Repository : ssh://g...@git.haskell.org/ghc
On branch : master
Link :
http://ghc.haskell.org/trac/ghc/changeset/d2013e85976cccde6c915211f8bcc26f2dc93e33/ghc
>---------------------------------------------------------------
commit d2013e85976cccde6c915211f8bcc26f2dc93e33
Author: Simon Marlow <marlo...@gmail.com>
Date: Tue Oct 8 19:29:21 2013 +0100
docs for new layout behaviour with MultiWayIf (#7783)
>---------------------------------------------------------------
d2013e85976cccde6c915211f8bcc26f2dc93e33
docs/users_guide/glasgow_exts.xml | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/docs/users_guide/glasgow_exts.xml
b/docs/users_guide/glasgow_exts.xml
index 92305f2..2a6c818 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -1770,7 +1770,35 @@ which is roughly equivalent to
...
_ | guardN -> exprN
</programlisting>
-except that multi-way if-expressions do not alter the layout.
+</para>
+
+<para>Multi-way if expressions introduce a new layout context. So the
+example above is equivalent to:
+<programlisting>
+ if { | guard1 -> expr1
+ ; | ...
+ ; | guardN -> exprN
+ }
+</programlisting>
+The following behaves as expected:
+<programlisting>
+ if | guard1 -> if | guard2 -> expr2
+ | guard3 -> expr3
+ | guard4 -> expr4
+</programlisting>
+because layout translates it as
+<programlisting>
+ if { | guard1 -> if { | guard2 -> expr2
+ ; | guard3 -> expr3
+ }
+ ; | guard4 -> expr4
+ }
+</programlisting>
+Layout with multi-way if works in the same way as other layout
+contexts, except that the semi-colons between guards in a multi-way if
+are optional. So it is not necessary to line up all the guards at the
+same column; this is consistent with the way guards work in function
+definitions and case expressions.
</para>
</sect2>
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