[svn:perl6-synopsis] r13543 - doc/trunk/design/syn
Author: larry
Date: Mon Jan 29 10:39:25 2007
New Revision: 13543
Modified:
doc/trunk/design/syn/S04.pod
Log:
Note that take is intended to work en passant as suggested by gabriele renzi++
Also clarified that gather provides a void context to its victim.
Modified: doc/trunk/design/syn/S04.pod
==
--- doc/trunk/design/syn/S04.pod(original)
+++ doc/trunk/design/syn/S04.podMon Jan 29 10:39:25 2007
@@ -12,9 +12,9 @@
Maintainer: Larry Wall [EMAIL PROTECTED]
Date: 19 Aug 2004
- Last Modified: 25 Jan 2007
+ Last Modified: 29 Jan 2007
Number: 4
- Version: 48
+ Version: 49
This document summarizes Apocalypse 4, which covers the block and
statement syntax of Perl.
@@ -435,13 +435,33 @@
explicit because it's not out front where it can be seen. You can, of
course, use a placeholder parameter if you also use Creturn.)
+=head2 The gather statement
+
A variant of Cdo is Cgather. Like Cdo, it is followed by a
-statement or block, and executes it once. Unlike Cdo, its return
-value is specified by calling the Ctake function one or more times
-within the dynamic scope of the gather. The returned values are in
-the form of a lazy multislice, with each dimension corresponding to
-one Ctake slice. (A multislice is flattened in most list contexts.).
-A Cgather is not considered a loop.
+statement or block, and executes it once. Unlike Cdo, it evaluates the
+statement or block in void context; its return
+value is instead specified by calling the Ctake function one or more times
+within the dynamic scope of the gather. The returned values are in the
+form of a lazy multislice, with each slice corresponding to one
+Ctake capture. (A multislice is lazily flattened in normal list context,
+but you may unflatten it again with a @@() contextualizer.)
+
+Because Cgather evaluates its block or statement in void context,
+this typically causes the Ctake statement to be evaluated in void
+context. However, a Ctake statement that is not in void context
+gathers its arguments Ien passant and also returns them unchanged.
+This makes it easy to keep track of what you last took:
+
+my @uniq = gather for @list {
+state $previous = take $_;
+next if $_ === $previous;
+$previous = take $_;
+}
+
+A Cgather is not considered a loop, but it is easy to combine with a loop
+as in the example above.
+
+=head2 Other Cdo-like forms
Other similar CCode-only forms may also take bare statements,
including Ctry, Ccontend, Casync, and Clazy. These constructs
Re: [svn:perl6-synopsis] r13543 - doc/trunk/design/syn
On Mon, Jan 29, 2007 at 10:39:27AM -0800, [EMAIL PROTECTED] wrote:
+Because Cgather evaluates its block or statement in void context,
+this typically causes the Ctake statement to be evaluated in void
+context. However, a Ctake statement that is not in void context
+gathers its arguments Ien passant and also returns them unchanged.
+This makes it easy to keep track of what you last took:
+
+my @uniq = gather for @list {
+state $previous = take $_;
+next if $_ === $previous;
+$previous = take $_;
+}
What does it mean for take to be evaluated in void context?
What are the gathered values here?
take 1, 2; # easy. flattened 1 and then 2, right?
@x = take 1, 2; # same thing?
$x = take 1, 2; # same thing? [1, 2]?
--
Gaal Yahas [EMAIL PROTECTED]
http://gaal.livejournal.com/
Re: [svn:perl6-synopsis] r13543 - doc/trunk/design/syn
On Mon, Jan 29, 2007 at 10:01:08PM +0200, Gaal Yahas wrote:
+Because Cgather evaluates its block or statement in void context,
+this typically causes the Ctake statement to be evaluated in void
+context. However, a Ctake statement that is not in void context
+gathers its arguments Ien passant and also returns them unchanged.
+This makes it easy to keep track of what you last took:
+
+my @uniq = gather for @list {
+state $previous = take $_;
+next if $_ === $previous;
+$previous = take $_;
+}
What does it mean for take to be evaluated in void context?
What are the gathered values here?
take 1, 2; # easy. flattened 1 and then 2, right?
@x = take 1, 2; # same thing?
$x = take 1, 2; # same thing? [1, 2]?
In fact, $x = take 5;# if this were Perl 5, I might expect
# either 1 or [1] here!
--
Gaal Yahas [EMAIL PROTECTED]
http://gaal.livejournal.com/
Re: [svn:perl6-synopsis] r13543 - doc/trunk/design/syn
On Mon, Jan 29, 2007 at 10:08:34PM +0200, Gaal Yahas wrote:
On Mon, Jan 29, 2007 at 10:01:08PM +0200, Gaal Yahas wrote:
+Because Cgather evaluates its block or statement in void context,
+this typically causes the Ctake statement to be evaluated in void
+context. However, a Ctake statement that is not in void context
+gathers its arguments Ien passant and also returns them unchanged.
+This makes it easy to keep track of what you last took:
+
+my @uniq = gather for @list {
+state $previous = take $_;
+next if $_ === $previous;
+$previous = take $_;
+}
What does it mean for take to be evaluated in void context?
What are the gathered values here?
take 1, 2; # easy. flattened 1 and then 2, right?
@x = take 1, 2; # same thing?
$x = take 1, 2; # same thing? [1, 2]?
In fact, $x = take 5;# if this were Perl 5, I might expect
# either 1 or [1] here!
Ugh, sorry, I meant either 1 or [5].
--
Gaal Yahas [EMAIL PROTECTED]
http://gaal.livejournal.com/
