113 lines
4 KiB
XML
113 lines
4 KiB
XML
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="sec-language-operators">
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<title>Operators</title>
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<para><xref linkend='table-operators' /> lists the operators in the
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Nix expression language, in order of precedence (from strongest to
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weakest binding).</para>
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<table xml:id='table-operators'>
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<title>Operators</title>
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<tgroup cols='3'>
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<thead>
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<row>
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<entry>Syntax</entry>
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<entry>Associativity</entry>
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<entry>Description</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><replaceable>e</replaceable> <literal>.</literal>
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<replaceable>attrpath</replaceable>
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[ <literal>or</literal> <replaceable>def</replaceable> ]
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</entry>
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<entry>none</entry>
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<entry>Select attribute denoted by the attribute path
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<replaceable>attrpath</replaceable> from set
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<replaceable>e</replaceable>. (An attribute path is a
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dot-separated list of attribute names.) If the attribute
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doesn’t exist, return <replaceable>def</replaceable> if
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provided, otherwise abort evaluation.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <replaceable>e2</replaceable></entry>
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<entry>left</entry>
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<entry>Call function <replaceable>e1</replaceable> with
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argument <replaceable>e2</replaceable>.</entry>
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</row>
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<row>
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<entry><replaceable>e</replaceable> <literal>?</literal>
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<replaceable>attrpath</replaceable></entry>
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<entry>none</entry>
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<entry>Test whether set <replaceable>e</replaceable> contains
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the attribute denoted by <replaceable>attrpath</replaceable>;
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return <literal>true</literal> or
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<literal>false</literal>.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>++</literal> <replaceable>e2</replaceable></entry>
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<entry>right</entry>
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<entry>List concatenation.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>+</literal> <replaceable>e2</replaceable></entry>
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<entry>left</entry>
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<entry>String or path concatenation.</entry>
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</row>
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<row>
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<entry><literal>!</literal> <replaceable>e</replaceable></entry>
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<entry>left</entry>
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<entry>Boolean negation.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>//</literal>
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<replaceable>e2</replaceable></entry>
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<entry>right</entry>
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<entry>Return a set consisting of the attributes in
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<replaceable>e1</replaceable> and
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<replaceable>e2</replaceable> (with the latter taking
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precedence over the former in case of equally named
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attributes).</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>==</literal>
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<replaceable>e2</replaceable></entry>
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<entry>none</entry>
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<entry>Equality.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>!=</literal>
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<replaceable>e2</replaceable></entry>
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<entry>none</entry>
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<entry>Inequality.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>&&</literal>
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<replaceable>e2</replaceable></entry>
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<entry>left</entry>
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<entry>Logical AND.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>||</literal>
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<replaceable>e2</replaceable></entry>
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<entry>left</entry>
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<entry>Logical OR.</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> <literal>-></literal>
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<replaceable>e2</replaceable></entry>
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<entry>none</entry>
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<entry>Logical implication (equivalent to
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<literal>!<replaceable>e1</replaceable> ||
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<replaceable>e2</replaceable></literal>).</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</section>
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