https://dhall-lang.org/

Dhall logo

  * Get started
  * Discussion
    Programmable configuration files
    Core language features
    Safety guarantees
    Dhall in production
    Design choices
  * Tutorial
    Getting started: Generate JSON or YAML
    Language tour
    Learn Dhall in Y minutes
    dhall-nethack
  * How-to guides
    How to integrate Dhall
    Cheatsheet
    Frequently Asked Questions (FAQ)
    How to translate recursive code to Dhall
    How to add a new built-in function
    How to type-check and normalize incomplete code How to validate a
    configuration file
  * References
    Grammar
    Semantics
    Built-in types, functions, and operators
    Prelude
  * Languages
    Bash logoBash
    Clojure logoClojure
    Go logoGo
    Haskell logoHaskell
    Nix logoNix
    Ruby logoRuby
    Rust logoRust
  * File formats
    YAML logoYAML
    JSON logoJSON
    XML logoXML
  * Packages
    Ansible logoAnsible
    Argo CD logoArgo CD
    CloudFormation logoCloudFormation
    Concourse logoConcourse
    Docker logoDocker
    GitLab logoGitLab
    kops logokops
    Kubernetes logoKubernetes
    Nomad logoNomad
    Prometheus logoPrometheus
  * GitHub logo
  * Twitter logo
  * Discourse logo
  * Slack logo
  * Zulip logo
  * 
  * Stack Overflow logo
  * Open Collective logo

The Dhall configuration language

Maintainable configuration files

Dhall is a programmable configuration language that you can think of
as: JSON + functions + types + imports

  * Hello, world!
  * Definitions
  * Functions
  * Types
  * Imports

[                    ]

  * Type
  * Normalized
  * Hash
  * JSON
  * YAML

[                    ]

Don't repeat yourself

Struggling with configuration drift? Create a single source of truth
you can reference everywhere.

---------------------------------------------------------------------


    "Configuration drift occurs when a standardized group of IT
    resources, be they virtual servers, standard router
    configurations in VNF deployments, or any other deployment group
    that is built from a standard template, diverge in configuration
    over time. ... The Infrastructure as Code methodology from DevOps
    is designed to combat Configuration Drift and other
    infrastructure management problems."

    Kemp Technologies on Configuration Drift
    -----------------------------------------------------------------

Create a single authoritative configuration file:

[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]
[                    ]

... that you can read directly into several languages or convert to
other file formats (including YAML or JSON).

[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ]                       
[                    ] Supported integrations

Fearlessly refactor

Need to clean up a big mess? Move fast without breaking things by
leaning on Dhall's tooling.

---------------------------------------------------------------------

Refactoring something mission-critical? Use Dhall's support for
semantic hashes to guarantee that many types of refactors are
behavior-preserving

A screencast: the semantic hash of a Dhall expression is invariant
under a series of refactorings.
[hash]
---------------------------------------------------------------------

What if you intend to make a change? Use a semantic diff to verify
that you changed what you expected to:

[                    ]
---------------------------------------------------------------------

Did you inherit a messy configuration? Use the type system and
integrated editor support to navigate more effectively.

Syntax highlighting, clickable imports, tooltips displaying
expression types and autocompletion of Dhall code in the VSCode
editor.

VSCode plugin

Safety first

Sick of Turing-complete configuration languages? Dhall is a total
programming language that forbids arbitrary side effects.

---------------------------------------------------------------------

We take language security seriously so that your Dhall programs never
fail, hang, crash, leak secrets, or compromise your system.

The language aims to support safely importing and evaluating
untrusted Dhall code, even code authored by malicious users. We treat
the inability to do so as a specification bug.

Safety guarantees

Use programming language features

Hold your configuration files to the same standard of quality as the
rest of your code.
---------------------------------------------------------------------
[                    ]


    "Configuration bugs, not code bugs, are the most common cause
    I've seen of really bad outages. ... As with error handling, I'm
    often told that it's obvious that config changes are scary, but
    it's not so obvious that most companies test and stage config
    changes like they do code changes."

    Dan Luu in Reading postmortems

    Configs are code are configs are code https://t.co/fVBs7T7P3j

    -- Charity Majors (@mipsytipsy) October 17, 2019

    Configuration testing is quite underrated in an industry where
    the majority of work is becoming configuration.

    -- JBD (@rakyll) September 26, 2019

Get started
---------------------------------------------------------------------

This work is licensed under a Creative Commons Attribution 4.0
International License.