<option>-fglasgow-exts</option> option. Rather than maintaining
the list of per-file options in a <filename>Makefile</filename>,
it is possible to do this directly in the source file using the
- <literal>OPTIONS</literal> pragma <indexterm><primary>OPTIONS
+ <literal>OPTIONS_GHC</literal> pragma <indexterm><primary>OPTIONS_GHC
pragma</primary></indexterm>:</para>
<programlisting>
-{-# OPTIONS -fglasgow-exts #-}
+{-# OPTIONS_GHC -fglasgow-exts #-}
module X where
...
</programlisting>
- <para><literal>OPTIONS</literal> pragmas are only looked for at
+ <para><literal>OPTIONS_GHC</literal> pragmas are only looked for at
the top of your source files, upto the first
(non-literate,non-empty) line not containing
- <literal>OPTIONS</literal>. Multiple <literal>OPTIONS</literal>
- pragmas are recognised. Note that your command shell does not
+ <literal>OPTIONS_GHC</literal>. Multiple <literal>OPTIONS_GHC</literal>
+ pragmas are recognised. Do not put comments before, or on the same line
+ as, the <literal>OPTIONS_GHC</literal> pragma.</para>
+
+ <para>Note that your command shell does not
get to the source file options, they are just included literally
- in the array of command-line arguments the compiler driver
+ in the array of command-line arguments the compiler
maintains internally, so you'll be desperately disappointed if
- you try to glob etc. inside <literal>OPTIONS</literal>.</para>
+ you try to glob etc. inside <literal>OPTIONS_GHC</literal>.</para>
- <para>NOTE: the contents of OPTIONS are prepended to the
+ <para>NOTE: the contents of OPTIONS_GHC are prepended to the
command-line options, so you <emphasis>do</emphasis> have the
- ability to override OPTIONS settings via the command
+ ability to override OPTIONS_GHC settings via the command
line.</para>
<para>It is not recommended to move all the contents of your
Makefiles into your source files, but in some circumstances, the
- <literal>OPTIONS</literal> pragma is the Right Thing. (If you
+ <literal>OPTIONS_GHC</literal> pragma is the Right Thing. (If you
use <option>-keep-hc-file-too</option> and have OPTION flags in
- your module, the OPTIONS will get put into the generated .hc
+ your module, the OPTIONS_GHC will get put into the generated .hc
file).</para>
</sect2>
<para>Each of GHC's command line options is classified as either
<firstterm>static</firstterm> or <firstterm>dynamic</firstterm>.
A static flag may only be specified on the command line, whereas a
- dynamic flag may also be given in an <literal>OPTIONS</literal>
+ dynamic flag may also be given in an <literal>OPTIONS_GHC</literal>
pragma in a source file or set from the GHCi command-line with
<literal>:set</literal>.</para>
<option>––make</option>, but note that any options
you give on the command line will apply to all the source files
compiled, so if you want any options to apply to a single source
- file only, you'll need to use an <literal>OPTIONS</literal>
+ file only, you'll need to use an <literal>OPTIONS_GHC</literal>
pragma (see <xref linkend="source-file-options"/>).</para>
<para>If the program needs to be linked with additional objects
</varlistentry>
<varlistentry>
+ <term><option>-fwarn-incomplete-record-updates</option>:</term>
+ <listitem>
+ <indexterm><primary><option>-fwarn-incomplete-record-updates</option></primary></indexterm>
+ <indexterm><primary>incomplete record updates, warning</primary></indexterm>
+ <indexterm><primary>record updates, incomplete</primary></indexterm>
+
+ <para>The function
+ <function>f</function> below will fail when applied to
+ <literal>Bar</literal>, so the compiler will emit a warning about
+ this when <option>-fwarn-incomplete-record-updates</option> is
+ enabled.</para>
+
+<programlisting>
+data Foo = Foo { x :: Int }
+ | Bar
+
+f :: Foo -> Foo
+f foo = foo { x = 6 }
+</programlisting>
+
+ <para>This option isn't enabled be default because it can be
+ very noisy, and it often doesn't indicate a bug in the
+ program.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term>
<option>-fwarn-misc</option>:
<indexterm><primary><option>-fwarn-misc</option></primary></indexterm>
</varlistentry>
<varlistentry>
+ <term><option>-fwarn-orphans</option>:</term>
+ <listitem>
+ <indexterm><primary><option>-fwarn-orphans</option></primary></indexterm>
+ <indexterm><primary>orphan instances, warning</primary></indexterm>
+ <indexterm><primary>orphan rules, warning</primary></indexterm>
+
+ <para>This option causes a warning to be emitted whenever the
+ module contains an "orphan" instance declaration or rewrite rule.
+ An instance declartion is an orphan if it appears in a module in
+ which neither the class nor the type being instanced are declared
+ in the same module. A rule is an orphan if it is a rule for a
+ function declared in another module. A module containing any
+ orphans is called an orphan module.</para>
+ <para>The trouble with orphans is that GHC must pro-actively read the interface
+ files for all orphan modules, just in case their instances or rules
+ play a role, whether or not the module's interface would otherwise
+ be of any use. Other things being equal, avoid orphan modules.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term>
<option>-fwarn-overlapping-patterns</option>:
<indexterm><primary><option>-fwarn-overlapping-patterns</option></primary></indexterm>
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