diff options
Diffstat (limited to 'doc/manual/writing-nix-expressions.xml')
| -rw-r--r-- | doc/manual/writing-nix-expressions.xml | 63 |
1 files changed, 59 insertions, 4 deletions
diff --git a/doc/manual/writing-nix-expressions.xml b/doc/manual/writing-nix-expressions.xml index 77431f9617a9..41b1723105f1 100644 --- a/doc/manual/writing-nix-expressions.xml +++ b/doc/manual/writing-nix-expressions.xml @@ -595,9 +595,54 @@ language.</para> <itemizedlist> - <listitem><para><emphasis>Strings</emphasis>, - enclosed between double quotes, e.g., <literal>"foo bar"</literal>. - TODO: antiquotations, escaping.</para></listitem> + <listitem> + + <para><emphasis>Strings</emphasis> are enclosed between double + quotes, e.g., <literal>"foo bar"</literal>. Strings can span + multiple lines. The special characters <literal>"</literal> and + <literal>\</literal> and the character sequence + <literal>${</literal> must be escaped by prefixing them with a + backslash (<literal>\</literal>). Newlines, carriage returns and + tabs can be written as <literal>\n</literal>, + <literal>\r</literal> and <literal>\t</literal>, + respectively.</para> + + <para>You can include the result of an expression into a string by + enclosing it in + <literal>${<replaceable>...</replaceable>}</literal>, a feature + known as <emphasis>antiquotation</emphasis>. The enclosed + expression must evaluate to something that can be coerced into a + string (meaning that it must be a string, a path, or a + derivation). For instance, rather than writing + +<programlisting> +"--with-freetype2-library=" + freetype + "/lib"</programlisting> + + (where <varname>freetype</varname> is a derivation), you can + instead write the more natural + +<programlisting> +"--with-freetype2-library=${freetype}/lib"</programlisting> + + The latter is automatically translated to the former. A more + complicated example (from the Nix expression for <link + xlink:href='http://www.trolltech.com/products/qt'>Qt</link>): + +<programlisting> +configureFlags = " + -system-zlib -system-libpng -system-libjpeg + ${if openglSupport then "-dlopen-opengl + -L${mesa}/lib -I${mesa}/include + -L${libXmu}/lib -I${libXmu}/include" else ""} + ${if threadSupport then "-thread" else "-no-thread"}</programlisting> + + Note that Nix expressions and strings can be arbitrarily nested; + in this case the outer string contains various antiquotations that + themselves contain strings (e.g., <literal>"-thread"</literal>), + some of which in turn contain expressions (e.g., + <literal>${mesa}</literal>).</para> + + </listitem> <listitem><para><emphasis>Integers</emphasis>, e.g., <literal>123</literal>.</para></listitem> @@ -1272,7 +1317,17 @@ command-line argument. See <xref linkend='sec-standard-environment' <section><title>Built-in functions</title> -<para>TODO</para> +<para>This section lists the functions and constants built into the +Nix expression evaluator. (The built-in function +<function>derivation</function> is discussed above.) Some built-ins, +such as <function>derivation</function>, are always in scope of every +Nix expression; you can just access them right away. But to prevent +polluting the namespace too much, most built-ins are not in scope. +Instead, you can access them through the <varname>builtins</varname> +built-in value, which is an attribute set that contains all built-in +functions and values. For instance, <function>derivation</function> +is also available as <function>builtins.derivation</function>.</para> + <variablelist> |