YS / YAMLScript

Add Logic to Your YAML Files

Synopsis

Load file.yaml with YS:

!YS-v0:

# Get data from external sources:
names-url =:
  "https://raw.githubusercontent.com/dominictarr/\
   random-name/master/first-names.json"

name-list =: &first-names json/load(curl(names-url))

# Data object with literal keys and generated values:
name:: rand-nth(*first-names)
aka:: name-list.rand-nth()
age:: &num 2 * 3 * 7
color:: &hue qw(red green blue yellow)
          .shuffle()
          .first()
title:: "$(*num) shades of $(*hue)."

and get:

{
  "name": "Dolores",
  "aka": "Anita",
  "age": 42,
  "color": "green",
  "title": "42 shades of green."
}

Description

YS is a functional programming language with a clean YAML syntax.

YS can be used for enhancing ordinary YAML files with functional operations, such as:

• Import (parts of) other YAML files to any node
• String interpolation including function calls
• Data transforms including ones defined by you

This YS library should be a drop-in replacement for your current YAML loader!

Most existing YAML files are already valid YS files. This means that YS works as a normal YAML loader, but can also evaluate functional expressions if asked to.

Under the hood, YS code compiles to the Clojure programming language. This makes YS a complete functional programming language right out of the box.

Even though YS compiles to Clojure, and Clojure compiles to Java, there is no dependency on Java or the JVM. YS is compiled to a native shared library (libyamlscript.so) that can be used by any programming language that can load shared libraries.

To see the Clojure code that YS compiles to, you can use the YS CLI binary ys to run:

$ ys --compile file.ys
(let
 [names-url "https://raw.githubusercontent.com/dominictarr/random-name/master/first-names.json"
  name-list (_& 'first-names (json/load (curl names-url)))]
 (%
  "name" (rand-nth (_** 'first-names))
  "aka" (rand-nth name-list)
  "age" (_& 'num (mul+ 2 3 7))
  "color" (_& 'hue (first (shuffle (qw red green blue yellow))))
  "title" (str (_** 'num) " shades of " (_** 'hue) ".")))

Crystal Usage

Here's a simple example of using the YAMLScript Crystal binding:

require "yamlscript"

# YAMLScript code
ys_code = <<-YS
!YS-v0
inc: 41
YS

# Load and evaluate the YAMLScript
result = YAMLScript.load(ys_code)
puts "Result: #{result}"  # Output: Result: 42

# Regular YAML also works
yaml_code = "foo: bar"
result = YAMLScript.load(yaml_code)
puts "YAML result: #{result["foo"]}"  # Output: YAML result: bar

Development

To build and run tests:

# Clone the repository
git clone https://github.com/yaml/yamlscript.git
cd yamlscript/crystal

# Build the binding and copy required libraries
make build

# Run the tests
make test

# Run the example
make run-example

See Also

• YS Web Site
• YS Blog
• YS Source Code
• YS Samples
• YS Programs
• YAML
• Clojure

Authors

• Josephine Pfeiffer
• Ingy döt Net

License & Copyright

Copyright 2022-2025 Ingy döt Net ingy@ingy.net

This project is licensed under the terms of the MIT license. See LICENSE for more details.