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diff --git a/doc/manual/src/architecture/architecture.md b/doc/manual/src/architecture/architecture.md new file mode 100644 index 000000000..41deb07af --- /dev/null +++ b/doc/manual/src/architecture/architecture.md @@ -0,0 +1,79 @@ +# Architecture + +*(This chapter is unstable and a work in progress. Incoming links may rot.)* + +This chapter describes how Nix works. +It should help users understand why Nix behaves as it does, and it should help developers understand how to modify Nix and how to write similar tools. + +## Overview + +Nix consists of [hierarchical layers][layer-architecture]. + +``` ++-----------------------------------------------------------------+ +| Nix | +| [ commmand line interface ]------, | +| | | | +| evaluates | | +| | manages | +| V | | +| [ configuration language ] | | +| | | | +| +-----------------------------|-------------------V-----------+ | +| | store evaluates to | | +| | | | | +| | referenced by V builds | | +| | [ build input ] ---> [ build plan ] ---> [ build result ] | | +| | | | +| +-------------------------------------------------------------+ | ++-----------------------------------------------------------------+ +``` + +At the top is the [command line interface](../command-ref/command-ref.md), translating from invocations of Nix executables to interactions with the underlying layers. + +Below that is the [Nix expression language](../expressions/expression-language.md), a [purely functional][purely-functional-programming] configuration language. +It is used to compose expressions which ultimately evaluate to self-contained *build plans*, used to derive *build results* from referenced *build inputs*. + +The command line and Nix language are what users interact with most. + +> **Note** +> The Nix language itself does not have a notion of *packages* or *configurations*. +> As far as we are concerned here, the inputs and results of a build plan are just data. + +Underlying these is the [Nix store](./store/store.md), a mechanism to keep track of build plans, data, and references between them. +It can also execute build plans to produce new data. + +A build plan is a series of *build tasks*. +Each build task has a special build input which is used as *build instructions*. +The result of a build task can be input to another build task. + +``` ++-----------------------------------------------------------------------------------------+ +| store | +| ................................................. | +| : build plan : | +| : : | +| [ build input ]-----instructions-, : | +| : | : | +| : v : | +| [ build input ]----------->[ build task ]--instructions-, : | +| : | : | +| : | : | +| : v : | +| : [ build task ]----->[ build result ] | +| [ build input ]-----instructions-, ^ : | +| : | | : | +| : v | : | +| [ build input ]----------->[ build task ]---------------' : | +| : ^ : | +| : | : | +| [ build input ]------------------' : | +| : : | +| : : | +| :...............................................: | +| | ++-----------------------------------------------------------------------------------------+ +``` + +[layer-architecture]: https://en.m.wikipedia.org/wiki/Multitier_architecture#Layers +[purely-functional-programming]: https://en.m.wikipedia.org/wiki/Purely_functional_programming |