9c8b904b56
This is only the introductory text, without any of the components specified so far. Change-Id: I6cd8eff6ec2daf14cc2420ee0a8e8983bfaa57d9 Reviewed-on: https://cl.tvl.fyi/c/depot/+/3052 Tested-by: BuildkiteCI Reviewed-by: grfn <grfn@gws.fyi> Reviewed-by: flokli <flokli@flokli.de> Reviewed-by: sterni <sternenseemann@systemli.org>
78 lines
2.9 KiB
Markdown
78 lines
2.9 KiB
Markdown
---
|
|
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.
|