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diff --git a/tvix/docs/language-spec.md b/tvix/docs/language-spec.md new file mode 100644 index 000000000000..a71437493307 --- /dev/null +++ b/tvix/docs/language-spec.md @@ -0,0 +1,78 @@ +--- +title: "Specification of the Nix language" +numbersections: true +author: +- tazjin +email: +- tazjin@tvl.su +lang: en-GB +--- + +The Nix Language +================ + +WARNING: This document is a work in progress. Please keep an eye on +[`topic:nix-spec`](https://cl.tvl.fyi/q/topic:nix-spec) for ongoing +CLs. + +Nix is a general-purpose, functional programming language which this +document aims to describe. + +## Background + +Nix was designed and implemented as part of the [Nix package +manager](https://nixos.org/nix). It is primarily used for generating +so-called [*derivations*](#derivations), which are data structures +describing how to build a package. + +The language has been described in the +[thesis](https://edolstra.github.io/pubs/phd-thesis.pdf) introducing +the package manager, but only on a high-level. At the time of writing, +Nix is informally specified (via its only complete implementation in +the package manager) and there is no complete overview over its - +sometimes surprising - semantics. + +The primary project written in Nix is +[nixpkgs](https://github.com/NixOS/nixpkgs/). Uncertainties in the +process of writing this specification are resolved by investigating +patterns in nixpkgs, which we consider canonical. The code in nixpkgs +uses a reasonable subset of the features exposed by the current +implementation, some of which are *accidental*, and is thus more +useful for specifying how the language should work. + +## Introduction to Nix + +Nix is a general-purpose, partially lazy, functional programming +language which provides higher-order functions, type reflection, +primitive data types such as integers, strings and floats, and +compound data structures such as lists and attribute sets. + +Nix has syntactic sugar for common operations, such as those for +attribute sets, and also provides a wide range of built-in functions +which have organically accumulated over time. + +Nix has a variety of legacy features that are not in practical use, +but are documented in sections of this specification for the sake of +completeness. + +This document describes the syntax and abstract semantics of the Nix +language, but leaves out implementation details about how Nix can be +interpreted/compiled/analysed etc. + +### Program structure + +This section describes the semantic structure of Nix, and how it +relates to the rest of the specification. + +Each Nix program is a single [*expression*](#expressions) denoting a +[*value*](#values) (commonly a [*function*](#functions)). Each value +has a [*type*](#types), however this type is not statically known. + +Nix code is modularised through the use of the +[*import*](#builtins-import) built-in function. No separate module +system exists. + +In addition to chapters describing the building blocks mentioned +above, this specificiation also describes the [*syntax*](#syntax), the +available [built-in functions](#builtins), [*error handling*](#errors) +and known [*deficiencies*](#deficiencies) in the language. |