---

yaml
---
r: 6067
b: refs/heads/master
c: 151aaf8
h: refs/heads/master
i:
  6065: fce5bb3
  6063: a7b6461
v: v3

Author: brson

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 93035722a47915793c75af79af8f39c9840a78c0
+refs/heads/master: 151aaf84ce5b4838f6d1be014681b3135a69b5db

trunk/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