A programmable configuration language.

Programmers commonly customize the behavior of their programs using configuration files. You might be familiar with configuration file formats such as JSON, YAML, XML, TOML , and INI files. However, these configuration file formats are not programmable, so you cannot simplify repetitive configuration blocks.

Dhall is a programmable configuration language optimized for maintainability.

You can think of Dhall as: JSON + functions + types + imports

Note that while Dhall is programmable, Dhall is not Turing-complete. Many of Dhall's features take advantage of this restriction to provide stronger safety guarantees and more powerful tooling.

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.

{- More than one user?  Use a function! -}

let makeUser = \(user : Text) ->
      let home       = "/home/${user}"
      let privateKey = "${home}/.ssh/id_ed25519"
      let publicKey  = "${privateKey}.pub"
      in  { home = home
          , privateKey = privateKey
          , publicKey = publicKey
          }
    {- Add another user to this list -}
in  [ makeUser "bill"
    , makeUser "jane"
    ]
Information updated 01/18/20
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