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diff --git a/doc/manual/src/design/overview.md b/doc/manual/src/design/overview.md index 9329f2ad7..6a5555dff 100644 --- a/doc/manual/src/design/overview.md +++ b/doc/manual/src/design/overview.md @@ -2,14 +2,22 @@ Nix consists of layers that operate fairly independently. -At the top is the *command line interface*. +At the top is the *command line interface*, translating from invocations of Nix executables to interactions with the underlying layers. -Below that is the Nix *expression language*, in which packages and configurations are written. +Below that is the *Nix language*, a [purely functional programming](https://en.m.wikipedia.org/wiki/Purely_functional_programming) language. +It is used to compose expressions which ultimately evaluate to *derivations* — self-contained *build plans* to derive new data from referenced input data. -The command line and expression 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 result of a derivation is just data. +In practice this amounts to a set of files in a file system. +::: -Below that is the *store layer*, Nix' machinery to represent tracked files, dependencies, and fully elaborated build plans. -It is also used for executing those build plans. -The store layer may not be as visible, but this is the heart of Nix. +The command line and Nix language are what users interact with most. + +Underlying everything is the *Nix store*, a mechanism to keep track of derivations, data, and references between them. +It can also *realise derivations*, that is, *execute build instructions* to produce new data. +It uses the file system as a persistence layer, and a database to keep track of references. + +This chapter describes Nix starting at the bottom with the store layer, working its way up to the user-facing components described in the rest of the manual. -This chapter describes Nix starting with that bottom store layer, then working its way up until it reaches the more user-facing interfaces described in the rest of the manual." |