CPS
view release on metacpan or search on metacpan
use strict;
use warnings;
use Module::Build;
my $build = Module::Build->new(
module_name => 'CPS',
recommends => {
'Sub::Name' => 0,
},
configure_requires => {
'Module::Build' => '0.4004', # test_requires
},
test_requires => {
'Test::Identity' => 0,
'Test::Fatal' => 0,
'Test::More' => 0,
'Test::Refcount' => 0,
},
requires => {
'Future' => 0,
},
license => 'perl',
create_license => 1,
create_readme => 1,
);
$build->create_build_script;
Revision history for CPS
0.19 2019-05-20 11:31:46
[CHANGES]
* Removed CPS::Future and unit test for it
* Added deprecation warning and SEE ALSO links to Future and
Future::AsyncAwait
* Build script updates and unit test style fixes
0.18 CHANGES:
* Moved CPS::Future out to its own distribution, Future. Retained a
small back-compat wrapper for now
* Implement gkpar in terms of gkforeach so it respects the governor's
->enter method
0.17 CHANGES:
* Supply ->done_cb, ->fail_cb, ->cancel_cb callback-generation
methods to CPS::Future
* Allow future chaining for cancellation
0.16 CHANGES:
* Allow passing CPS::Future objects into others for on_ready, on_done
and on_fail callbacks (RT78432)
* Override calling on a CPS::Future to invoke ->done directly
0.15 CHANGES:
* More work on CPS::Future - added ->and_then, ->transform
0.14 CHANGES:
* Handle Carp 1.25's new message format - RT 75377
0.13 CHANGES:
* More work on CPS::Future - added cancellation, on_fail/on_done,
needs_all constructor
* Also build_requires Test::Fatal
0.12 CHANGES:
* Some initial work on CPS::Future
0.11 CHANGES:
* Added kpareach()
* Renamed kloop() to kwhile(); added transparent back-compatibility
redirect
0.10 CHANGES:
* Moved data-flow functional functions into their own CPS::Functional
namespace
* Don't check ref($k) eq "CODE" - may get in the way of Clever Tricks
(e.g. callable objects)
BUGFIXES:
* Scrub @_ in continuation from kwhile() and kpar() - fixes RT 55787
* Implement gkwhile() using a fixpoint combinator to avoid weakref
bugs on perl 5.6 entirely
0.09 CHANGES:
* Added kseq()
* Minor documentation updates
* Skip t/32leakcheck.t before perl version 5.8.0
0.08 CHANGES:
* Added kpar()
* Only opportunisticly use Sub::Name, don't hard-depend on it in case
of pure-perl scenarios
0.07 CHANGES:
* Added note about perl before 5.8 not implementing weaken properly,
so possible memory leaks if gkwhile()'s continuations are lost
BUGFIXES:
* Second attempt at making gkwhile() work on perl 5.6
0.06 CHANGES:
* Created CPS::Governor::Deferred
* Use Sub::Name to correctly name the gkwhile iteration closure
0.05 CHANGES:
* Added kdescendd() and kdescendb()
* (Hopefully) work on perl 5.6 again
* Created the concept of a Governor and implemented a simple one
0.04 CHANGES:
* Added dropk() analogous to liftk()
* Added 'use warnings'
* Various small updates to keep CPANTS happy
0.03 BUGFIXES:
* Declare dependency on at least perl 5.8 since weaken() fails tests on
earlier perls
0.02 CHANGES:
* Use Scalar::Util::weaken() in kwhile(), breaking cycle for $iter
and allowing body to care less about leaks. Also allows passthrough
of $k without intermediate sub{}
0.01 First version, released on an unsuspecting world.
This software is copyright (c) 2019 by Paul Evans <leonerd@leonerd.org.uk>.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
Terms of the Perl programming language system itself
a) the GNU General Public License as published by the Free
Software Foundation; either version 1, or (at your option) any
later version, or
b) the "Artistic License"
--- The GNU General Public License, Version 1, February 1989 ---
This software is Copyright (c) 2019 by Paul Evans <leonerd@leonerd.org.uk>.
This is free software, licensed under:
The GNU General Public License, Version 1, February 1989
GNU GENERAL PUBLIC LICENSE
Version 1, February 1989
Copyright (C) 1989 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
Preamble
The license agreements of most software companies try to keep users
at the mercy of those companies. By contrast, our General Public
License is intended to guarantee your freedom to share and change free
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General Public License applies to the Free Software Foundation's
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When we speak of free software, we are referring to freedom, not
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To protect your rights, we need to make restrictions that forbid
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We protect your rights with two steps: (1) copyright the software, and
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The precise terms and conditions for copying, distribution and
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GNU GENERAL PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License Agreement applies to any program or other work which
contains a notice placed by the copyright holder saying it may be
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Appendix: How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest
possible use to humanity, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
To do so, attach the following notices to the program. It is safest to
attach them to the start of each source file to most effectively convey
the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.
<one line to give the program's name and a brief idea of what it does.>
Copyright (C) 19yy <name of author>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
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This program is distributed in the hope that it will be useful,
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Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this
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Gnomovision version 69, Copyright (C) 19xx name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the
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c'; they could even be mouse-clicks or menu items--whatever suits your
program.
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. Here a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the
program `Gnomovision' (a program to direct compilers to make passes
at assemblers) written by James Hacker.
<signature of Ty Coon>, 1 April 1989
Ty Coon, President of Vice
That's all there is to it!
--- The Artistic License 1.0 ---
This software is Copyright (c) 2019 by Paul Evans <leonerd@leonerd.org.uk>.
This is free software, licensed under:
The Artistic License 1.0
The Artistic License
Preamble
The intent of this document is to state the conditions under which a Package
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WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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The End
Build.PL
Changes
examples/kforeach.pl
lib/CPS.pm
lib/CPS/Functional.pm
lib/CPS/Governor.pm
lib/CPS/Governor/Deferred.pm
lib/CPS/Governor/Simple.pm
LICENSE
MANIFEST This list of files
META.json
META.yml
README
t/00use.t
t/01kloop.t
t/02kforeach.t
t/03kdescend.t
t/04kpar.t
t/05kpareach.t
t/06kseq.t
t/10liftk.t
t/11dropk.t
t/20governor-simple.t
t/21governor-deferred.t
t/30governor.t
t/31caller.t
t/32leakcheck.t
t/40kmap.t
t/41kgrep.t
t/42kfold.t
t/43kunfold.t
t/99pod.t
{
"abstract" : "manage flow of control in Continuation-Passing Style",
"author" : [
"Paul Evans <leonerd@leonerd.org.uk>"
],
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"license" : [
"perl_5"
],
"meta-spec" : {
"url" : "http://search.cpan.org/perldoc?CPAN::Meta::Spec",
"version" : 2
},
"name" : "CPS",
"prereqs" : {
"configure" : {
"requires" : {
"Module::Build" : "0.4004"
}
},
"runtime" : {
"recommends" : {
"Sub::Name" : "0"
},
"requires" : {
"Future" : "0"
}
},
"test" : {
"requires" : {
"Test::Fatal" : "0",
"Test::Identity" : "0",
"Test::More" : "0",
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}
},
"provides" : {
"CPS" : {
"file" : "lib/CPS.pm",
"version" : "0.19"
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"version" : "0.19"
},
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"file" : "lib/CPS/Governor/Simple.pm",
"version" : "0.19"
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},
"release_status" : "stable",
"resources" : {
"license" : [
"http://dev.perl.org/licenses/"
]
},
"version" : "0.19",
"x_serialization_backend" : "JSON::PP version 4.00"
}
---
abstract: 'manage flow of control in Continuation-Passing Style'
author:
- 'Paul Evans <leonerd@leonerd.org.uk>'
build_requires:
Test::Fatal: '0'
Test::Identity: '0'
Test::More: '0'
Test::Refcount: '0'
configure_requires:
Module::Build: '0.4004'
dynamic_config: 1
generated_by: 'Module::Build version 0.4224, CPAN::Meta::Converter version 2.150010'
license: perl
meta-spec:
url: http://module-build.sourceforge.net/META-spec-v1.4.html
version: '1.4'
name: CPS
provides:
CPS:
file: lib/CPS.pm
version: '0.19'
CPS::Functional:
file: lib/CPS/Functional.pm
version: '0.19'
CPS::Governor:
file: lib/CPS/Governor.pm
version: '0.19'
CPS::Governor::Deferred:
file: lib/CPS/Governor/Deferred.pm
version: '0.19'
CPS::Governor::Simple:
file: lib/CPS/Governor/Simple.pm
version: '0.19'
recommends:
Sub::Name: '0'
requires:
Future: '0'
resources:
license: http://dev.perl.org/licenses/
version: '0.19'
x_serialization_backend: 'CPAN::Meta::YAML version 0.018'
NAME
CPS - manage flow of control in Continuation-Passing Style
OVERVIEW
Note: This module is entirely deprecated now. It is maintained for
compatibility for any code still using it, but please consider
rewriting to use Future instead, which offers a far neater method of
representing asynchronous program and data flow. In addition,
Future::AsyncAwait can further improve readability of Future-based
code by letting it use the familiar kinds of Perl control structure
while still being asynchronous.
