* Operators, comments.
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Eelco Dolstra
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1 changed files with 123 additions and 2 deletions
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@ -933,14 +933,126 @@ used in the Nix expression for Subversion.</para>
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<simplesect><title>With expressions</title>
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<para>TODO</para>
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<para>A <emphasis>with</emphasis> expression,
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<programlisting>
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with <replaceable>e1</replaceable>; <replaceable>e2</replaceable></programlisting>
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introduces the attribute set <replaceable>e1</replaceable> into the
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lexical scope of the expression <replaceable>e2</replaceable>. For
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instance,
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<programlisting>
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let {
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as = {x = "foo"; y = "bar";};
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body = with as; x + y;
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}</programlisting>
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evaluates to <literal>"foobar"</literal> since the
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<literal>with</literal> adds the <varname>x</varname> and
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<varname>y</varname> attributes of <varname>as</varname> to the
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lexical scope in the expression <literal>x + y</literal>. The most
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common use of <literal>with</literal> is in conjunction with the
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<function>import</function> function. E.g.,
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<programlisting>
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with (import ./definitions.nix); ...</programlisting>
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makes all attributes defined in the file
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<filename>definitions.nix</filename> available as if they were defined
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locally in a <literal>rec</literal>-expression.</para>
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</simplesect>
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<simplesect><title>Operators</title>
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<para>TODO</para>
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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 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>e1</replaceable> ~ <replaceable>e2</replaceable></entry>
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<entry>none</entry>
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<entry>Construct a reference to a subpath of a derivation.
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E.g., <literal>hello ~ "/bin/sh"</literal> refers to the
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<filename>/bin/sh</filename> path within the Hello derivation.
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Useful in specifying derivation attributes.</entry>
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</row>
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<row>
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<entry><replaceable>e</replaceable> ?
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<replaceable>id</replaceable></entry>
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<entry>none</entry>
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<entry>Test whether attribute set <replaceable>e</replaceable>
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contains an attribute named
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<replaceable>id</replaceable>.</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>String or path concatenation.</entry>
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</row>
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<row>
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<entry>! <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> //
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<replaceable>e2</replaceable></entry>
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<entry>right</entry>
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<entry>Return an attribute 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 attributes).</entry>
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</row>
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<row>
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<entry><replaceable>e1</replaceable> ==
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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> !=
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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> &&
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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> ||
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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> ->
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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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</simplesect>
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@ -959,6 +1071,15 @@ used in the Nix expression for Subversion.</para>
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</simplesect>
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<simplesect><title>Comments</title>
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<para>Comments can be single-line, started with a <literal>#</literal>
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character, or inline/multi-line, enclosed within <literal>/*
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... */</literal>.</para>
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</simplesect>
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</sect1>
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