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4 files changed, 182 insertions, 102 deletions
diff --git a/nixos/doc/manual/configuration/abstractions.section.md b/nixos/doc/manual/configuration/abstractions.section.md new file mode 100644 index 00000000000..bf26e4c51ed --- /dev/null +++ b/nixos/doc/manual/configuration/abstractions.section.md @@ -0,0 +1,80 @@ +# Abstractions {#sec-module-abstractions} + +If you find yourself repeating yourself over and over, it’s time to abstract. Take, for instance, this Apache HTTP Server configuration: + +```nix +{ + services.httpd.virtualHosts = + { "blog.example.org" = { + documentRoot = "/webroot/blog.example.org"; + adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + enablePHP = true; + }; + "wiki.example.org" = { + documentRoot = "/webroot/wiki.example.org"; + adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + enablePHP = true; + }; + }; +} +``` + +It defines two virtual hosts with nearly identical configuration; the only difference is the document root directories. To prevent this duplication, we can use a `let`: +```nix +let + commonConfig = + { adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + }; +in +{ + services.httpd.virtualHosts = + { "blog.example.org" = (commonConfig // { documentRoot = "/webroot/blog.example.org"; }); + "wiki.example.org" = (commonConfig // { documentRoot = "/webroot/wiki.example.com"; }); + }; +} +``` + +The `let commonConfig = ...` defines a variable named `commonConfig`. The `//` operator merges two attribute sets, so the configuration of the second virtual host is the set `commonConfig` extended with the document root option. + +You can write a `let` wherever an expression is allowed. Thus, you also could have written: + +```nix +{ + services.httpd.virtualHosts = + let commonConfig = ...; in + { "blog.example.org" = (commonConfig // { ... }) + "wiki.example.org" = (commonConfig // { ... }) + }; +} +``` + +but not `{ let commonConfig = ...; in ...; }` since attributes (as opposed to attribute values) are not expressions. + +**Functions** provide another method of abstraction. For instance, suppose that we want to generate lots of different virtual hosts, all with identical configuration except for the document root. This can be done as follows: + +```nix +{ + services.httpd.virtualHosts = + let + makeVirtualHost = webroot: + { documentRoot = webroot; + adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + }; + in + { "example.org" = (makeVirtualHost "/webroot/example.org"); + "example.com" = (makeVirtualHost "/webroot/example.com"); + "example.gov" = (makeVirtualHost "/webroot/example.gov"); + "example.nl" = (makeVirtualHost "/webroot/example.nl"); + }; +} +``` + +Here, `makeVirtualHost` is a function that takes a single argument `webroot` and returns the configuration for a virtual host. That function is then called for several names to produce the list of virtual host configurations. diff --git a/nixos/doc/manual/configuration/abstractions.xml b/nixos/doc/manual/configuration/abstractions.xml deleted file mode 100644 index df9ff2615e1..00000000000 --- a/nixos/doc/manual/configuration/abstractions.xml +++ /dev/null @@ -1,101 +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-module-abstractions"> - <title>Abstractions</title> - - <para> - If you find yourself repeating yourself over and over, it’s time to - abstract. Take, for instance, this Apache HTTP Server configuration: -<programlisting> -{ - <xref linkend="opt-services.httpd.virtualHosts"/> = - { "blog.example.org" = { - documentRoot = "/webroot/blog.example.org"; - adminAddr = "alice@example.org"; - forceSSL = true; - enableACME = true; - enablePHP = true; - }; - "wiki.example.org" = { - documentRoot = "/webroot/wiki.example.org"; - adminAddr = "alice@example.org"; - forceSSL = true; - enableACME = true; - enablePHP = true; - }; - }; -} -</programlisting> - It defines two virtual hosts with nearly identical configuration; the only - difference is the document root directories. To prevent this - duplication, we can use a <literal>let</literal>: -<programlisting> -let - commonConfig = - { adminAddr = "alice@example.org"; - forceSSL = true; - enableACME = true; - }; -in -{ - <xref linkend="opt-services.httpd.virtualHosts"/> = - { "blog.example.org" = (commonConfig // { documentRoot = "/webroot/blog.example.org"; }); - "wiki.example.org" = (commonConfig // { documentRoot = "/webroot/wiki.example.com"; }); - }; -} -</programlisting> - The <literal>let commonConfig = <replaceable>...</replaceable></literal> - defines a variable named <literal>commonConfig</literal>. The - <literal>//</literal> operator merges two attribute sets, so the - configuration of the second virtual host is the set - <literal>commonConfig</literal> extended with the document root option. - </para> - - <para> - You can write a <literal>let</literal> wherever an expression is allowed. - Thus, you also could have written: -<programlisting> -{ - <xref linkend="opt-services.httpd.virtualHosts"/> = - let commonConfig = <replaceable>...</replaceable>; in - { "blog.example.org" = (commonConfig // { <replaceable>...</replaceable> }) - "wiki.example.org" = (commonConfig // { <replaceable>...</replaceable> }) - }; -} -</programlisting> - but not <literal>{ let commonConfig = <replaceable>...