diff options
Diffstat (limited to 'doc/manual/expressions/arguments-variables.xml')
| -rw-r--r-- | doc/manual/expressions/arguments-variables.xml | 114 |
1 files changed, 0 insertions, 114 deletions
diff --git a/doc/manual/expressions/arguments-variables.xml b/doc/manual/expressions/arguments-variables.xml deleted file mode 100644 index a4375c777..000000000 --- a/doc/manual/expressions/arguments-variables.xml +++ /dev/null @@ -1,114 +0,0 @@ -<section xmlns="http://docbook.org/ns/docbook" - xmlns:xlink="http://www.w3.org/1999/xlink" - xmlns:xi="http://www.w3.org/2001/XInclude" - version="5.0" - xml:id='sec-arguments'> - -<title>Arguments and Variables</title> - -<para>The Nix expression in <xref linkend='ex-hello-nix' /> is a -function; it is missing some arguments that have to be filled in -somewhere. In the Nix Packages collection this is done in the file -<filename>pkgs/top-level/all-packages.nix</filename>, where all Nix -expressions for packages are imported and called with the appropriate -arguments. Here are some fragments of -<filename>all-packages.nix</filename>, with annotations of what they -mean:</para> - -<programlisting> -... - -rec { ① - - hello = import ../applications/misc/hello/ex-1 ② { ③ - inherit fetchurl stdenv perl; - }; - - perl = import ../development/interpreters/perl { ④ - inherit fetchurl stdenv; - }; - - fetchurl = import ../build-support/fetchurl { - inherit stdenv; ... - }; - - stdenv = ...; - -} -</programlisting> - -<orderedlist> - - <listitem> - <para>This file defines a set of attributes, all of which are - concrete derivations (i.e., not functions). In fact, we define a - <emphasis>mutually recursive</emphasis> set of attributes. That - is, the attributes can refer to each other. This is precisely - what we want since we want to <quote>plug</quote> the - various packages into each other.</para> - </listitem> - - <listitem> - - <para>Here we <emphasis>import</emphasis> the Nix expression for - GNU Hello. The import operation just loads and returns the - specified Nix expression. In fact, we could just have put the - contents of <xref linkend='ex-hello-nix' /> in - <filename>all-packages.nix</filename> at this point. That - would be completely equivalent, but it would make the file rather - bulky.</para> - - <para>Note that we refer to - <filename>../applications/misc/hello/ex-1</filename>, not - <filename>../applications/misc/hello/ex-1/default.nix</filename>. - When you try to import a directory, Nix automatically appends - <filename>/default.nix</filename> to the file name.</para> - - </listitem> - - <listitem> - - <para>This is where the actual composition takes place. Here we - <emphasis>call</emphasis> the function imported from - <filename>../applications/misc/hello/ex-1</filename> with a set - containing the things that the function expects, namely - <varname>fetchurl</varname>, <varname>stdenv</varname>, and - <varname>perl</varname>. We use inherit again to use the - attributes defined in the surrounding scope (we could also have - written <literal>fetchurl = fetchurl;</literal>, etc.).</para> - - <para>The result of this function call is an actual derivation - that can be built by Nix (since when we fill in the arguments of - the function, what we get is its body, which is the call to - <varname>stdenv.mkDerivation</varname> in <xref - linkend='ex-hello-nix' />).</para> - - <note><para>Nixpkgs has a convenience function - <function>callPackage</function> that imports and calls a - function, filling in any missing arguments by passing the - corresponding attribute from the Nixpkgs set, like this: - -<programlisting> -hello = callPackage ../applications/misc/hello/ex-1 { }; -</programlisting> - - If necessary, you can set or override arguments: - -<programlisting> -hello = callPackage ../applications/misc/hello/ex-1 { stdenv = myStdenv; }; -</programlisting> - - </para></note> - - </listitem> - - <listitem> - - <para>Likewise, we have to instantiate Perl, - <varname>fetchurl</varname>, and the standard environment.</para> - - </listitem> - -</orderedlist> - -</section> |