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Submitted URL: http://dhall-lang.org/
Effective URL: https://dhall-lang.org/
Submission: On April 30 via api from GB — Scanned from GB
Effective URL: https://dhall-lang.org/
Submission: On April 30 via api from GB — Scanned from GB
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* 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
Clojure
Go
Haskell
Nix
Ruby
Rust
* File formats
YAML
JSON
XML
* Packages
Ansible
Argo CD
CloudFormation
Concourse
Docker
GitLab
kops
Kubernetes
Nomad
Prometheus
*
*
*
*
*
*
*
*
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
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{- This is an example Dhall configuration file
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Can you spot the mistake?
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Fix the typo, then move onto the "Definitions"
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example
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-}
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{ home = "/home/bill"
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, privateKey = "/home/bill/.ssh/id_ed25519"
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, publicKey = "/home/blil/.ssh/id_ed25519.pub"
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}
* Type
* Normalized
* Hash
* JSON
* YAML
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home: /home/bill
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privateKey: /home/bill/.ssh/id_ed25519
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publicKey: /home/blil/.ssh/id_ed25519.pub
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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:
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-- ./company.dhall
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let Prelude =
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https://prelude.dhall-lang.org/v19.0.0/package.dhall sha256:eb693342eb769f782174157eba9b5924cf8ac6793897fc36a31ccbd6f56dafe2
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let companyName = "Example Dot Com"
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let User = { name : Text, account : Text, age : Natural }
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let users
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: List User
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= [ { name = "John Doe", account = "john", age = 23 }
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, { name = "Jane Smith", account = "jane", age = 29 }
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, { name = "William Allen", account = "bill", age = 41 }
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]
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let toEmail = \(user : User) -> "${user.account}@example.com"
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let Bio = { name : Text, age : Natural }
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let toBio = \(user : User) -> user.(Bio)
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let companySize = Prelude.List.length User users
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let greetingPage =
… that you can read directly into several languages or convert to other file
formats (including YAML or JSON).
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$ dhall-to-yaml <<< '(./company.dhall).bios'
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- age: 23
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name: John Doe
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- age: 29
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name: Jane Smith
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- age: 41
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name: William Allen
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$ dhall-to-bash --declare EMAILS <<< '(./company.dhall).emails'
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declare -r -a EMAILS=(john@example.com jane@example.com bill@example.com)
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$ dhall text <<< '(./company.dhall).greetingPage'
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<html>
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<title>Welcome to Example Dot Com!</title>
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<body>
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<p>Welcome to our humble company of 3 people!</p>
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</body>
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</html>
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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
--------------------------------------------------------------------------------
What if you intend to make a change? Use a semantic diff to verify that you
changed what you expected to:
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$ dhall diff \
'https://prelude.dhall-lang.org/v18.0.0/package.dhall' \
'https://prelude.dhall-lang.org/v19.0.0/package.dhall'
{ + Operator = …
, `Optional` = { + concatMap = …
, …
}
, …
}
--------------------------------------------------------------------------------
Did you inherit a messy configuration? Use the type system and integrated editor
support to navigate more effectively.
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.
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-- Import packages
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let JSON =
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https://prelude.dhall-lang.org/v19.0.0/JSON/package.dhall sha256:79dfc281a05bc7b78f927e0da0c274ee5709b1c55c9e5f59499cb28e9d6f3ec0
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-- Use precise types like enums instead of strings
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let Zone = < us-east-1 | us-west-1 >
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let InstanceType = < `m5.large` | `m5.xlarge` >
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let Instance = { type : InstanceType, zone : Zone }
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-- JSON rendering can optionally be implemented entirely within the language
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let Zone/toJSON =
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\(zone : Zone)
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-> merge
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{ us-east-1 = JSON.string "us-east-1"
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, us-west-1 = JSON.string "us-west-1"
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}
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zone
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let InstanceType/toJSON =
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\(type : InstanceType)
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-> merge
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{ `m5.large` = JSON.string "m5.large"
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, `m5.xlarge` = JSON.string "m5.xlarge"
> "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
Get started
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