Author: lwall
Date: 2010-07-08 23:04:28 +0200 (Thu, 08 Jul 2010)
New Revision: 31583
Modified:
docs/Perl6/Spec/S06-routines.pod
Log:
[S06] define a * statement to represent a call from a proto to its multis
Modified: docs/Perl6/Spec/S06-routines.pod
===================================================================
--- docs/Perl6/Spec/S06-routines.pod 2010-07-08 21:02:00 UTC (rev 31582)
+++ docs/Perl6/Spec/S06-routines.pod 2010-07-08 21:04:28 UTC (rev 31583)
@@ -16,8 +16,8 @@
Created: 21 Mar 2003
- Last Modified: 18 Jun 2010
- Version: 135
+ Last Modified: 8 Jul 2010
+ Version: 136
This document summarizes Apocalypse 6, which covers subroutines and the
new type system.
@@ -99,11 +99,24 @@
and dispatches them according to the rules of multiple dispatch as defined
for each of the various dispatchers.
-This default behavior is implied by an empty body on the proto. It may
-be overridden with an explicit proto body. The default dispatcher may be
-called from within the body using 'nextsame'. (That is, an empty body C<{}>
-is equivalent to C<{nextsame;}>.)
+This default behavior is implied by a statement consisting of a single
+C<*> (that is, a "whatever"). Hence the typical proto will simply
+have a body of C<{*}>.
+ proto method bar {*}
+
+(We don't use C<...> for that because it would fail at run time,
+and proto blocks are not stubs, but are intended to be executed.)
+
+Other statements may be inserted before and after the C<*>
+statement to capture control before or after the multi dispatch:
+
+ proto foo ($a,$b) { say "Called with $a $b"; *; say "Returning"; }
+
+(That proto is only good for multis with side effects and no return
+value, since it returns the result of C<say>, which might not be what
+you want. See below for how to fix that.)
+
The syntactic form C<&foo> (without a modifying signature) can never refer to
a multi candidate. It may only refer to the single C<only> or C<proto> routine
that would first be called by C<foo()>. Individual multis may be named by
@@ -135,10 +148,29 @@
my proto sub foo () {
do-something-before();
- callsame; # call into the managed set, then come back
+ my |$cap = (*); # call into the managed set, then come back
do-something-after();
+ return |$cap;
}
+or more simply:
+
+ my proto sub foo () {
+ ENTER do-something-before();
+ *;
+ LEAVE do-something-after();
+ }
+
+Note that in the first example the C<*> must be placed into a
+context where it is a standalone statement in order to get its
+return value.
+
+Another common variant would be to propagate control to the
+outer/higher routine that would have been found if this one didn't
+exist:
+
+ my proto method foo { *; UNDO nextsame; } # failover to super foo
+
Note that, in addition to making multis work similarly to each other,
the new proto semantics greatly simplify top-level dispatchers, which
never have to worry about multis, because multis are always in the
