* Document the new primops in Nix 0.11.
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Eelco Dolstra
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id='ssec-builtins'>
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<title>Built-in functions</title>
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@ -145,6 +146,58 @@ if builtins ? getEnv then __getEnv "PATH" else ""</programlisting>
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</varlistentry>
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<varlistentry><term><function>builtins.filterSource</function>
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<replaceable>e1</replaceable> <replaceable>e2</replaceable></term>
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<listitem>
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<para>This function allows you to copy sources into the Nix
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store while filtering certain files. For instance, suppose that
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you want to use the directory <filename>source-dir</filename> as
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an input to a Nix expression, e.g.
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<programlisting>
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stdenv.mkDerivation {
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...
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src = ./source-dir;
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}
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</programlisting>
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However, if <filename>source-dir</filename> is a Subversion
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working copy, then all those annoying <filename>.svn</filename>
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subdirectories will also be copied to the store. Worse, the
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contents of those directories may change a lot, causing lots of
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spurious rebuilds. With <function>filterSource</function> you
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can filter out the <filename>.svn</filename> directories:
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<programlisting>
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src = builtins.filterSource
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(path: type: type != "directory" || baseNameOf path != ".svn")
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./source-dir;
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</programlisting>
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</para>
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<para>Thus, the first argument <replaceable>e1</replaceable>
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must be a predicate function that is called for each regular
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file, directory or symlink in the source tree
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<replaceable>e2</replaceable>. If the function returns
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<literal>true</literal>, the file is copied to the Nix store,
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otherwise it is omitted. The function is called with two
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arguments. The first is the full path of the file. The second
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is a string that identifies the type of the file, which is
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either <literal>"regular"</literal>,
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<literal>"directory"</literal>, <literal>"symlink"</literal> or
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<literal>"unknown"</literal> (for other kinds of files such as
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device nodes or fifos — but note that those cannot be copied to
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the Nix store, so if the predicate returns
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<literal>true</literal> for them, the copy will fail).</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><function>builtins.getAttr</function>
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<replaceable>s</replaceable> <replaceable>attrs</replaceable></term>
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@ -254,6 +307,16 @@ x: x + 456</programlisting>
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</varlistentry>
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<varlistentry><term><function>builtins.isAttrs</function>
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<replaceable>e</replaceable></term>
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<listitem><para>Return <literal>true</literal> if
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<replaceable>e</replaceable> evaluates to an attribute set, and
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<literal>false</literal> otherwise.</para></listitem>
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</varlistentry>
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<varlistentry><term><function>builtins.isList</function>
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<replaceable>e</replaceable></term>
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@ -264,6 +327,16 @@ x: x + 456</programlisting>
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</varlistentry>
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<varlistentry><term><function>builtins.isFunction</function>
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<replaceable>e</replaceable></term>
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<listitem><para>Return <literal>true</literal> if
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<replaceable>e</replaceable> evaluates to a function, and
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<literal>false</literal> otherwise.</para></listitem>
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</varlistentry>
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<varlistentry><term><function>isNull</function>
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<replaceable>e</replaceable></term>
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@ -292,6 +365,33 @@ x: x + 456</programlisting>
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</varlistentry>
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<varlistentry><term><function>builtins.listToAttrs</function>
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<replaceable>e</replaceable></term>
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<listitem><para>Construct an attribute set from a list specifying
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the names and values of each attribute. Each element of the list
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should be an attribute set consisting of a string-valued attribute
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<varname>name</varname> specifying the name of the attribute, and
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an attribute <varname>value</varname> specifying its value.
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Example:
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<programlisting>
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builtins.listToAttrs [
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{name = "foo"; value = 123;}
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{name = "bar"; value = 456;}
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]
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</programlisting>
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evaluates to
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<programlisting>
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{ foo = 123; bar = 456; }
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</programlisting>
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</para></listitem>
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</varlistentry>
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<varlistentry><term><function>map</function>
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<replaceable>f</replaceable> <replaceable>list</replaceable></term>
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@ -357,6 +457,44 @@ removeAttrs { x = 1; y = 2; z = 3; } ["a" "x" "z"]</screen>
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</varlistentry>
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<varlistentry><term><function>builtins.stringLength</function>
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<replaceable>e</replaceable></term>
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<listitem><para>Return the length of the string
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<replaceable>e</replaceable>. If <replaceable>e</replaceable> is
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not a string, evaluation is aborted.</para></listitem>
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</varlistentry>
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<varlistentry><term><function>builtins.sub</function>
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<replaceable>e1</replaceable> <replaceable>e2</replaceable></term>
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<listitem><para>Return the difference between the integers
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<replaceable>e1</replaceable> and
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<replaceable>e2</replaceable>.</para></listitem>
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</varlistentry>
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<varlistentry><term><function>builtins.substr</function>
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<replaceable>start</replaceable> <replaceable>len</replaceable>
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<replaceable>s</replaceable></term>
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<listitem><para>Return the substring of
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<replaceable>s</replaceable> from character position
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<replaceable>start</replaceable> (zero-based) up to but not
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including <replaceable>start + len</replaceable>. If
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<replaceable>start</replaceable> is greater than the length of the
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string, an empty string is returned, and if <replaceable>start +
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len</replaceable> lies beyond the end of the string, only the
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substring up to the end of the string is returned.
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<replaceable>start</replaceable> must be
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non-negative.</para></listitem>
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</varlistentry>
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<varlistentry><term><function>builtins.tail</function>
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<replaceable>list</replaceable></term>
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@ -367,6 +505,20 @@ removeAttrs { x = 1; y = 2; z = 3; } ["a" "x" "z"]</screen>
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</varlistentry>
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<varlistentry><term><function>throw</function>
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<replaceable>s</replaceable></term>
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<listitem><para>Throw an error message
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<replaceable>s</replaceable>. This usually aborts Nix expression
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evaluation, but in <command>nix-env -qa</command> and other
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commands that try to evaluate a set of derivations to get
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information about those derivations, a derivation that throws an
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error is silently skipped (which is not the case for
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<function>abort</function>).</para></listitem>
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</varlistentry>
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<varlistentry
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xml:id='builtin-toFile'><term><function>builtins.toFile</function>
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<replaceable>name</replaceable> <replaceable>s</replaceable></term>
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@ -582,6 +734,17 @@ stdenv.mkDerivation (rec {
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</varlistentry>
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<varlistentry><term><function>builtins.trace</function>
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<replaceable>e1</replaceable> <replaceable>e2</replaceable></term>
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<listitem><para>Evaluate <replaceable>e1</replaceable> and print its
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abstract syntax representation on standard error. Then return
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<replaceable>e2</replaceable>. This function is useful for
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debugging.</para></listitem>
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</varlistentry>
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</variablelist>
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