Add tuple sections as a new feature

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

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 5d1b5cf..43e8439 100644 (file)
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -109,7 +109,7 @@ While you really can use this stuff to write fast code,
 
 <para>All these primitive data types and operations are exported by the 
 library <literal>GHC.Prim</literal>, for which there is 
-<ulink url="../libraries/base/GHC.Prim.html">detailed online documentation</ulink>.
+<ulink url="../libraries/ghc-prim/GHC-Prim.html">detailed online documentation</ulink>.
 (This documentation is generated from the file <filename>compiler/prelude/primops.txt.pp</filename>.)
 </para>
 <para>
@@ -874,7 +874,7 @@ As you can guess <literal>justOnes</literal> will evaluate to <literal>Just [1,1
 </para>
 
 <para>
-The Control.Monad.Fix library introduces the <literal>MonadFix</literal> class. It's definition is:
+The Control.Monad.Fix library introduces the <literal>MonadFix</literal> class.  Its definition is:
 </para>
 <programlisting>
 class Monad m => MonadFix m where
@@ -1001,7 +1001,7 @@ This name is not supported by GHC.
 
 
     <para>Generalised list comprehensions are a further enhancement to the
-    list comprehension syntatic sugar to allow operations such as sorting
+    list comprehension syntactic sugar to allow operations such as sorting
     and grouping which are familiar from SQL.   They are fully described in the
        paper <ulink url="http://research.microsoft.com/~simonpj/papers/list-comp">
          Comprehensive comprehensions: comprehensions with "order by" and "group by"</ulink>,
@@ -1042,7 +1042,7 @@ then f
 </programlisting>
 
     This statement requires that <literal>f</literal> have the type <literal>
-    forall a. [a] -> [a]</literal>. You can see an example of it's use in the
+    forall a. [a] -> [a]</literal>. You can see an example of its use in the
     motivating example, as this form is used to apply <literal>take 5</literal>.
     
     </listitem>
@@ -1269,6 +1269,44 @@ definitions; you must define such a function in prefix form.</para>
 
 </sect2>
 
+<sect2 id="tuple-sections">
+<title>Tuple sections</title>
+
+<para>
+  The <option>-XTupleSections</option> flag enables Python-style partially applied
+  tuple constructors. For example, the following program
+<programlisting>
+  (, True)
+</programlisting>
+  is considered to be an alternative notation for the more unwieldy alternative
+<programlisting>
+  \x -> (x, True)
+</programlisting>
+You can omit any combination of arguments to the tuple, as in the following
+<programlisting>
+  (, "I", , , "Love", , 1337)
+</programlisting>
+which translates to
+<programlisting>
+  \a b c d -> (a, "I", b, c, "Love", d, 1337)
+</programlisting>
+</para>
+
+<para>
+  If you have <link linkend="unboxed-tuples">unboxed tuples</link> enabled, tuple sections
+  will also be available for them, like so
+<programlisting>
+  (# , True #)
+</programlisting>
+Because there is no unboxed unit tuple, the following expression
+<programlisting>
+  (# #)
+</programlisting>
+continues to stand for the unboxed singleton tuple data constructor.
+</para>
+
+</sect2>
+
 <sect2 id="disambiguate-fields">
 <title>Record field disambiguation</title>
 <para>
@@ -2579,7 +2617,7 @@ constructor).
 </para></listitem>
 
 <listitem><para>
-It's is permitted to declare an ordinary algebraic data type using GADT-style syntax.
+It is permitted to declare an ordinary algebraic data type using GADT-style syntax.
 What makes a GADT into a GADT is not the syntax, but rather the presence of data constructors
 whose result type is not just <literal>T a b</literal>.
 </para></listitem>
@@ -4298,7 +4336,7 @@ type family Elem c
       example, consider the following declaration: 
 <programlisting>
 type family F a b :: * -> *   -- F's arity is 2, 
-                              -- although it's overall kind is * -> * -> * -> *
+                              -- although its overall kind is * -> * -> * -> *
 </programlisting>
       Given this declaration the following are examples of well-formed and
       malformed types: