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diff --git a/doc/manual/expressions/expression-syntax.xml b/doc/manual/expressions/expression-syntax.xml deleted file mode 100644 index a3de20713..000000000 --- a/doc/manual/expressions/expression-syntax.xml +++ /dev/null @@ -1,148 +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-expression-syntax'> - -<title>Expression Syntax</title> - -<example xml:id='ex-hello-nix'><title>Nix expression for GNU Hello -(<filename>default.nix</filename>)</title> -<programlisting> -{ stdenv, fetchurl, perl }: <co xml:id='ex-hello-nix-co-1' /> - -stdenv.mkDerivation { <co xml:id='ex-hello-nix-co-2' /> - name = "hello-2.1.1"; <co xml:id='ex-hello-nix-co-3' /> - builder = ./builder.sh; <co xml:id='ex-hello-nix-co-4' /> - src = fetchurl { <co xml:id='ex-hello-nix-co-5' /> - url = "ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz"; - sha256 = "1md7jsfd8pa45z73bz1kszpp01yw6x5ljkjk2hx7wl800any6465"; - }; - inherit perl; <co xml:id='ex-hello-nix-co-6' /> -}</programlisting> -</example> - -<para><xref linkend='ex-hello-nix' /> shows a Nix expression for GNU -Hello. It's actually already in the Nix Packages collection in -<filename>pkgs/applications/misc/hello/ex-1/default.nix</filename>. -It is customary to place each package in a separate directory and call -the single Nix expression in that directory -<filename>default.nix</filename>. The file has the following elements -(referenced from the figure by number): - -<calloutlist> - - <callout arearefs='ex-hello-nix-co-1'> - - <para>This states that the expression is a - <emphasis>function</emphasis> that expects to be called with three - arguments: <varname>stdenv</varname>, <varname>fetchurl</varname>, - and <varname>perl</varname>. They are needed to build Hello, but - we don't know how to build them here; that's why they are function - arguments. <varname>stdenv</varname> is a package that is used - by almost all Nix Packages packages; it provides a - <quote>standard</quote> environment consisting of the things you - would expect in a basic Unix environment: a C/C++ compiler (GCC, - to be precise), the Bash shell, fundamental Unix tools such as - <command>cp</command>, <command>grep</command>, - <command>tar</command>, etc. <varname>fetchurl</varname> is a - function that downloads files. <varname>perl</varname> is the - Perl interpreter.</para> - - <para>Nix functions generally have the form <literal>{ x, y, ..., - z }: e</literal> where <varname>x</varname>, <varname>y</varname>, - etc. are the names of the expected arguments, and where - <replaceable>e</replaceable> is the body of the function. So - here, the entire remainder of the file is the body of the - function; when given the required arguments, the body should - describe how to build an instance of the Hello package.</para> - - </callout> - - <callout arearefs='ex-hello-nix-co-2'> - - <para>So we have to build a package. Building something from - other stuff is called a <emphasis>derivation</emphasis> in Nix (as - opposed to sources, which are built by humans instead of - computers). We perform a derivation by calling - <varname>stdenv.mkDerivation</varname>. - <varname>mkDerivation</varname> is a function provided by - <varname>stdenv</varname> that builds a package from a set of - <emphasis>attributes</emphasis>. A set is just a list of - key/value pairs where each key is a string and each value is an - arbitrary Nix expression. They take the general form <literal>{ - <replaceable>name1</replaceable> = - <replaceable>expr1</replaceable>; <replaceable>...</replaceable> - <replaceable>nameN</replaceable> = - <replaceable>exprN</replaceable>; }</literal>.</para> - - </callout> - - <callout arearefs='ex-hello-nix-co-3'> - - <para>The attribute <varname>name</varname> specifies the symbolic - name and version of the package. Nix doesn't really care about - these things, but they are used by for instance <command>nix-env - -q</command> to show a <quote>human-readable</quote> name for - packages. This attribute is required by - <varname>mkDerivation</varname>.</para> - - </callout> - - <callout arearefs='ex-hello-nix-co-4'> - - <para>The attribute <varname>builder</varname> specifies the - builder. This attribute can sometimes be omitted, in which case - <varname>mkDerivation</varname> will fill in a default builder - (which does a <literal>configure; make; make install</literal>, in - essence). Hello is sufficiently simple that the default builder - would suffice, but in this case, we will show an actual builder - for educational purposes. The value - <command>./builder.sh</command> refers to the shell script shown - in <xref linkend='ex-hello-builder' />, discussed below.</para> - - </callout> - - <callout arearefs='ex-hello-nix-co-5'> - - <para>The builder has to know what the sources of the package - are. Here, the attribute <varname>src</varname> is bound to the - result of a call to the <command>fetchurl</command> function. - Given a URL and a SHA-256 hash of the expected contents of the file - at that URL, this function builds a derivation that downloads the - file and checks its hash. So the sources are a dependency that - like all other dependencies is built before Hello itself is - built.</para> - - <para>Instead of <varname>src</varname> any other name could have - been used, and in fact there can be any number of sources (bound - to different attributes). However, <varname>src</varname> is - customary, and it's also expected by the default builder (which we - don't use in this example).</para> - - </callout> - - <callout arearefs='ex-hello-nix-co-6'> - - <para>Since the derivation requires Perl, we have to pass the - value of the <varname>perl</varname> function argument to the - builder. All attributes in the set are actually passed as - environment variables to the builder, so declaring an attribute - - <programlisting> -perl = perl;</programlisting> - - will do the trick: it binds an attribute <varname>perl</varname> - to the function argument which also happens to be called - <varname>perl</varname>. However, it looks a bit silly, so there - is a shorter syntax. The <literal>inherit</literal> keyword - causes the specified attributes to be bound to whatever variables - with the same name happen to be in scope.</para> - - </callout> - -</calloutlist> - -</para> - -</section> |