At some later date this entire CPS module distribution may be
deleted.
The functions in this module implement or assist the writing of
programs, or parts of them, in Continuation Passing Style (CPS).
Briefly, CPS is a style of writing code where the normal call/return
mechanism is replaced by explicit "continuations", values passed in to
functions which they should invoke, to implement return behaviour. For
more detail on CPS, see the SEE ALSO section.
What this module implements is not in fact true CPS, as Perl does not
natively support the idea of a real continuation (such as is created by
a co-routine). Furthermore, for CPS to be efficient in languages that
natively support it, their runtimes typically implement a lot of
optimisation of CPS code, which the Perl interpreter would be unable to
perform. Instead, CODE references are passed around to stand in their
place. While not particularly useful for most regular cases, this
becomes very useful whenever some form of asynchronous or event-based
programming is being used. Continuations passed in to the body function
of a control structure can be stored in the event handlers of the
asynchronous or event-driven framework, so that when they are invoked
later, the code continues, eventually arriving at its final answer at
some point in the future.
In order for these examples to make sense, a fictional and simple
asynchronisation framework has been invented. The exact details of
operation should not be important, as it simply stands to illustrate
the point. I hope its general intention should be obvious. :)
read_stdin_line( \&on_line ); # wait on a line from STDIN, then pass it
# to the handler function
This module itself provides functions that manage the flow of control
through a continuation passing program. They do not directly facilitate
the flow of data through a program. That can be managed by lexical
variables captured by the closures passed around. See the EXAMPLES
section.
For CPS versions of data-flow functionals, such as map and grep, see
also CPS::Functional.
SYNOPSIS
use CPS qw( kloop );
kloop( sub {
my ( $knext, $klast ) = @_;
print "Enter a number, or q to quit: ";
read_stdin_line( sub {
my ( $first ) = @_;
chomp $first;
return $klast->() if $first eq "q";
print "Enter a second number: ";
read_stdin_line( sub {
my ( $second ) = @_;
print "The sum is " . ( $first + $second ) . "\n";
$knext->();
} );
} );
},
sub { exit }
);
FUNCTIONS
In all of the following functions, the \&body function can provide
results by invoking its continuation / one of its continuations, either
synchronously or asynchronously at some point later (via some event
handling or other mechanism); the next invocation of \&body will not
take place until the previous one exits if it is done synchronously.
They all take the prefix k before the name of the regular perl keyword
or function they aim to replace. It is common in CPS code in other
languages, such as Scheme or Haskell, to store a continuation in a
variable called k. This convention is followed here.
kloop( \&body, $k )
CPS version of perl's while(true) loop. Repeatedly calls the body code
until it indicates the end of the loop, then invoke $k.
$body->( $knext, $klast )
$knext->()
$klast->()
$k->()
If $knext is invoked, the body will be called again. If $klast is
invoked, the continuation $k is invoked.
kwhile( \&body, $k )
Compatibility synonym for kloop; it was renamed after version 0.10. New
code should use kloop instead.
kforeach( \@items, \&body, $k )
CPS version of perl's foreach loop. Calls the body code once for each
element in @items, until either the items are exhausted or the body
invokes its $klast continuation, then invoke $k.
$body->( $item, $knext, $klast )
$knext->()
$klast->()
$k->()
kdescendd( $root, \&body, $k )
CPS version of recursive descent on a tree-like structure, defined by a
function, body, which when given a node in the tree, yields a list of
child nodes.
$body->( $node, $kmore )
$kmore->( @child_nodes )
$k->()
The first value to be passed into body is $root.
At each iteration, a node is given to the body function, and it is
expected to pass a list of child nodes into its $kmore continuation.
These will then be iterated over, in the order given. The tree-like
structure is visited depth-first, descending fully into one subtree of
a node before moving on to the next.
This function does not provide a way for the body to accumulate a
resultant data structure to pass into its own continuation. The body is
executed simply for its side-effects and its continuation is invoked
with no arguments. A variable of some sort should be shared between the
body and the continuation if this is required.
kdescendb( $root, \&body, $k )
A breadth-first variation of kdescendd. This function visits each child
node of the parent, before iterating over all of these nodes's
children, recursively until the bottom of the tree.
kpar( @bodies, $k )
This CPS function takes a list of function bodies and calls them all
immediately. Each is given its own continuation. Once every body has
invoked its continuation, the main continuation $k is invoked.
$body->( $kdone )
$kdone->()
$k->()
This allows running multiple operations in parallel, and waiting for
them all to complete before continuing. It provides in a CPS form
functionality similar to that provided in a more object-oriented
fashion by modules such as Async::MergePoint or Event::Join.
kpareach( \@items, \&body, $k )
This CPS function takes a list of items and a function body, and calls
the body immediately once for each item in the list. Each invocation is
given its own continuation. Once every body has invoked its
continuation, the main continuation $k is invoked.
$body->( $item, $kdone )
$kdone->()
$k->()
This is similar to kforeach, except that the body is started
concurrently for all items in the list list, rather than each item
waiting for the previous to finish.
kseq( @bodies, $k )
This CPS function takes a list of function bodies and calls them each,
one at a time in sequence. Each is given a continuation to invoke,
which will cause the next body to be invoked. When the last body has
invoked its continuation, the main continuation $k is invoked.
$body->( $kdone )
$kdone->()
$k->()
A benefit of this is that it allows a long operation that uses many
continuation "pauses", to be written without code indenting further and
further to the right. Another is that it allows easy skipping of
conditional parts of a computation, which would otherwise be tricky to
write in a CPS form. See the EXAMPLES section.
GOVERNORS
All of the above functions are implemented using a loop which
repeatedly calls the body function until some terminating condition. By
controlling the way this loop re-invokes itself, a program can control
the behaviour of the functions.
For every one of the above functions, there also exists a variant which
takes a CPS::Governor object as its first argument. These functions use
the governor object to control their iteration.
kloop( \&body, $k )
gkloop( $gov, \&body, $k )
kforeach( \@items, \&body, $k )
gkforeach( $gov, \@items, \&body, $k )
etc...
