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Diffstat (limited to 'doc/manual/writing-nix-expressions.xml')
| -rw-r--r-- | doc/manual/writing-nix-expressions.xml | 106 |
1 files changed, 53 insertions, 53 deletions
diff --git a/doc/manual/writing-nix-expressions.xml b/doc/manual/writing-nix-expressions.xml index 5ba3df56c7c9..4154926268e0 100644 --- a/doc/manual/writing-nix-expressions.xml +++ b/doc/manual/writing-nix-expressions.xml @@ -118,10 +118,10 @@ the single Nix expression in that directory <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>. An attribute set is just a list - of key/value pairs where each value is an arbitrary Nix - expression. They take the general form - <literal>{ <replaceable>name1</replaceable> = + <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> @@ -384,9 +384,9 @@ some fragments of <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 an - attribute set containing the things that the function expects, - namely <varname>fetchurl</varname>, <varname>stdenv</varname>, and + <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> @@ -805,20 +805,21 @@ to be enclosed in parentheses. If they had been omitted, e.g., [ 123 ./foo.nix "abc" f { x = y; } ]</programlisting> the result would be a list of five elements, the fourth one being a -function and the fifth being an attribute set.</para> +function and the fifth being a set.</para> </simplesect> -<simplesect><title>Attribute sets</title> +<simplesect><title>Sets</title> -<para>Attribute sets are really the core of the language, since -ultimately it's all about creating derivations, which are really just +<para>Sets are really the core of the language, since ultimately the +Nix language is all about creating derivations, which are really just sets of attributes to be passed to build scripts.</para> -<para>Attribute sets are just a list of name/value pairs enclosed in -curly brackets, where each value is an arbitrary expression terminated -by a semicolon. For example: +<para>Sets are just a list of name/value pairs (called +<emphasis>attributes</emphasis>) enclosed in curly brackets, where +each value is an arbitrary expression terminated by a semicolon. For +example: <programlisting> { x = 123; @@ -826,12 +827,12 @@ by a semicolon. For example: y = f { bla = 456; }; }</programlisting> -This defines an attribute set with attributes named -<varname>x</varname>, <varname>text</varname>, <varname>y</varname>. -The order of the attributes is irrelevant. An attribute name may only -occur once.</para> +This defines a set with attributes named <varname>x</varname>, +<varname>text</varname>, <varname>y</varname>. The order of the +attributes is irrelevant. An attribute name may only occur +once.</para> -<para>Attributes can be selected from an attribute set using the +<para>Attributes can be selected from a set using the <literal>.</literal> operator. For instance, <programlisting> @@ -864,10 +865,10 @@ This will evaluate to <literal>123</literal>.</para> <section><title>Language constructs</title> -<simplesect><title>Recursive attribute sets</title> +<simplesect><title>Recursive sets</title> -<para>Recursive attribute sets are just normal attribute sets, but the -attributes can refer to each other. For example, +<para>Recursive sets are just normal sets, but the attributes can +refer to each other. For example, <programlisting> rec { @@ -880,11 +881,11 @@ evaluates to <literal>123</literal>. Note that without <literal>rec</literal> the binding <literal>x = y;</literal> would refer to the variable <varname>y</varname> in the surrounding scope, if one exists, and would be invalid if no such variable exists. That -is, in a normal (non-recursive) attribute set, attributes are not -added to the lexical scope; in a recursive set, they are.</para> +is, in a normal (non-recursive) set, attributes are not added to the +lexical scope; in a recursive set, they are.</para> -<para>Recursive attribute sets of course introduce the danger of -infinite recursion. For example, +<para>Recursive sets of course introduce the danger of infinite +recursion. For example, <programlisting> rec { @@ -918,16 +919,16 @@ evaluates to <literal>"foobar"</literal>. <literal>let { <replaceable>attrs</replaceable> }</literal>, which is translated to <literal>rec { <replaceable>attrs</replaceable> }.body</literal>. That is, the body of the let-expression is the -<literal>body</literal> attribute of the attribute set.</para></note> +<literal>body</literal> attribute of the set.