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* Operators, comments.

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Eelco Dolstra 2004-11-07 18:58:49 +00:00
parent 55b35d6d77
commit 1bac7a10e6
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125
doc/manual/writing-nix-expressions.xml
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@ -933,14 +933,126 @@ used in the Nix expression for Subversion.</para>
<simplesect><title>With expressions</title>
<para>TODO</para>
<para>A <emphasis>with</emphasis> expression,
<programlisting>
with <replaceable>e1</replaceable>; <replaceable>e2</replaceable></programlisting>
introduces the attribute set <replaceable>e1</replaceable> into the
lexical scope of the expression <replaceable>e2</replaceable>. For
instance,
<programlisting>
let {
as = {x = "foo"; y = "bar";};
body = with as; x + y;
}</programlisting>
evaluates to <literal>"foobar"</literal> since the
<literal>with</literal> adds the <varname>x</varname> and
<varname>y</varname> attributes of <varname>as</varname> to the
lexical scope in the expression <literal>x + y</literal>. The most
common use of <literal>with</literal> is in conjunction with the
<function>import</function> function. E.g.,
<programlisting>
with (import ./definitions.nix); ...</programlisting>
makes all attributes defined in the file
<filename>definitions.nix</filename> available as if they were defined
locally in a <literal>rec</literal>-expression.</para>
</simplesect>
<simplesect><title>Operators</title>
<para>TODO</para>
<para><xref linkend='table-operators' /> lists the operators in the
Nix expression language, in order of precedence (from strongest to
weakest binding).</para>
<table 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>e1</replaceable> ~ <replaceable>e2</replaceable></entry>
<entry>none</entry>
<entry>Construct a reference to a subpath of a derivation.
E.g., <literal>hello ~ "/bin/sh"</literal> refers to the
<filename>/bin/sh</filename> path within the Hello derivation.
Useful in specifying derivation attributes.</entry>
</row>
<row>
<entry><replaceable>e</replaceable> ?
<replaceable>id</replaceable></entry>
<entry>none</entry>
<entry>Test whether attribute set <replaceable>e</replaceable>
contains an attribute named
<replaceable>id</replaceable>.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> + <replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>String or path concatenation.</entry>
</row>
<row>
<entry>! <replaceable>e</replaceable></entry>
<entry>left</entry>
<entry>Boolean negation.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> //
<replaceable>e2</replaceable></entry>
<entry>right</entry>
<entry>Return an attribute 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> ==
<replaceable>e2</replaceable></entry>
<entry>none</entry>
<entry>Equality.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> !=
<replaceable>e2</replaceable></entry>
<entry>none</entry>
<entry>Inequality.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> &amp;&amp;
<replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Logical AND.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> ||
<replaceable>e2</replaceable></entry>
<entry>left</entry>
<entry>Logical OR.</entry>
</row>
<row>
<entry><replaceable>e1</replaceable> ->
<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>
</simplesect>
@ -959,6 +1071,15 @@ used in the Nix expression for Subversion.</para>
</simplesect>
<simplesect><title>Comments</title>
<para>Comments can be single-line, started with a <literal>#</literal>
character, or inline/multi-line, enclosed within <literal>/*
... */</literal>.</para>
</simplesect>
</sect1>