In this way, other governor objects can be constructed which have
different running properties; such as interleaving iterations of their
loop with other IO activity in an event-driven framework, or giving
rate-limitation control on the speed of iteration of the loop.
CPS UTILITIES
These function names do not begin with k because they are not
themselves CPS primatives, but may be useful in CPS-oriented code.
$kfunc = liftk { BLOCK }
$kfunc = liftk( \&func )
Returns a new CODE reference to a CPS-wrapped version of the code block
or passed CODE reference. When $kfunc is invoked, the function &func is
called in list context, being passed all the arguments given to $kfunc
apart from the last, expected to be its continuation. When &func
returns, the result is passed into the continuation.
$kfunc->( @func_args, $k )
$k->( @func_ret )
The following are equivalent
print func( 1, 2, 3 );
my $kfunc = liftk( \&func );
$kfunc->( 1, 2, 3, sub { print @_ } );
Note that the returned wrapper function only has one continuation slot
in its arguments. It therefore cannot be used as the body for kloop(),
kforeach() or kgenerate(), because these pass two continuations. There
does not exist a "natural" way to lift a normal call/return function
into a CPS function which requires more than one continuation, because
there is no way to distinguish the different named returns.
$func = dropk { BLOCK } $kfunc
$func = dropk $waitfunc, $kfunc
Returns a new CODE reference to a plain call/return version of the
passed CPS-style CODE reference. When the returned ("dropped") function
is called, it invokes the passed CPS function, then waits for it to
invoke its continuation. When it does, the list that was passed to the
continuation is returned by the dropped function. If called in scalar
context, only the first value in the list is returned.
$kfunc->( @func_args, $k )
$k->( @func_ret )
$waitfunc->()
@func_ret = $func->( @func_args )
Given the following trivial CPS function:
$kadd = sub { $_[2]->( $_[0] + $_[1] ) };
The following are equivalent
$kadd->( 10, 20, sub { print "The total is $_[0]\n" } );
$add = dropk { } $kadd;
print "The total is ".$add->( 10, 20 )."\n";
In the general case the CPS function hasn't yet invoked its
continuation by the time it returns (such as would be the case when
using any sort of asynchronisation or event-driven framework). For
dropk to actually work in this situation, it requires a way to run the
event framework, to cause it to process events until the continuation
has been invoked.
This is provided by the block, or the first passed CODE reference. When
the returned function is invoked, it repeatedly calls the block or wait
function, until the CPS function has invoked its continuation.
EXAMPLES
Returning Data From Functions
No facilities are provided directly to return data from CPS body
functions in kloop, kpar and kseq. Instead, normal lexical variable
capture may be used here.
my $bat;
my $ball;
kpar(
sub {
my ( $k ) = @_;
get_bat( on_bat => sub { $bat = shift; goto &$k } );
},
sub {
my ( $k ) = @_;
serve_ball( on_ball => sub { $ball = shift; goto &$k } );
},
sub {
$bat->hit( $ball );
},
);
The body function can set the value of a variable that it and its final
continuation both capture.
Using kseq For Conditionals
Consider the call/return style of code
A();
if( $maybe ) {
B();
}
C();
We cannot easily write this in CPS form without naming C twice
kA( sub {
$maybe ?
kB( sub { kC() } ) :
kC();
} );
While not so problematic here, it could get awkward if C were in fact a
large code block, or if more than a single conditional were employed in
the logic; a likely scenario. A further issue is that the logical
structure becomes much harder to read.
Using kseq allows us to name the continuation so each arm of kmaybe can
invoke it indirectly.
kseq(
\&kA,
sub { my $k = shift; $maybe ? kB( $k ) : goto &$k; },
\&kC
);
SEE ALSO
* Future - represent an operation awaiting completion
* Future::AsyncAwait - deferred subroutine syntax for futures
* CPS::Functional - functional utilities in Continuation-Passing
Style
* http://en.wikipedia.org/wiki/Continuation-passing_style on
wikipedia
ACKNOWLEDGEMENTS
Matt S. Trout (mst) <mst@shadowcat.co.uk> - for the inspiration of
kpareach and with apologies to for naming of the said. ;)
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
examples/kforeach.pl view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use CPS qw( gkforeach kpar );
use CPS::Governor::Deferred;
my $gov = CPS::Governor::Deferred->new;
gkforeach( $gov, [ 1 .. 10 ],
sub {
my ( $item, $knext ) = @_;
print "A$item ";
goto &$knext;
},
sub {},
);
gkforeach( $gov, [ 1 .. 10 ],
sub {
my ( $item, $knext ) = @_;
print "B$item ";
goto &$knext;
},
sub {},
);
$gov->flush;
print "\n";
# You may distribute under the terms of either the GNU General Public License
# or the Artistic License (the same terms as Perl itself)
#
# (C) Paul Evans, 2008-2010 -- leonerd@leonerd.org.uk
package CPS;
use strict;
use warnings;
our $VERSION = '0.19';
use Carp;
our @CPS_PRIMS = qw(
kloop
kwhile
kforeach
kdescendd kdescendb
kpar
kpareach
kseq
);
our @EXPORT_OK = (
@CPS_PRIMS,
map( "g$_", @CPS_PRIMS ),
qw(
liftk
dropk
),
);
use Exporter 'import';
use CPS::Governor::Simple;
# Don't hard-depend on Sub::Name since it's only a niceness for stack traces
BEGIN {
if( eval { require Sub::Name } ) {
*subname = \&Sub::Name::subname;
}
else {
# Ignore the name, return the CODEref
*subname = sub { return $_[1] };
}
}
=head1 NAME
C<CPS> - manage flow of control in Continuation-Passing Style
=head1 OVERVIEW
=over 4
B<Note>: This module is entirely deprecated now. It is maintained for
compatibility for any code still using it, but please consider rewriting to
use L<Future> instead, which offers a far neater method of representing
asynchronous program and data flow. In addition, L<Future::AsyncAwait> can
further improve readability of C<Future>-based code by letting it use the
familiar kinds of Perl control structure while still being asynchronous.
At some later date this entire C<CPS> module distribution may be deleted.
=back
The functions in this module implement or assist the writing of programs, or
parts of them, in Continuation Passing Style (CPS). Briefly, CPS is a style
of writing code where the normal call/return mechanism is replaced by explicit
"continuations", values passed in to functions which they should invoke, to
implement return behaviour. For more detail on CPS, see the SEE ALSO section.
What this module implements is not in fact true CPS, as Perl does not natively
support the idea of a real continuation (such as is created by a co-routine).
Furthermore, for CPS to be efficient in languages that natively support it,
their runtimes typically implement a lot of optimisation of CPS code, which
the Perl interpreter would be unable to perform. Instead, CODE references are
passed around to stand in their place. While not particularly useful for most
regular cases, this becomes very useful whenever some form of asynchronous or
event-based programming is being used. Continuations passed in to the body
function of a control structure can be stored in the event handlers of the
asynchronous or event-driven framework, so that when they are invoked later,
the code continues, eventually arriving at its final answer at some point in
the future.
In order for these examples to make sense, a fictional and simple
asynchronisation framework has been invented. The exact details of operation
should not be important, as it simply stands to illustrate the point. I hope
its general intention should be obvious. :)
read_stdin_line( \&on_line ); # wait on a line from STDIN, then pass it
# to the handler function
This module itself provides functions that manage the flow of control through
a continuation passing program. They do not directly facilitate the flow of
data through a program. That can be managed by lexical variables captured by
the closures passed around. See the EXAMPLES section.
For CPS versions of data-flow functionals, such as C<map> and C<grep>, see
also L<CPS::Functional>.