</para></note> </simplesect> <simplesect><title>Inheriting attributes</title> -<para>When defining an attribute set it is often convenient to copy -variables from the surrounding lexical scope (e.g., when you want to -propagate attributes). This can be shortened using the +<para>When defining a set it is often convenient to copy variables +from the surrounding lexical scope (e.g., when you want to propagate +attributes). This can be shortened using the <literal>inherit</literal> keyword. For instance, <programlisting> @@ -936,10 +937,10 @@ let x = 123; in y = 456; }</programlisting> -evaluates to <literal>{ x = 123; y = 456; }</literal>. (Note that this -works because <varname>x</varname> is added to the lexical scope by -the <literal>let</literal> construct.) It is also possible to inherit -attributes from another attribute set. For instance, in this fragment +evaluates to <literal>{ x = 123; y = 456; }</literal>. (Note that +this works because <varname>x</varname> is added to the lexical scope +by the <literal>let</literal> construct.) It is also possible to +inherit attributes from another set. For instance, in this fragment from <filename>all-packages.nix</filename>, <programlisting> @@ -958,13 +959,12 @@ from <filename>all-packages.nix</filename>, libjpg = ...; ...</programlisting> -the attribute set used in the function call to the function defined in +the set used in the function call to the function defined in <filename>../tools/graphics/graphviz</filename> inherits a number of variables from the surrounding scope (<varname>fetchurl</varname> ... <varname>yacc</varname>), but also inherits <varname>libXaw</varname> (the X Athena Widgets) from the -<varname>xlibs</varname> (X11 client-side libraries) attribute -set.</para> +<varname>xlibs</varname> (X11 client-side libraries) set.</para> </simplesect> @@ -1003,11 +1003,11 @@ map (concat "foo") [ "bar" "bla" "abc" ]</programlisting> "fooabc" ]</literal>.</para></listitem> - <listitem><para>An <emphasis>attribute set pattern</emphasis> of the - form <literal>{ name1, name2, …, nameN }</literal> - matches an attribute set containing the listed attributes, and binds - the values of those attributes to variables in the function body. - For example, the function + <listitem><para>A <emphasis>set pattern</emphasis> of the form + <literal>{ name1, name2, …, nameN }</literal> matches a set + containing the listed attributes, and binds the values of those + attributes to variables in the function body. For example, the + function <programlisting> { x, y, z }: z + y + x</programlisting> @@ -1174,9 +1174,8 @@ used in the Nix expression for Subversion.</para> <programlisting> with <replaceable>e1</replaceable>; <replaceable>e2</replaceable></programlisting> -introduces the attribute set <replaceable>e1</replaceable> into the -lexical scope of the expression <replaceable>e2</replaceable>. For -instance, +introduces the set <replaceable>e1</replaceable> into the lexical +scope of the expression <replaceable>e2</replaceable>. For instance, <programlisting> let as = { x = "foo"; y = "bar"; }; @@ -1235,7 +1234,7 @@ weakest binding).</para> </entry> <entry>none</entry> <entry>Select attribute denoted by the attribute path - <replaceable>attrpath</replaceable> from attribute set + <replaceable>attrpath</replaceable> from set <replaceable>e</replaceable>. (An attribute path is a dot-separated list of attribute names.) If the attribute doesn’t exist, return <replaceable>def</replaceable> if @@ -1251,8 +1250,8 @@ weakest binding).</para> <entry><replaceable>e</replaceable> <literal>?</literal> <replaceable>attrpath</replaceable></entry> <entry>none</entry> - <entry>Test whether attribute set <replaceable>e</replaceable> - contains the attribute denoted by <replaceable>attrpath</replaceable>; + <entry>Test whether set <replaceable>e</replaceable> contains + the attribute denoted by <replaceable>attrpath</replaceable>; return <literal>true</literal> or <literal>false</literal>.</entry> </row> @@ -1275,10 +1274,11 @@ weakest binding).</para> <entry><replaceable>e1</replaceable> <literal>//</literal> <replaceable>e2</replaceable></entry> <entry>right</entry> - <entry>Return an attribute set consisting of the attributes in + <entry>Return a set consisting of the attributes in <replaceable>e1</replaceable> and <replaceable>e2</replaceable> (with the latter taking - precedence over the former in case of equally named attributes).</entry> + precedence over the former in case of equally named + attributes).</entry> </row> <row> <entry><replaceable>e1</replaceable> <literal>==</literal> @@ -1322,9 +1322,9 @@ weakest binding).</para> <section xml:id="ssec-derivation"><title>Derivations</title> <para>The most important built-in function is -<function>derivation</function>, which is used to describe a -single derivation (a build action). It takes as input an attribute -set, the attributes of which specify the inputs of the build.</para> +<function>derivation</function>, which is used to describe a single +derivation (a build action). It takes as input a set, the attributes +of which specify the inputs of the build.</para> <itemizedlist> |