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78 lines
4.3 KiB
Markdown
78 lines
4.3 KiB
Markdown
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# Architecture
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This chapter describes how Nix works.
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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.
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## Overview
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Nix consists of [hierarchical layers].
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[hierarchical layers]: https://en.m.wikipedia.org/wiki/Multitier_architecture#Layers
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```
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+---------------------------------------------------------------+
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| Nix |
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| [ commmand line interface ]------, |
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| evaluates | |
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| | manages |
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| V | |
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| [ configuration language ] | |
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| +----------------------------|-------------------V----------+ |
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| | store evaluates to | |
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| | referenced by V builds | |
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| | [ build input ] ---> [ build plan ] ---> [ build result ] | |
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| | | |
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| +-----------------------------------------------------------+ |
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+---------------------------------------------------------------+
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```
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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.
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Below that is the [Nix language](../language/index.md), a [purely functional] configuration language.
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It is used to compose expressions which ultimately evaluate to self-contained *build plans*, used to derive *build results* from referenced *build inputs*.
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[purely functional]: https://en.m.wikipedia.org/wiki/Purely_functional_programming
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Command line interface and Nix language are what users interact with most.
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> **Note**
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> The Nix language itself does not have a notion of *packages* or *configurations*.
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> As far as we are concerned here, the inputs and results of a build plan are just data.
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Underlying these is the [Nix store](../glossary.md#gloss-store), a mechanism to keep track of build plans, data, and references between them.
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It can also execute build plans to produce new data.
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A build plan is a series of *build tasks*.
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Each build task has a special build input, which is used as *build instructions*.
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The result of a build task can be input to another build task.
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> **Important**
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> A build task in Nix is called [derivation](../glossary#gloss-derivation).
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```
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+----------------------------------------------------------------------------------+
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| store .............................................. |
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| : build plan : |
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| : : |
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| [ build input ]---instructions-, : |
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| : | : |
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| : v : |
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| [ build input ]--------->[ build task ]-instructions-, : |
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| : | : |
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| : v : |
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| [ build input ]---instructions-, [ build task ]--->[ build result ] |
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| : | ^ : |
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| : v | : |
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| [ build input ]--------->[ build task ]--------------' : |
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| : ^ : |
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| : | : |
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| [ build input ]----------------' : |
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| : : |
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| :............................................: |
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+----------------------------------------------------------------------------------+
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```
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