you can install it once and use it with any YAMLScript binding for any programming language.

The YAMLScript source code repository is a mono-repo containing:

• The YAMLScript compiler code
• The YAMLScript shared library code
• A YAMLScript binding module for each programming language
• The YAMLScript test suite
• The YAMLScript documentation
• The yamlscript.org website (with docs, blog, wiki, etc)

The YAMLScript repository uses a Makefile system to build, test and install its various offerings. There is a top level Makefile and each repo subdirectory has its own Makefile. When run at the top level, many make targets like test, build, install, clean, distclean, etc will invoke that target in each relevant subdirectory.

Given that this repository has so few dependencies, you should be able to clone it and run make targets (try make test) without any problems.

To ensure that YAMLScript libraries work the same across all languages, this project aims to have a binding implementaion for each programming language.

If you would like to contribute a new YAMLScript binding for a programming language, you are encouraged to submit a pull request to this repository.

Note: The documentation linked to below is out of date, but should give you a decent idea of what YAMLScript is about. It will be rewritten soon.

• YAMLScript Documentation
• Example YAMLScript Programs
• YAMLScript Presentation Video

• Ingy döt Net ingy@ingy.net

Copyright 2022-2023 by Ingy döt Net

This is free software, licensed under:

The MIT (X11) License