=head1 SYNOPSIS
use CPS qw( kloop );
kloop( sub {
my ( $knext, $klast ) = @_;
print "Enter a number, or q to quit: ";
read_stdin_line( sub {
my ( $first ) = @_;
chomp $first;
return $klast->() if $first eq "q";
print "Enter a second number: ";
read_stdin_line( sub {
my ( $second ) = @_;
print "The sum is " . ( $first + $second ) . "\n";
$knext->();
} );
} );
},
sub { exit }
);
=cut
=head1 FUNCTIONS
In all of the following functions, the C<\&body> function can provide results
by invoking its continuation / one of its continuations, either synchronously
or asynchronously at some point later (via some event handling or other
mechanism); the next invocation of C<\&body> will not take place until the
previous one exits if it is done synchronously.
They all take the prefix C<k> before the name of the regular perl keyword or
function they aim to replace. It is common in CPS code in other languages,
such as Scheme or Haskell, to store a continuation in a variable called C<k>.
This convention is followed here.
=cut
=head2 kloop( \&body, $k )
CPS version of perl's C<while(true)> loop. Repeatedly calls the C<body> code
until it indicates the end of the loop, then invoke C<$k>.
$body->( $knext, $klast )
$knext->()
$klast->()
$k->()
If C<$knext> is invoked, the body will be called again. If C<$klast> is
invoked, the continuation C<$k> is invoked.
=head2 kwhile( \&body, $k )
Compatibility synonym for C<kloop>; it was renamed after version 0.10. New
code should use C<kloop> instead.
=cut
sub _fix
{
my ( $func ) = @_;
sub {
unshift @_, _fix( $func );
goto &$func;
};
}
sub gkloop
{
my ( $gov, $body, $k ) = @_;
# We can't just call this as a method because we need to tailcall it
# Instead, keep a reference to the actual method so we can goto &$enter
my $enter = $gov->can('enter') or croak "Governor cannot ->enter";
my $kfirst = _fix subname gkloop => sub {
my $knext = shift;
my $sync = 1;
my $do_again;
$enter->( $gov, $body,
sub {
if( $sync ) { $do_again=1 }
else { goto &$knext; }
},
sub { @_ = (); goto &$k },
);
$sync = 0;
if( $do_again ) {
$do_again = 0;
goto &$knext;
}
};
goto &$kfirst;
}
*gkwhile = \&gkloop;
=head2 kforeach( \@items, \&body, $k )
CPS version of perl's C<foreach> loop. Calls the C<body> code once for each
element in C<@items>, until either the items are exhausted or the C<body>
invokes its C<$klast> continuation, then invoke C<$k>.
$body->( $item, $knext, $klast )
$knext->()
$klast->()
$k->()
=cut
sub gkforeach
{
my ( $gov, $items, $body, $k ) = @_;
my $idx = 0;
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
goto &$klast unless $idx < scalar @$items;
@_ =(
$items->[$idx++],
$knext,
$klast
);
goto &$body;
},
$k,
);
}
=head2 kdescendd( $root, \&body, $k )
CPS version of recursive descent on a tree-like structure, defined by a
function, C<body>, which when given a node in the tree, yields a list of
child nodes.
$body->( $node, $kmore )
$kmore->( @child_nodes )
$k->()
The first value to be passed into C<body> is C<$root>.
At each iteration, a node is given to the C<body> function, and it is expected
to pass a list of child nodes into its C<$kmore> continuation. These will then
be iterated over, in the order given. The tree-like structure is visited
depth-first, descending fully into one subtree of a node before moving on to
the next.
This function does not provide a way for the body to accumulate a resultant
data structure to pass into its own continuation. The body is executed simply
for its side-effects and its continuation is invoked with no arguments. A
variable of some sort should be shared between the body and the continuation
if this is required.
=cut
sub gkdescendd
{
my ( $gov, $root, $body, $k ) = @_;
my @stack = ( $root );
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
@_ = (
shift @stack,
sub {
unshift @stack, @_;
goto &$knext if @stack;
goto &$klast;
},
);
goto &$body;
},
$k,
);
}
=head2 kdescendb( $root, \&body, $k )
A breadth-first variation of C<kdescendd>. This function visits each child
node of the parent, before iterating over all of these nodes's children,
recursively until the bottom of the tree.
=cut
sub gkdescendb
{
my ( $gov, $root, $body, $k ) = @_;
my @queue = ( $root );
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
@_ = (
shift @queue,
sub {
push @queue, @_;
goto &$knext if @queue;
goto &$klast;
},
);
goto &$body;
},
$k,
);
}
=head2 kpar( @bodies, $k )
This CPS function takes a list of function bodies and calls them all
immediately. Each is given its own continuation. Once every body has invoked
its continuation, the main continuation C<$k> is invoked.
$body->( $kdone )
$kdone->()
$k->()
This allows running multiple operations in parallel, and waiting for them all
to complete before continuing. It provides in a CPS form functionality
similar to that provided in a more object-oriented fashion by modules such as
L<Async::MergePoint> or L<Event::Join>.
=cut
sub gkpar
{
my ( $gov, @bodies ) = @_;
my $k = pop @bodies;
$gov->can('enter') or croak "Governor cannot ->enter";
my $sync = 1;
my @outstanding;
my $kdone = sub {
return if $sync;
$_ and return for @outstanding;
goto &$k;
};
gkforeach( $gov, [ 0 .. $#bodies ],
sub {
my ( $idx, $knext ) = @_;
$outstanding[$idx]++;
$gov->enter( $bodies[$idx], sub {
$outstanding[$idx]--;
@_ = ();
goto &$kdone;
} );
goto &$knext;
},
sub {
$sync = 0;
@_ = ();
goto &$kdone;
}
);
}
=head2 kpareach( \@items, \&body, $k )
This CPS function takes a list of items and a function body, and calls the
body immediately once for each item in the list. Each invocation is given its
own continuation. Once every body has invoked its continuation, the main
continuation C<$k> is invoked.
$body->( $item, $kdone )
$kdone->()
$k->()
This is similar to C<kforeach>, except that the body is started concurrently
for all items in the list list, rather than each item waiting for the previous
to finish.
=cut
sub gkpareach
{
my ( $gov, $items, $body, $k ) = @_;
gkpar( $gov,
(map {
my $item = $_;
sub {
unshift @_, $item;
goto &$body
}
} @$items),
$k
);
}
=head2 kseq( @bodies, $k )
This CPS function takes a list of function bodies and calls them each, one at
a time in sequence. Each is given a continuation to invoke, which will cause
the next body to be invoked. When the last body has invoked its continuation,
the main continuation C<$k> is invoked.
$body->( $kdone )
$kdone->()
$k->()
A benefit of this is that it allows a long operation that uses many
continuation "pauses", to be written without code indenting further and
further to the right. Another is that it allows easy skipping of conditional
parts of a computation, which would otherwise be tricky to write in a CPS
form. See the EXAMPLES section.
=cut
sub gkseq
{
my ( $gov, @bodies ) = @_;
my $k = pop @bodies;
my $enter = $gov->can('enter') or croak "Governor cannot ->enter";
while( @bodies ) {
my $nextk = $k;
my $b = pop @bodies;
$k = sub {
@_ = ( $gov, $b, $nextk );
goto &$enter;
};
}
@_ = ();
goto &$k;
}
=head1 GOVERNORS
All of the above functions are implemented using a loop which repeatedly calls
the body function until some terminating condition. By controlling the way
this loop re-invokes itself, a program can control the behaviour of the
functions.
