332 lines
9 KiB
XML
332 lines
9 KiB
XML
<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-nix-syntax-summary">
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<title>Syntax Summary</title>
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<para>
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Below is a summary of the most important syntactic constructs in the
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Nix expression language. It’s not complete. In particular, there are
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many other built-in functions. See the
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<link xlink:href="https://nixos.org/nix/manual/#chap-writing-nix-expressions">Nix
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manual</link> for the rest.
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</para>
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<informaltable>
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<tgroup cols="2">
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<colspec align="left" />
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<colspec align="left" />
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<thead>
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<row>
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<entry>
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Example
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</entry>
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<entry>
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Description
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</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>
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<emphasis>Basic values</emphasis>
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</entry>
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<entry>
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</entry>
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</row>
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<row>
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<entry>
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<literal>"Hello world"</literal>
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</entry>
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<entry>
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A string
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</entry>
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</row>
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<row>
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<entry>
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<literal>"${pkgs.bash}/bin/sh"</literal>
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</entry>
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<entry>
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A string containing an expression (expands to
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<literal>"/nix/store/hash-bash-version/bin/sh"</literal>)
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</entry>
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</row>
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<row>
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<entry>
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<literal>true</literal>, <literal>false</literal>
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</entry>
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<entry>
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Booleans
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</entry>
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</row>
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<row>
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<entry>
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<literal>123</literal>
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</entry>
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<entry>
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An integer
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</entry>
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</row>
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<row>
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<entry>
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<literal>./foo.png</literal>
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</entry>
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<entry>
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A path (relative to the containing Nix expression)
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</entry>
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</row>
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<row>
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<entry>
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<emphasis>Compound values</emphasis>
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</entry>
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<entry>
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x = 1; y = 2; }</literal>
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</entry>
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<entry>
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A set with attributes named <literal>x</literal> and
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<literal>y</literal>
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ foo.bar = 1; }</literal>
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</entry>
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<entry>
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A nested set, equivalent to
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<literal>{ foo = { bar = 1; }; }</literal>
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</entry>
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</row>
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<row>
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<entry>
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<literal>rec { x = "foo"; y = x + "bar"; }</literal>
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</entry>
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<entry>
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A recursive set, equivalent to
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<literal>{ x = "foo"; y = "foobar"; }</literal>
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</entry>
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</row>
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<row>
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<entry>
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<literal>[ "foo" "bar" ]</literal>
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</entry>
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<entry>
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A list with two elements
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</entry>
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</row>
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<row>
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<entry>
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<emphasis>Operators</emphasis>
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</entry>
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<entry>
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</entry>
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</row>
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<row>
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<entry>
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<literal>"foo" + "bar"</literal>
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</entry>
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<entry>
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String concatenation
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</entry>
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</row>
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<row>
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<entry>
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<literal>1 + 2</literal>
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</entry>
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<entry>
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Integer addition
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</entry>
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</row>
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<row>
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<entry>
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<literal>"foo" == "f" + "oo"</literal>
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</entry>
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<entry>
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Equality test (evaluates to <literal>true</literal>)
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</entry>
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</row>
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<row>
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<entry>
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<literal>"foo" != "bar"</literal>
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</entry>
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<entry>
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Inequality test (evaluates to <literal>true</literal>)
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</entry>
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</row>
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<row>
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<entry>
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<literal>!true</literal>
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</entry>
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<entry>
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Boolean negation
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x = 1; y = 2; }.x</literal>
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</entry>
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<entry>
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Attribute selection (evaluates to <literal>1</literal>)
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x = 1; y = 2; }.z or 3</literal>
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</entry>
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<entry>
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Attribute selection with default (evaluates to
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<literal>3</literal>)
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x = 1; y = 2; } // { z = 3; }</literal>
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</entry>
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<entry>
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Merge two sets (attributes in the right-hand set taking
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precedence)
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</entry>
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</row>
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<row>
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<entry>
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<emphasis>Control structures</emphasis>
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</entry>
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<entry>
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</entry>
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</row>
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<row>
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<entry>
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<literal>if 1 + 1 == 2 then "yes!" else "no!"</literal>
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</entry>
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<entry>
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Conditional expression
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</entry>
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</row>
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<row>
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<entry>
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<literal>assert 1 + 1 == 2; "yes!"</literal>
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</entry>
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<entry>
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Assertion check (evaluates to
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<literal>"yes!"</literal>). See
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<xref linkend="sec-assertions" /> for using assertions in
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modules
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</entry>
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</row>
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<row>
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<entry>
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<literal>let x = "foo"; y = "bar"; in x + y</literal>
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</entry>
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<entry>
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Variable definition
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</entry>
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</row>
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<row>
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<entry>
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<literal>with pkgs.lib; head [ 1 2 3 ]</literal>
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</entry>
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<entry>
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Add all attributes from the given set to the scope
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(evaluates to <literal>1</literal>)
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</entry>
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</row>
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<row>
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<entry>
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<emphasis>Functions (lambdas)</emphasis>
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</entry>
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<entry>
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</entry>
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</row>
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<row>
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<entry>
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<literal>x: x + 1</literal>
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</entry>
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<entry>
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A function that expects an integer and returns it increased
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by 1
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</entry>
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</row>
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<row>
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<entry>
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<literal>(x: x + 1) 100</literal>
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</entry>
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<entry>
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A function call (evaluates to 101)
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</entry>
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</row>
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<row>
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<entry>
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<literal>let inc = x: x + 1; in inc (inc (inc 100))</literal>
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</entry>
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<entry>
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A function bound to a variable and subsequently called by
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name (evaluates to 103)
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x, y }: x + y</literal>
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</entry>
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<entry>
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A function that expects a set with required attributes
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<literal>x</literal> and <literal>y</literal> and
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concatenates them
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x, y ? "bar" }: x + y</literal>
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</entry>
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<entry>
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A function that expects a set with required attribute
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<literal>x</literal> and optional <literal>y</literal>,
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using <literal>"bar"</literal> as default value
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for <literal>y</literal>
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x, y, ... }: x + y</literal>
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</entry>
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<entry>
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A function that expects a set with required attributes
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<literal>x</literal> and <literal>y</literal> and ignores
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any other attributes
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</entry>
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</row>
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<row>
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<entry>
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<literal>{ x, y } @ args: x + y</literal>
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</entry>
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<entry>
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A function that expects a set with required attributes
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<literal>x</literal> and <literal>y</literal>, and binds the
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whole set to <literal>args</literal>
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</entry>
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</row>
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<row>
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<entry>
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<emphasis>Built-in functions</emphasis>
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</entry>
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<entry>
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</entry>
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</row>
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<row>
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<entry>
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<literal>import ./foo.nix</literal>
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</entry>
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<entry>
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Load and return Nix expression in given file
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</entry>
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</row>
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<row>
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<entry>
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<literal>map (x: x + x) [ 1 2 3 ]</literal>
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</entry>
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<entry>
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Apply a function to every element of a list (evaluates to
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<literal>[ 2 4 6 ]</literal>)
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</section>
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