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Diffstat (limited to 'doc/manual/expressions/language-constructs.xml')
| -rw-r--r-- | doc/manual/expressions/language-constructs.xml | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/doc/manual/expressions/language-constructs.xml b/doc/manual/expressions/language-constructs.xml index f961ed921..0d0cbbe15 100644 --- a/doc/manual/expressions/language-constructs.xml +++ b/doc/manual/expressions/language-constructs.xml @@ -43,7 +43,7 @@ encountered</quote>).</para></footnote>.</para> <simplesect xml:id="sect-let-expressions"><title>Let-expressions</title> -<para>A let-expression allows you define local variables for an +<para>A let-expression allows you to define local variables for an expression. For instance, <programlisting> @@ -217,7 +217,25 @@ but can also be written as: ellipsis(<literal>...</literal>) as you can access attribute names as <literal>a</literal>, using <literal>args.a</literal>, which was given as an additional attribute to the function. - </para></listitem> + </para> + + <warning> + <para> + The <literal>args@</literal> expression is bound to the argument passed to the function which + means that attributes with defaults that aren't explicitly specified in the function call + won't cause an evaluation error, but won't exist in <literal>args</literal>. + </para> + <para> + For instance +<programlisting> +let + function = args@{ a ? 23, ... }: args; +in + function {} +</programlisting> + will evaluate to an empty attribute set. + </para> + </warning></listitem> </itemizedlist> |