For every one of the above functions, there also exists a variant which takes
a L<CPS::Governor> object as its first argument. These functions use the
governor object to control their iteration.
kloop( \&body, $k )
gkloop( $gov, \&body, $k )
kforeach( \@items, \&body, $k )
gkforeach( $gov, \@items, \&body, $k )
etc...
In this way, other governor objects can be constructed which have different
running properties; such as interleaving iterations of their loop with other
IO activity in an event-driven framework, or giving rate-limitation control on
the speed of iteration of the loop.
=cut
# The above is a lie. The basic functions provided are actually the gk*
# versions; we wrap these to make the normal k* functions by passing a simple
# governor.
sub _governate
{
my $pkg = caller;
my ( $func, $name ) = @_;
my $default_gov = CPS::Governor::Simple->new;
no strict 'refs';
my $code = $pkg->can( $func ) or croak "$pkg cannot $func()";
*{$pkg."::$name"} = subname $name => sub {
unshift @_, $default_gov;
goto &$code;
};
}
_governate "g$_" => $_ for @CPS_PRIMS;
=head1 CPS UTILITIES
These function names do not begin with C<k> because they are not themselves
CPS primatives, but may be useful in CPS-oriented code.
=cut
=head2 $kfunc = liftk { BLOCK }
=head2 $kfunc = liftk( \&func )
Returns a new CODE reference to a CPS-wrapped version of the code block or
passed CODE reference. When C<$kfunc> is invoked, the function C<&func> is
called in list context, being passed all the arguments given to C<$kfunc>
apart from the last, expected to be its continuation. When C<&func> returns,
the result is passed into the continuation.
$kfunc->( @func_args, $k )
$k->( @func_ret )
The following are equivalent
print func( 1, 2, 3 );
my $kfunc = liftk( \&func );
$kfunc->( 1, 2, 3, sub { print @_ } );
Note that the returned wrapper function only has one continuation slot in its
arguments. It therefore cannot be used as the body for C<kloop()>,
C<kforeach()> or C<kgenerate()>, because these pass two continuations. There
does not exist a "natural" way to lift a normal call/return function into a
CPS function which requires more than one continuation, because there is no
way to distinguish the different named returns.
=cut
sub liftk(&)
{
my ( $code ) = @_;
return sub {
my $k = pop;
@_ = $code->( @_ );
goto &$k;
};
}
=head2 $func = dropk { BLOCK } $kfunc
=head2 $func = dropk $waitfunc, $kfunc
Returns a new CODE reference to a plain call/return version of the passed
CPS-style CODE reference. When the returned ("dropped") function is called,
it invokes the passed CPS function, then waits for it to invoke its
continuation. When it does, the list that was passed to the continuation is
returned by the dropped function. If called in scalar context, only the first
value in the list is returned.
$kfunc->( @func_args, $k )
$k->( @func_ret )
$waitfunc->()
@func_ret = $func->( @func_args )
Given the following trivial CPS function:
$kadd = sub { $_[2]->( $_[0] + $_[1] ) };
The following are equivalent
$kadd->( 10, 20, sub { print "The total is $_[0]\n" } );
$add = dropk { } $kadd;
print "The total is ".$add->( 10, 20 )."\n";
In the general case the CPS function hasn't yet invoked its continuation by
the time it returns (such as would be the case when using any sort of
asynchronisation or event-driven framework). For C<dropk> to actually work in
this situation, it requires a way to run the event framework, to cause it to
process events until the continuation has been invoked.
This is provided by the block, or the first passed CODE reference. When the
returned function is invoked, it repeatedly calls the block or wait function,
until the CPS function has invoked its continuation.
=cut
sub dropk(&$)
{
my ( $waitfunc, $kfunc ) = @_;
return sub {
my @result;
my $done;
$kfunc->( @_, sub { @result = @_; $done = 1 } );
while( !$done ) {
$waitfunc->();
}
return wantarray ? @result : $result[0];
}
}
=head1 EXAMPLES
=head2 Returning Data From Functions
No facilities are provided directly to return data from CPS body functions in
C<kloop>, C<kpar> and C<kseq>. Instead, normal lexical variable capture may
be used here.
my $bat;
my $ball;
kpar(
sub {
my ( $k ) = @_;
get_bat( on_bat => sub { $bat = shift; goto &$k } );
},
sub {
my ( $k ) = @_;
serve_ball( on_ball => sub { $ball = shift; goto &$k } );
},
sub {
$bat->hit( $ball );
},
);
The body function can set the value of a variable that it and its final
continuation both capture.
=head2 Using C<kseq> For Conditionals
Consider the call/return style of code
A();
if( $maybe ) {
B();
}
C();
We cannot easily write this in CPS form without naming C twice
kA( sub {
$maybe ?
kB( sub { kC() } ) :
kC();
} );
While not so problematic here, it could get awkward if C were in fact a large
code block, or if more than a single conditional were employed in the logic; a
likely scenario. A further issue is that the logical structure becomes much
harder to read.
Using C<kseq> allows us to name the continuation so each arm of C<kmaybe> can
invoke it indirectly.
kseq(
\&kA,
sub { my $k = shift; $maybe ? kB( $k ) : goto &$k; },
\&kC
);
=head1 SEE ALSO
=over 4
=item *
L<Future> - represent an operation awaiting completion
=item *
L<Future::AsyncAwait> - deferred subroutine syntax for futures
=item *
L<CPS::Functional> - functional utilities in Continuation-Passing Style
=item *
L<http://en.wikipedia.org/wiki/Continuation-passing_style> on wikipedia
=back
=head1 ACKNOWLEDGEMENTS
Matt S. Trout (mst) <mst@shadowcat.co.uk> - for the inspiration of C<kpareach>
and with apologies to for naming of the said. ;)
=head1 AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
=cut
0x55AA;
lib/CPS/Functional.pm view on Meta::CPAN
# You may distribute under the terms of either the GNU General Public License
# or the Artistic License (the same terms as Perl itself)
#
# (C) Paul Evans, 2010 -- leonerd@leonerd.org.uk
package CPS::Functional;
use strict;
use warnings;
our $VERSION = '0.19';
use Carp;
use Exporter 'import';
use CPS qw( gkloop );
our @CPS_PRIMS = qw(
kmap
kgrep
kfoldl kfoldr
kunfold
);
our @EXPORT_OK = (
@CPS_PRIMS,
map( "g$_", @CPS_PRIMS ),
);
# Don't hard-depend on Sub::Name since it's only a niceness for stack traces
BEGIN {
if( eval { require Sub::Name } ) {
*subname = \&Sub::Name::subname;
}
else {
# Ignore the name, return the CODEref
*subname = sub { return $_[1] };
}
}
=head1 NAME
C<CPS::Functional> - functional utilities in Continuation-Passing Style
=head1 SYNOPSIS
use CPS::Functional qw( kmap );
use Example::HTTP::Client qw( k_get_http );
use List::Util qw( sum );
my @URLs = (
"http://www.foo.com",
"http://www.bar.com",
);
kmap( \@URLs,
sub {
my ( $item, $kret ) = @_;
k_get_http( uri => $item, on_response => sub {
my ( $response ) = @_;
$kret->( $response->content_length );
} );
},
sub {
my ( @sizes ) = @_;
say "Total length of all URLs: " . sum(@sizes);
},
);
=head1 DESCRIPTION
This module provides L<CPS> versions of data-flow functionals, such as Perl's
C<map> and C<grep>, where function bodies are invoked and expected to return
data, which the functional manages. They are built on top of the control-flow
functionals provided by the C<CPS> module itself.
