From 151aaf84ce5b4838f6d1be014681b3135a69b5db Mon Sep 17 00:00:00 2001
From: Brian Anderson <banderson@mozilla.com>
Date: Mon, 31 Oct 2011 15:37:40 -0700
Subject: [PATCH] Add pattern guard docs to language ref

---
 doc/rust.texi | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/doc/rust.texi b/doc/rust.texi
index 2a5a7c89249..724e5086eae 100644
--- a/doc/rust.texi
+++ b/doc/rust.texi
@@ -676,6 +676,7 @@ The keywords are:
 @tab @code{fail}
 @tab @code{ret}
 @tab @code{be}
+@item @code{when}
 @end multitable
 
 @node       Ref.Lex.Res
@@ -3361,6 +3362,18 @@ let message = alt x @{
 @}
 @end example
 
+Finally, alt patterns can accept @emph{pattern guards} to further refine the
+criteria for matching a case. Pattern guards appear after the pattern and
+consist of a bool-typed expression following the @emph{when} keyword. A pattern
+guard may refer to the variables bound within the pattern they follow.
+
+@example
+let message = alt maybe_digit @{
+  some(x) when x < 10 @{ process_digit(x) @}
+  some(x) @{ process_other(x) @}
+@}
+@end example
+
 
 @node          Ref.Expr.Alt.Type
 @subsubsection Ref.Expr.Alt.Type