Add warning for probable identities (fromIntegral and friends)

[ghc-hetmet.git] / docs / users_guide / using.xml

diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml
index be82322..22c8861 100644 (file)
--- a/docs/users_guide/using.xml
+++ b/docs/users_guide/using.xml
@@ -1175,6 +1175,21 @@ foreign import "&f" f :: FunPtr t
       </varlistentry>
 
       <varlistentry>
+        <term><option>-fwarn-identities</option>:</term>
+       <listitem>
+          <indexterm><primary><option>-fwarn-identities</option></primary></indexterm>
+          <para>Causes the compiler to emit a warning when a Prelude numeric
+            conversion converts a type T to the same type T; such calls
+            are probably no-ops and can be omitted.  The functions checked for
+            are: <literal>toInteger</literal>,
+            <literal>toRational</literal>,
+            <literal>fromIntegral</literal>,
+            and <literal>realToFrac</literal>.
+          </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><option>-fwarn-implicit-prelude</option>:</term>
         <listitem>
           <indexterm><primary><option>-fwarn-implicit-prelude</option></primary></indexterm>