diff options
Diffstat (limited to 'doc/manual')
| -rw-r--r-- | doc/manual/builtins.xml | 165 |
1 files changed, 164 insertions, 1 deletions
diff --git a/doc/manual/builtins.xml b/doc/manual/builtins.xml index 8f9272505c..1ce40a6076 100644 --- a/doc/manual/builtins.xml +++ b/doc/manual/builtins.xml @@ -1,5 +1,6 @@ <section xmlns="http://docbook.org/ns/docbook" - xmlns:xlink="http://www.w3.org/1999/xlink"> + xmlns:xlink="http://www.w3.org/1999/xlink" + xml:id='ssec-builtins'> <title>Built-in functions</title> @@ -145,6 +146,58 @@ if builtins ? getEnv then __getEnv "PATH" else ""</programlisting> </varlistentry> + <varlistentry><term><function>builtins.filterSource</function> + <replaceable>e1</replaceable> <replaceable>e2</replaceable></term> + + <listitem> + + <para>This function allows you to copy sources into the Nix + store while filtering certain files. For instance, suppose that + you want to use the directory <filename>source-dir</filename> as + an input to a Nix expression, e.g. + +<programlisting> +stdenv.mkDerivation { + ... + src = ./source-dir; +} +</programlisting> + + However, if <filename>source-dir</filename> is a Subversion + working copy, then all those annoying <filename>.svn</filename> + subdirectories will also be copied to the store. Worse, the + contents of those directories may change a lot, causing lots of + spurious rebuilds. With <function>filterSource</function> you + can filter out the <filename>.svn</filename> directories: + +<programlisting> + src = builtins.filterSource + (path: type: type != "directory" || baseNameOf path != ".svn") + ./source-dir; +</programlisting> + + </para> + + <para>Thus, the first argument <replaceable>e1</replaceable> + must be a predicate function that is called for each regular + file, directory or symlink in the source tree + <replaceable>e2</replaceable>. If the function returns + <literal>true</literal>, the file is copied to the Nix store, + otherwise it is omitted. The function is called with two + arguments. The first is the full path of the file. The second + is a string that identifies the type of the file, which is + either <literal>"regular"</literal>, + <literal>"directory"</literal>, <literal>"symlink"</literal> or + <literal>"unknown"</literal> (for other kinds of files such as + device nodes or fifos — but note that those cannot be copied to + the Nix store, so if the predicate returns + <literal>true</literal> for them, the copy will fail).</para> + + </listitem> + + </varlistentry> + + <varlistentry><term><function>builtins.getAttr</function> <replaceable>s</replaceable> <replaceable>attrs</replaceable></term> @@ -254,6 +307,16 @@ x: x + 456</programlisting> </varlistentry> + <varlistentry><term><function>builtins.isAttrs</function> + <replaceable>e</replaceable></term> + + <listitem><para>Return <literal>true</literal> if + <replaceable>e</replaceable> evaluates to an attribute set, and + <literal>false</literal> otherwise.</para></listitem> + + </varlistentry> + + <varlistentry><term><function>builtins.isList</function> <replaceable>e</replaceable></term> @@ -264,6 +327,16 @@ x: x + 456</programlisting> </varlistentry> + <varlistentry><term><function>builtins.isFunction</function> + <replaceable>e</replaceable></term> + + <listitem><para>Return <literal>true</literal> if + <replaceable>e</replaceable> evaluates to a function, and + <literal>false</literal> otherwise.</para></listitem> + + </varlistentry> + + <varlistentry><term><function>isNull</function> <replaceable>e</replaceable></term> @@ -292,6 +365,33 @@ x: x + 456</programlisting> </varlistentry> + <varlistentry><term><function>builtins.listToAttrs</function> + <replaceable>e</replaceable></term> + + <listitem><para>Construct an attribute set from a list specifying + the names and values of each attribute. Each element of the list + should be an attribute set consisting of a string-valued attribute + <varname>name</varname> specifying the name of the attribute, and + an attribute <varname>value</varname> specifying its value. + Example: + +<programlisting> +builtins.listToAttrs [ + {name = "foo"; value = 123;} + {name = "bar"; value = 456;} +] +</programlisting> + + evaluates to + +<programlisting> +{ foo = 123; bar = 456; } +</programlisting> + + </para></listitem> + + </varlistentry> + <varlistentry><term><function>map</function> <replaceable>f</replaceable> <replaceable>list</replaceable></term> @@ -357,6 +457,44 @@ removeAttrs { x = 1; y = 2; z = 3; } ["a" "x" "z"]</screen> </varlistentry> + <varlistentry><term><function>builtins.stringLength</function> + <replaceable>e</replaceable></term> + + <listitem><para>Return the length of the string + <replaceable>e</replaceable>. If <replaceable>e</replaceable> is + not a string, evaluation is aborted.</para></listitem> + + </varlistentry> + + + <varlistentry><term><function>builtins.sub</function> + <replaceable>e1</replaceable> <replaceable>e2</replaceable></term> + + <listitem><para>Return the difference between the integers + <replaceable>e1</replaceable> and + <replaceable>e2</replaceable>.</para></listitem> + + </varlistentry> + + + <varlistentry><term><function>builtins.substr</function> + <replaceable>start</replaceable> <replaceable>len</replaceable> + <replaceable>s</replaceable></term> + + <listitem><para>Return the substring of + <replaceable>s</replaceable> from character position + <replaceable>start</replaceable> (zero-based) up to but not + including <replaceable>start + len</replaceable>. If + <replaceable>start</replaceable> is greater than the length of the + string, an empty string is returned, and if <replaceable>start + + len</replaceable> lies beyond the end of the string, only the + substring up to the end of the string is returned. + <replaceable>start</replaceable> must be + non-negative.</para></listitem> + + </varlistentry> + + <varlistentry><term><function>builtins.tail</function> <replaceable>list</replaceable></term> @@ -367,6 +505,20 @@ removeAttrs { x = 1; y = 2; z = 3; } ["a" "x" "z"]</screen> </varlistentry> + <varlistentry><term><function>throw</function> + <replaceable>s</replaceable></term> + + <listitem><para>Throw an error message + <replaceable>s</replaceable>. This usually aborts Nix expression + evaluation, but in <command>nix-env -qa</command> and other + commands that try to evaluate a set of derivations to get + information about those derivations, a derivation that throws an + error is silently skipped (which is not the case for + <function>abort</function>).</para></listitem> + + </varlistentry> + + <varlistentry xml:id='builtin-toFile'><term><function>builtins.toFile</function> <replaceable>name</replaceable> <replaceable>s</replaceable></term> @@ -582,6 +734,17 @@ stdenv.mkDerivation (rec { </varlistentry> + <varlistentry><term><function>builtins.trace</function> + <replaceable>e1</replaceable> <replaceable>e2</replaceable></term> + + <listitem><para>Evaluate <replaceable>e1</replaceable> and print its + abstract syntax representation on standard error. Then return + <replaceable>e2</replaceable>. This function is useful for + debugging.</para></listitem> + + </varlistentry> + + </variablelist> |