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This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
28 lines
1.7 KiB
Markdown
28 lines
1.7 KiB
Markdown
# Scoping rules
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A *scope* in the Nix language is a dictionary keyed by [name](./identifiers.md#names), mapping each name to an expression and a *definition type*.
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The definition type is either *explicit* or *implicit*.
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Each entry in this dictionary is a *definition*.
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Explicit definitions are created by the following expressions:
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- [let-expressions](syntax.md#let-expressions)
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- [recursive attribute set literals](syntax.md#recursive-sets) (`rec`)
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- [function literals](syntax.md#functions)
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Implicit definitions are only created by [with-expressions](./syntax.md#with-expressions).
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Every expression is *enclosed* by a scope.
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The outermost expression is enclosed by the [built-in, global scope](./builtins.md), which contains only explicit definitions.
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The expressions listed above *extend* their enclosing scope by adding new definitions, or replacing existing ones with the same name.
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An explicit definition can replace a definition of any type; an implicit definition can only replace another implicit definition.
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Each of the above expressions defines which of its subexpressions are enclosed by the extended scope.
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In all other cases, the same scope that encloses an expression is the enclosing scope for its subexpressions.
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The Nix language is [statically scoped](https://en.wikipedia.org/wiki/Scope_(computer_science)#Lexical_scope);
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the value of a variable is determined only by the variable's enclosing scope, and not by the dynamic context in which the variable is evaluated.
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> **Note**
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>
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> Expressions entered into the [Nix REPL](@docroot@/command-ref/new-cli/nix3-repl.md) are enclosed by a scope that can be extended by command line arguments or previous REPL commands.
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> These ways of extending scope are not, strictly speaking, part of the Nix language.
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