Nothing -> fail
Just val2 -> val1 + val2
where
- fail = val1 + val2
+ fail = var1 + var2
</programlisting>
<para>
</primary></indexterm>
and <option>-fallow-incoherent-instances</option>
<indexterm><primary>-fallow-incoherent-instances
-</primary></indexterm>, as this section discusses.</para>
+</primary></indexterm>, as this section discusses. Both these
+flags are dynamic flags, and can be set on a per-module basis, using
+an <literal>OPTIONS_GHC</literal> pragma if desired (<xref linkend="source-file-options"/>).</para>
<para>
When GHC tries to resolve, say, the constraint <literal>C Int Bool</literal>,
it tries to match every instance declaration against the