=cut
=head1 FUNCTIONS
=cut
=head2 kmap( \@items, \&body, $k )
CPS version of perl's C<map> statement. Calls the C<body> code once for each
element in C<@items>, capturing the list of values the body passes into its
continuation. When the items are exhausted, C<$k> is invoked and passed a list
of all the collected values.
$body->( $item, $kret )
$kret->( @items_out )
$k->( @all_items_out )
=cut
sub gkmap
{
my ( $gov, $items, $body, $k ) = @_;
ref $items eq "ARRAY" or croak 'Expected $items as ARRAY ref';
ref $body eq "CODE" or croak 'Expected $body as CODE ref';
my @ret;
my $idx = 0;
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
goto &$klast unless $idx < scalar @$items;
@_ = (
$items->[$idx++],
sub { push @ret, @_; goto &$knext }
);
goto &$body;
},
sub { $k->( @ret ) },
);
}
=head2 kgrep( \@items, \&body, $k )
CPS version of perl's C<grep> statement. Calls the C<body> code once for each
element in C<@items>, capturing those elements where the body's continuation
was invoked with a true value. When the items are exhausted, C<$k> is invoked
and passed a list of the subset of C<@items> which were selected.
$body->( $item, $kret )
$kret->( $select )
$k->( @chosen_items )
=cut
sub gkgrep
{
my ( $gov, $items, $body, $k ) = @_;
ref $items eq "ARRAY" or croak 'Expected $items as ARRAY ref';
ref $body eq "CODE" or croak 'Expected $body as CODE ref';
my @ret;
my $idx = 0;
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
goto &$klast unless $idx < scalar @$items;
my $item = $items->[$idx++];
@_ = (
$item,
sub { push @ret, $item if $_[0]; goto &$knext }
);
goto &$body;
},
sub { $k->( @ret ) },
);
}
=head2 kfoldl( \@items, \&body, $k )
CPS version of C<List::Util::reduce>, which collapses (or "folds") a list of
values down to a single scalar, by successively accumulating values together.
If C<@items> is empty, invokes C<$k> immediately, passing in C<undef>.
If C<@items> contains a single value, invokes C<$k> immediately, passing in
just that single value.
Otherwise, initialises an accumulator variable with the first value in
C<@items>, then for each additional item, invokes the C<body> passing in the
accumulator and the next item, storing back into the accumulator the value
that C<body> passed to its continuation. When the C<@items> are exhausted, it
invokes C<$k>, passing in the final value of the accumulator.
$body->( $acc, $item, $kret )
$kret->( $new_acc )
$k->( $final_acc )
Technically, this is not a true Scheme/Haskell-style C<foldl>, as it does not
take an initial value. (It is what Haskell calls C<foldl1>.) However, if such
an initial value is required, this can be provided by
kfoldl( [ $initial, @items ], \&body, $k )
=cut
sub gkfoldl
{
my ( $gov, $items, $body, $k ) = @_;
ref $items eq "ARRAY" or croak 'Expected $items as ARRAY ref';
ref $body eq "CODE" or croak 'Expected $body as CODE ref';
$k->( undef ), return if @$items == 0;
$k->( $items->[0] ), return if @$items == 1;
my $idx = 0;
my $acc = $items->[$idx++];
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
goto &$klast unless $idx < scalar @$items;
@_ = (
$acc,
$items->[$idx++],
sub { $acc = shift; goto &$knext }
);
goto &$body;
},
sub { $k->( $acc ) },
);
}
=head2 kfoldr( \@items, \&body, $k )
A right-associative version of C<kfoldl()>. Where C<kfoldl()> starts with the
first two elements in C<@items> and works forward, C<kfoldr()> starts with the
last two and works backward.
$body->( $item, $acc, $kret )
$kret->( $new_acc )
$k->( $final_acc )
As before, an initial value can be provided by modifying the C<@items> array,
though note it has to be last this time:
kfoldr( [ @items, $initial ], \&body, $k )
=cut
sub gkfoldr
{
my ( $gov, $items, $body, $k ) = @_;
ref $items eq "ARRAY" or croak 'Expected $items as ARRAY ref';
ref $body eq "CODE" or croak 'Expected $body as CODE ref';
$k->( undef ), return if @$items == 0;
$k->( $items->[0] ), return if @$items == 1;
my $idx = scalar(@$items) - 1;
my $acc = $items->[$idx--];
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
goto &$klast if $idx < 0;
@_ = (
$items->[$idx--],
$acc,
sub { $acc = shift; goto &$knext }
);
goto &$body;
},
sub { $k->( $acc ) },
);
}
=head2 kunfold( $seed, \&body, $k )
An inverse operation to C<kfoldl()>; turns a single scalar into a list of
items. Repeatedly calls the C<body> code, capturing the values it returns,
until it indicates the end of the loop, then invoke C<$k> with the collected
values.
$body->( $seed, $kmore, $kdone )
$kmore->( $new_seed, @items )
$kdone->( @items )
$k->( @all_items )
With each iteration, the C<body> is invoked and passed the current C<$seed>
value and two continuations, C<$kmore> and C<$kdone>. If C<$kmore> is invoked,
the passed items, if any, are appended to the eventual result list. The
C<body> is then re-invoked with the new C<$seed> value. If C<$klast> is
invoked, the passed items, if any, are appended to the return list, then the
entire list is passed to C<$k>.
=cut
sub gkunfold
{
my ( $gov, $seed, $body, $k ) = @_;
ref $body eq "CODE" or croak 'Expected $body as CODE ref';
my @ret;
gkloop( $gov,
sub {
my ( $knext, $klast ) = @_;
@_ = (
$seed,
sub { $seed = shift; push @ret, @_; goto &$knext },
sub { push @ret, @_; goto &$klast },
);
goto &$body;
},
sub { $k->( @ret ) },
);
}
CPS::_governate "g$_" => $_ for @CPS_PRIMS;
=head1 EXAMPLES
The following aren't necessarily examples of code which would be found in real
programs, but instead, demonstrations of how to use the above functions as
ways of controlling program flow.
Without dragging in large amount of detail on an asynchronous or event-driven
framework, it is difficult to give a useful example of behaviour that CPS
allows that couldn't be done just as easily without. Nevertheless, I hope the
following examples will be useful to demonstrate use of the above functions,
in a way which hints at their use in a real program.
=head2 Implementing C<join()> using C<kfoldl()>
use CPS::Functional qw( kfoldl );
my @words = qw( My message here );
kfoldl(
\@words,
sub {
my ( $left, $right, $k ) = @_;
$k->( "$left $right" );
},
sub {
my ( $str ) = @_;
print "Joined up words: $str\n";
}
);
=head2 Implementing C<split()> using C<kunfold()>
The following program illustrates the way that C<kunfold()> can split a
string, in a reverse way to the way C<kfoldl()> can join it.
use CPS::Functional qw( kunfold );
my $str = "My message here";
kunfold(
$str,
sub {
my ( $s, $kmore, $kdone ) = @_;
if( $s =~ s/^(.*?) // ) {
return $kmore->( $s, $1 );
}
else {
return $kdone->( $s );
}
},
sub {
my @words = @_;
print "Words in message:\n";
print "$_\n" for @words;
}
);
=head2 Generating Prime Numbers
While the design of C<kunfold()> is symmetric to C<kfoldl()>, the seed value
doesn't have to be successively broken apart into pieces. Another valid use
for it may be storing intermediate values in computation, such as in this
example, storing a list of known primes, to help generate the next one:
use CPS::Functional qw( kunfold );
kunfold(
[ 2, 3 ],
sub {
my ( $vals, $kmore, $kdone ) = @_;
return $kdone->() if @$vals >= 50;
PRIME: for( my $n = $vals->[-1] + 2; ; $n += 2 ) {
$n % $_ == 0 and next PRIME for @$vals;
push @$vals, $n;
return $kmore->( $vals, $n );
}
},
sub {
my @primes = ( 2, 3, @_ );
print "Primes are @primes\n";
}
);
=head2 Forward-reading Program Flow
One side benefit of the CPS control-flow methods which is unassociated with
asynchronous operation, is that the flow of data reads in a more natural
left-to-right direction, instead of the right-to-left flow in functional
style. Compare
sub square { $_ * $_ }
sub add { $a + $b }
print reduce( \&add, map( square, primes(10) ) );
(because C<map> is a language builtin but C<reduce> is a function with C<(&)>
prototype, it has a different way to pass in the named functions)
with
my $ksquare = liftk { $_[0] * $_[0] };
my $kadd = liftk { $_[0] + $_[1] };
kprimes 10, sub {
kmap \@_, $ksquare, sub {
kfoldl \@_, $kadd, sub {
print $_[0];
}
}
};
This translates roughly to a functional vs imperative way to describe the
problem:
Print the sum of the squares of the first 10 primes.
