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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..2d1b26558 --- /dev/null +++ b/doc/manual/src/architecture/architecture.md @@ -0,0 +1,115 @@ +# Architecture + +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]. + +[hierarchical layers]: https://en.m.wikipedia.org/wiki/Multitier_architecture#Layers + +The following [concept map] shows its main components (rectangles), the objects they operate on (rounded rectangles), and their interactions (connecting phrases): + +[concept map]: https://en.m.wikipedia.org/wiki/Concept_map + +``` + + .----------------. + | Nix expression |----------. + '----------------' | + | passed to + | | ++----------|-------------------|--------------------------------+ +| Nix | V | +| | +-------------------------+ | +| | | commmand line interface |------. | +| | +-------------------------+ | | +| | | | | +| evaluated by calls manages | +| | | | | +| | V | | +| | +--------------------+ | | +| '-------->| language evaluator | | | +| +--------------------+ | | +| | | | +| produces | | +| | V | +| +----------------------------|------------------------------+ | +| | store | | | +| | referenced by V builds | | +| | .-------------. .------------. .--------------. | | +| | | build input |----->| build plan |----->| build result | | | +| | '-------------' '------------' '--------------' | | +| +-------------------------------------------------|---------+ | ++---------------------------------------------------|-----------+ + | + represented as + | + V + .---------------. + | file | + '---------------' +``` + +At the top is the [command line interface](../command-ref/command-ref.md) that drives the underlying layers. + +The [Nix language](../language/index.md) evaluator transforms Nix expressions into self-contained *build plans*, which are used to derive *build results* from referenced *build inputs*. + +The command line interface and Nix expressions are what users deal 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 the command line interface and the Nix language evaluator is the [Nix store](../glossary.md#gloss-store), a mechanism to keep track of build plans, data, and references between them. +It can also execute build plans to produce new data, which are made available to the operating system as files. + +A build plan itself is a series of *build tasks*, together with their build inputs. + +> **Important** +> A build task in Nix is called [derivation](../glossary#gloss-derivation). + +Each build task has a special build input executed as *build instructions* in order to perform the build. +The result of a build task can be input to another build task. + +The following [data flow diagram] shows a build plan for illustration. +Build inputs used as instructions to a build task are marked accordingly: + +[data flow diagram]: https://en.m.wikipedia.org/wiki/Data-flow_diagram + +``` ++--------------------------------------------------------------------+ +| build plan | +| | +| .-------------. | +| | build input |---------. | +| '-------------' | | +| instructions | +| | | +| v | +| .-------------. .----------. | +| | build input |-->( build task )-------. | +| '-------------' '----------' | | +| instructions | +| | | +| v | +| .-------------. .----------. .--------------. | +| | build input |---------. ( build task )--->| build result | | +| '-------------' | '----------' '--------------' | +| instructions ^ | +| | | | +| v | | +| .-------------. .----------. | | +| | build input |-->( build task )-------' | +| '-------------' '----------' | +| ^ | +| | | +| | | +| .-------------. | | +| | build input |---------' | +| '-------------' | +| | ++--------------------------------------------------------------------+ +``` + |