</replaceable>; in - <replaceable>...</replaceable>; }</literal> since attributes (as opposed to - attribute values) are not expressions. - </para> - - <para> - <emphasis>Functions</emphasis> provide another method of abstraction. For - instance, suppose that we want to generate lots of different virtual hosts, - all with identical configuration except for the document root. This can be done - as follows: -<programlisting> -{ - <xref linkend="opt-services.httpd.virtualHosts"/> = - let - makeVirtualHost = webroot: - { documentRoot = webroot; - adminAddr = "alice@example.org"; - forceSSL = true; - enableACME = true; - }; - in - { "example.org" = (makeVirtualHost "/webroot/example.org"); - "example.com" = (makeVirtualHost "/webroot/example.com"); - "example.gov" = (makeVirtualHost "/webroot/example.gov"); - "example.nl" = (makeVirtualHost "/webroot/example.nl"); - }; -} -</programlisting> - Here, <varname>makeVirtualHost</varname> is a function that takes a single - argument <literal>webroot</literal> and returns the configuration for a virtual - host. That function is then called for several names to produce the list of - virtual host configurations. - </para> -</section> diff --git a/nixos/doc/manual/configuration/config-syntax.xml b/nixos/doc/manual/configuration/config-syntax.xml index 5526dea247c..a374c6a8707 100644 --- a/nixos/doc/manual/configuration/config-syntax.xml +++ b/nixos/doc/manual/configuration/config-syntax.xml @@ -19,7 +19,7 @@ xlink:href="https://nixos.org/nix/manual/#chap-writing-nix-expressions">Nix constructs useful in NixOS configuration files. </para> <xi:include href="config-file.xml" /> - <xi:include href="abstractions.xml" /> + <xi:include href="../from_md/configuration/abstractions.section.xml" /> <xi:include href="modularity.xml" /> <xi:include href="summary.xml" /> </chapter> diff --git a/nixos/doc/manual/from_md/configuration/abstractions.section.xml b/nixos/doc/manual/from_md/configuration/abstractions.section.xml new file mode 100644 index 00000000000..c71e23e34ad --- /dev/null +++ b/nixos/doc/manual/from_md/configuration/abstractions.section.xml @@ -0,0 +1,101 @@ +<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-module-abstractions"> + <title>Abstractions</title> + <para> + If you find yourself repeating yourself over and over, it’s time to + abstract. Take, for instance, this Apache HTTP Server configuration: + </para> + <programlisting language="bash"> +{ + services.httpd.virtualHosts = + { "blog.example.org" = { + documentRoot = "/webroot/blog.example.org"; + adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + enablePHP = true; + }; + "wiki.example.org" = { + documentRoot = "/webroot/wiki.example.org"; + adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + enablePHP = true; + }; + }; +} +</programlisting> + <para> + It defines two virtual hosts with nearly identical configuration; + the only difference is the document root directories. To prevent + this duplication, we can use a <literal>let</literal>: + </para> + <programlisting language="bash"> +let + commonConfig = + { adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + }; +in +{ + services.httpd.virtualHosts = + { "blog.example.org" = (commonConfig // { documentRoot = "/webroot/blog.example.org"; }); + "wiki.example.org" = (commonConfig // { documentRoot = "/webroot/wiki.example.com"; }); + }; +} +</programlisting> + <para> + The <literal>let commonConfig = ...</literal> defines a variable + named <literal>commonConfig</literal>. The <literal>//</literal> + operator merges two attribute sets, so the configuration of the + second virtual host is the set <literal>commonConfig</literal> + extended with the document root option. + </para> + <para> + You can write a <literal>let</literal> wherever an expression is + allowed. Thus, you also could have written: + </para> + <programlisting language="bash"> +{ + services.httpd.virtualHosts = + let commonConfig = ...; in + { "blog.example.org" = (commonConfig // { ... }) + "wiki.example.org" = (commonConfig // { ... }) + }; +} +</programlisting> + <para> + but not <literal>{ let commonConfig = ...; in ...; }</literal> since + attributes (as opposed to attribute values) are not expressions. + </para> + <para> + <emphasis role="strong">Functions</emphasis> provide another method + of abstraction. For instance, suppose that we want to generate lots + of different virtual hosts, all with identical configuration except + for the document root. This can be done as follows: + </para> + <programlisting language="bash"> +{ + services.httpd.virtualHosts = + let + makeVirtualHost = webroot: + { documentRoot = webroot; + adminAddr = "alice@example.org"; + forceSSL = true; + enableACME = true; + }; + in + { "example.org" = (makeVirtualHost "/webroot/example.org"); + "example.com" = (makeVirtualHost "/webroot/example.com"); + "example.gov" = (makeVirtualHost "/webroot/example.gov"); + "example.nl" = (makeVirtualHost "/webroot/example.nl"); + }; +} +</programlisting> + <para> + Here, <literal>makeVirtualHost</literal> is a function that takes a + single argument <literal>webroot</literal> and returns the + configuration for a virtual host. That function is then called for + several names to produce the list of virtual host configurations. + </para> +</section> |