Take the first 10 primes. Square them. Sum them. Print.
Admittedly the closure creation somewhat clouds the point in this small
example, but in a larger example, the real problem-solving logic would be
larger, and stand out more clearly against the background boilerplate.
=head1 SEE ALSO
=over 4
=item *
L<CPS> - manage flow of control in Continuation-Passing Style
=back
=head1 AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
=cut
0x55AA;
lib/CPS/Governor.pm view on Meta::CPAN
# You may distribute under the terms of either the GNU General Public License
# or the Artistic License (the same terms as Perl itself)
#
# (C) Paul Evans, 2009-2012 -- leonerd@leonerd.org.uk
package CPS::Governor;
use strict;
use warnings;
use Carp;
our $VERSION = '0.19';
=head1 NAME
C<CPS::Governor> - control the iteration of the C<CPS> functions
=head1 DESCRIPTION
Objects based on this abstract class are used by the C<gk*> variants of the
L<CPS> functions, to control their behavior. These objects are expected to
provide a method, C<again>, which the functions will use to re-invoke
iterations of loops, and so on. By providing a different implementation of
this method, governor objects can provide such behaviours as rate-limiting,
asynchronisation or parallelism, and integration with event-based IO
frameworks.
=cut
=head1 CONSTRUCTOR
=cut
=head2 $gov = CPS::Governor->new
Must be called on a subclass which implements the C<again> method. Returns a
new instance of a governor object in that class.
=cut
sub new
{
my $class = shift;
$class->can( "again" ) or croak "Expected to be class that can ->again";
return bless {}, $class;
}
# We're using this internally in gkpar() but not documenting it currently.
# Details are still experimental.
sub enter
{
my $self = shift;
$self->again( @_ );
}
=head1 SUBCLASS METHODS
Because this is an abstract class, instances of it can only be constructed on
a subclass which implements the following methods:
=cut
=head2 $gov->again( $code, @args )
Execute the function given in the C<CODE> reference C<$code>, passing in the
arguments C<@args>. If this is going to be executed immediately, it should
be invoked using a tail-call directly by the C<again> method, so that the
stack does not grow arbitrarily. This can be achieved by, for example:
@_ = @args;
goto &$code;
Alternatively, the L<Sub::Call::Tail> may be used to apply syntactic sugar,
allowing you to write instead:
use Sub::Call::Tail;
...
tail $code->( @args );
=cut
=head1 EXAMPLES
=head2 A Governor With A Time Delay
Consider the following subclass, which implements a C<CPS::Governor> subclass
that calls C<sleep()> between every invocation.
package Governor::Sleep
use base qw( CPS::Governor );
sub new
{
my $class = shift;
my ( $delay ) = @_;
my $self = $class->SUPER::new;
$self->{delay} = $delay;
return $self;
}
sub again
{
my $self = shift;
my $code = shift;
sleep $self->{delay};
# @args are still in @_
goto &$code;
}
=cut
=head1 SEE ALSO
=over 4
=item *
L<Sub::Call::Tail> - Tail calls for subroutines and methods
=back
=head1 AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
=cut
0x55AA;
lib/CPS/Governor/Deferred.pm view on Meta::CPAN
# You may distribute under the terms of either the GNU General Public License
# or the Artistic License (the same terms as Perl itself)
#
# (C) Paul Evans, 2009 -- leonerd@leonerd.org.uk
package CPS::Governor::Deferred;
use strict;
use warnings;
use base qw( CPS::Governor );
our $VERSION = '0.19';
=head1 NAME
C<CPS::Governor::Deferred> - iterate at some later point
=head1 SYNOPSIS
use CPS qw( gkforeach );
use CPS::Governor::Deferred;
my $gov = CPS::Governor::Deferred->new;
gkforeach( $gov, [ 1 .. 10 ],
sub {
my ( $item, $knext ) = @_;
print "A$item ";
goto &$knext;
},
sub {},
);
gkforeach( $gov, [ 1 .. 10 ],
sub {
my ( $item, $knext ) = @_;
print "B$item ";
goto &$knext;
},
sub {},
);
$gov->flush;
=head1 DESCRIPTION
This L<CPS::Governor> allows the functions using it to delay their iteration
until some later point when the containing program invokes it. This allows two
main advantages:
=over 4
=item *
CPU-intensive operations may be split apart and mixed with other IO operations
=item *
Multiple control functions may be executed in pseudo-parallel, interleaving
iterations of each giving a kind of concurrency
=back
These are achieved by having the governor store a list of code references that
need to be invoked, rather than invoking them immediately. These references
can then be invoked later, perhaps by using an idle watcher in an event
framework.
Because each code reference hasn't yet been invoked by the time the C<again>
method is called, the original caller is free to store more pending references
with the governor. This allows multiple control functions to be interleaved,
as in the C<A> and C<B> example above.
=cut
=head1 CONSTRUCTOR
=cut
=head2 $gov = CPS::Governor::Deferred->new( %args )
Returns a new instance of a C<CPS::Governor::Deferred> object. Requires no
parameters but may take any of the following to adjust its default behaviour:
=over 8
=item defer_after => INT
If given some positive number, C<$n> then the first C<$n-1> invocations of the
C<again> method will in fact be executed immediately. Thereafter they will be
enqueued in the normal mechanism. This gives the effect that longrunning loops
will be executed in batches of C<$n>.
If not supplied then every invocation of C<again> will use the queueing
mechanism.
=back
=cut
sub new
{
my $class = shift;
my %args = @_;
my $self = $class->SUPER::new( %args );
$self->{defer_after} = $args{defer_after} || 0;
return $self;
}
sub again
{
my $self = shift;
if( $self->{defer_after} and ++$self->{count} < $self->{defer_after} ) {
my $code = shift;
# args still in @_
goto &$code;
}
$self->later( @_ );
}
sub later
{
my $self = shift;
push @{ $self->{queue} }, [ @_ ];
}
=head1 METHODS
=cut
=head2 $pending = $gov->is_pending
Returns true if at least one code reference has been stored that hasn't yet
been invoked.
=cut
sub is_pending
{
my $self = shift;
return $self->{queue} && @{ $self->{queue} } > 0;
}
=head2 $gov->prod
Invokes all of the currently-stored code references, in the order they were
stored. If any new references are stored by these, they will not yet be
invoked, but will be available for the next time this method is called.
=cut
sub prod
{
my $self = shift;
$self->{count} = 0;
my $queue = $self->{queue};
$self->{queue} = [];
foreach my $item ( @$queue ) {
my ( $code, @args ) = @$item;
$code->( @args );
}
}
=head2 $gov->flush
Repeatedly calls C<prod> until no more code references are pending.
