Dhall

Dhall is a statically typed, pure functional configuration language designed to be a safe, maintainable alternative to conventional formats such as JSON and YAML. It emphasizes reproducibility and safety by being total and strongly normalizing, so configuration evaluation is deterministic and terminates.

The language provides a compact core with constructs for records, unions, lists, options, and higher‑order functions. Configurations are assembled from reusable components via an import system that can pull in local files or remote resources, with implementation‑dependent support for caching and integrity verification.

Dhall's type system includes primitive types such as Bool and Text, along with composite types like lists, records, and optional values. Type inference is supported, but explicit annotations are common for clarity. The language avoids side effects and I/O during evaluation; imports are resolved first, after which a normal form is produced.

Dhall is designed to be non‑Turing complete and strongly normalizing, guaranteeing termination and referential transparency. It aims to prevent unexpected runtime errors in deployment pipelines by catching errors at configuration time rather than at runtime.

Tooling for Dhall includes an official reference implementation and several language bindings. The command line tool dhall can type-check, normalize, and format expressions, and there are converters that translate Dhall to JSON or YAML for downstream systems.

Dhall has been adopted in infrastructure as code and configuration management to enable modular, reusable, and versioned configurations across environments. It is maintained as an open‑source project with multiple implementations and an active ecosystem of libraries and tooling.