diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/manual/writing-nix-expressions.xml | 125 |
1 files changed, 123 insertions, 2 deletions
diff --git a/doc/manual/writing-nix-expressions.xml b/doc/manual/writing-nix-expressions.xml index d81d741a8836..ac7b24c2483a 100644 --- a/doc/manual/writing-nix-expressions.xml +++ b/doc/manual/writing-nix-expressions.xml @@ -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> && + <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> |