0
0
Fork 0
forked from lix-project/lix
lix/doc/manual/expressions/language-operators.xml
2017-10-26 18:53:35 +00:00

135 lines
5.1 KiB
XML
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-language-operators">
<title>Operators</title>
<para><xref linkend='table-operators' /> lists the operators in the
Nix expression language, in order of precedence (from strongest to
weakest binding).</para>
<table xml:id='table-operators'>
<title>Operators</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Syntax</entry>
<entry>Associativity</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><replaceable>e</replaceable> <literal>.</literal>
<replaceable>attrpath</replaceable>
[ <literal>or</literal> <replaceable>def</replaceable> ]
</entry>
<entry>none</entry>
<entry>Select attribute denoted by the attribute path
<replaceable>attrpath</replaceable> from set
<replaceable>e</replaceable>. (An attribute path is a
dot-separated list of attribute names.) If the attribute
doesnt exist, return <replaceable>def</replaceable> if
provided, otherwise abort evaluation.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> <replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Call function <replaceable>e1</replaceable> with
argument <replaceable>e2</replaceable>.</entry>
</row>
<row>
<entry><literal>-</literal> <replaceable>e</replaceable></entry>
<entry>none</entry>
<entry>Arithmetic negation.</entry>
</row>
<row>
<entry><replaceable>e</replaceable> <literal>?</literal>
<replaceable>attrpath</replaceable></entry>
<entry>none</entry>
<entry>Test whether set <replaceable>e</replaceable> contains
the attribute denoted by <replaceable>attrpath</replaceable>;
return <literal>true</literal> or
<literal>false</literal>.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> <literal>++</literal> <replaceable>e2</replaceable></entry>
<entry>right</entry>
<entry>List concatenation.</entry>
</row>
<row>
<entry>
<replaceable>e1</replaceable> <literal>*</literal> <replaceable>e2</replaceable>,
<replaceable>e1</replaceable> <literal>/</literal> <replaceable>e2</replaceable>
</entry>
<entry>left</entry>
<entry>Arithmetic multiplication and division.</entry>
</row>
<row>
<entry>
<replaceable>e1</replaceable> <literal>+</literal> <replaceable>e2</replaceable>,
<replaceable>e1</replaceable> <literal>-</literal> <replaceable>e2</replaceable>
</entry>
<entry>left</entry>
<entry>Arithmetic addition and subtraction. String or path concatenation (only by <literal>+</literal>).</entry>
</row>
<row>
<entry><literal>!</literal> <replaceable>e</replaceable></entry>
<entry>none</entry>
<entry>Boolean negation.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> <literal>//</literal>
<replaceable>e2</replaceable></entry>
<entry>right</entry>
<entry>Return a set consisting of the attributes in
<replaceable>e1</replaceable> and
<replaceable>e2</replaceable> (with the latter taking
precedence over the former in case of equally named
attributes).</entry>
</row>
<row>
<entry>
<replaceable>e1</replaceable> <literal>&lt;</literal> <replaceable>e2</replaceable>,
<replaceable>e1</replaceable> <literal>&gt;</literal> <replaceable>e2</replaceable>,
<replaceable>e1</replaceable> <literal>&lt;=</literal> <replaceable>e2</replaceable>,
<replaceable>e1</replaceable> <literal>&gt;=</literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Arithmetic comparison.</entry>
</row>
<row>
<entry>
<replaceable>e1</replaceable> <literal>==</literal> <replaceable>e2</replaceable>,
<replaceable>e1</replaceable> <literal>!=</literal> <replaceable>e2</replaceable>
</entry>
<entry>none</entry>
<entry>Equality and inequality.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> <literal>&amp;&amp;</literal>
<replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Logical AND.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> <literal>||</literal>
<replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Logical OR.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> <literal>-></literal>
<replaceable>e2</replaceable></entry>
<entry>none</entry>
<entry>Logical implication (equivalent to
<literal>!<replaceable>e1</replaceable> ||
<replaceable>e2</replaceable></literal>).</entry>
</row>
</tbody>
</tgroup>
</table>
</section>