=cut
sub flush
{
my $self = shift;
$self->prod while $self->is_pending;
}
=head1 SUBCLASS METHODS
The following methods are used internally to implement the functionality,
which may be useful to implementors of subclasses.
=cut
=head2 $gov->later( $code, @args )
Used to enqueue the C<$code> ref to be invoked later with the given C<@args>,
once it is determined this should be deferred (rather than being invoked
immediately in the case of the first few invocations when C<defer_after> is
set).
=cut
=head1 AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
=cut
0x55AA;
lib/CPS/Governor/Simple.pm view on Meta::CPAN
# You may distribute under the terms of either the GNU General Public License
# or the Artistic License (the same terms as Perl itself)
#
# (C) Paul Evans, 2009 -- leonerd@leonerd.org.uk
package CPS::Governor::Simple;
use strict;
use warnings;
use base qw( CPS::Governor );
our $VERSION = '0.19';
=head1 NAME
C<CPS::Governor::Simple> - iterate immediately as fast as possible
=head1 SYNOPSIS
use CPS qw( gkforeach );
use CPS::Governor::Simple;
my $gov = CPS::Governor::Simple->new;
gkforeach( $gov, [ 1 .. 10 ],
sub {
my ( $item, $knext ) = @_;
print "$item\n";
goto &$knext;
},
sub {},
);
=head1 DESCRIPTION
This L<CPS::Governor> allows the functions using it to run as fast as
possible. It invokes its continuations immediately using a tailcall, so as not
to let the stack grow arbitrarily.
Its constructor takes no special arguments, and it provides no other methods
beyond those of C<CPS::Governor>.
=cut
sub again
{
my $self = shift;
my $code = shift;
goto &$code; # intentionally leave @_ alone
}
=head1 AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
=cut
0x55AA;
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use_ok( 'CPS' );
use_ok( 'CPS::Functional' );
use_ok( 'CPS::Governor' );
use_ok( 'CPS::Governor::Simple' );
use_ok( 'CPS::Governor::Deferred' );
done_testing;
t/01kloop.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kloop );
my $poke;
my @nums;
my $num = 1;
kloop(
sub {
my ( $knext, $klast ) = @_;
push @nums, $num;
$num++;
$poke = ( $num == 3 ) ? $klast : $knext;
},
sub {
push @nums, "finished";
},
);
is_deeply( \@nums, [ 1 ], 'kloop async - @nums initially' );
$poke->();
is_deeply( \@nums, [ 1, 2 ], 'kloop async - @nums after first poke' );
$poke->();
is_deeply( \@nums, [ 1, 2, "finished" ], 'kloop async - @nums after second poke' );
@nums = ();
our $nested = 0;
kloop(
sub {
my ( $knext, $klast ) = @_;
is( $nested, 0, "kloop sync call does not nest for $num" );
local $nested = 1;
push @nums, $num;
$num++;
( ( $num == 5 ) ? $klast : $knext )->();
},
sub {
push @nums, "finished";
},
);
is_deeply( \@nums, [ 3, 4, "finished" ], 'kloop sync - @nums initially' );
my @result;
kloop(
sub {
my ( $knext, $klast ) = @_;
$klast->( 1, 2, 3 );
},
sub {
push @result, @_;
}
);
is_deeply( \@result, [], 'kloop clears @_ in $klast' );
done_testing;
t/02kforeach.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kforeach );
my @nums;
kforeach(
[ 1, 2, 3 ],
sub {
my ( $item, $knext ) = @_;
push @nums, $item;
$knext->();
},
sub {
push @nums, "finished";
},
);
is_deeply( \@nums, [ 1, 2, 3, "finished" ], 'kforeach sync - @nums' );
@nums = ();
kforeach(
[ 4, 5, 6, 7 ],
sub {
my ( $item, $knext, $klast ) = @_;
goto &$klast if $item == 6;
push @nums, $item;
$knext->();
},
sub {
push @nums, "finished";
},
);
is_deeply( \@nums, [ 4, 5, "finished" ], 'kforeach sync - @nums' );
done_testing;
t/03kdescend.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kdescendd kdescendb );
my $ret;
$ret = "";
kdescendd(
[ [ [ 1, 2 ], 3, [ 4 ] ], 5 ],
sub {
my ( $i, $kmore ) = @_;
return $kmore->( @$i ) if ref $i;
$ret .= $i;
$kmore->()
},
sub { }
);
is( $ret, "12345", 'kdescendd sync $ret' );
$ret = "";
kdescendb(
[ [ [ 1, 2 ], 3, [ 4 ] ], 5 ],
sub {
my ( $i, $kmore ) = @_;
return $kmore->( @$i ) if ref $i;
$ret .= $i;
$kmore->()
},
sub { }
);
is( $ret, "53124", 'kdescendb sync $ret' );
done_testing;
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kpar );
my $result = "";
kpar(
sub { $result .= "A"; shift->() },
sub { $result .= "B"; shift->() },
sub { $result .= "C"; }
);
is( $result, "ABC", 'kpar sync' );
my @pokes;
$result = "";
kpar(
sub { $result .= "A"; push @pokes, shift },
sub { $result .= "B"; push @pokes, shift },
sub { $result .= "C"; }
);
is( $result, "AB", 'kpar async before pokes' );
is( scalar @pokes, 2, '2 pokes queued' );
(shift @pokes)->();
is( $result, "AB", 'kpar async still unfinished after 1 poke' );
(shift @pokes)->();
is( $result, "ABC", 'kpar async now finished after 2 pokes' );
my @result;
kpar(
sub {
shift->( 1, 2, 3 );
},
sub {
push @result, @_;
}
);
is_deeply( \@result, [], 'kpar clears @_' );
done_testing;
t/05kpareach.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kpareach );
my $result = "";
kpareach(
[ "A", "B" ],
sub { $result .= shift; shift->() },
sub { $result .= "C"; }
);
is( $result, "ABC", 'kpareach sync' );
my @pokes;
$result = "";
kpareach(
[ "A", "B" ],
sub { $result .= shift; push @pokes, shift },
sub { $result .= "C"; }
);
is( $result, "AB", 'kpareach async before pokes' );
is( scalar @pokes, 2, '2 pokes queued' );
(shift @pokes)->();
is( $result, "AB", 'kpareach async still unfinished after 1 poke' );
(shift @pokes)->();
is( $result, "ABC", 'kpareach async now finished after 2 pokes' );
done_testing;
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kseq );
my $result = "";
kseq(
sub { $result .= "A"; shift->() },
sub { $result .= "B"; shift->() },
sub { $result .= "C"; }
);
is( $result, "ABC", 'kseq sync' );
my @pokes;
$result = "";
kseq(
sub { $result .= "A"; push @pokes, shift },
sub { $result .= "B"; push @pokes, shift },
sub { $result .= "C"; }
);
is( $result, "A", 'kseq async before pokes' );
is( scalar @pokes, 1, '1 poke queued' );
(shift @pokes)->();
is( $result, "AB", 'kseq async still unfinished after 1 poke' );
(shift @pokes)->();
is( $result, "ABC", 'kseq async now finished after 2 pokes' );
done_testing;
t/10liftk.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( liftk );
my $kadd = liftk { shift() + shift() };
is( ref $kadd, "CODE", 'liftk returns plain CODE reference' );
my $sum;
$kadd->( 1, 2, sub { $sum = shift } );
is( $sum, 3, 'liftk on BLOCK' );
sub mul { shift() * shift() };
my $kmul = liftk \&mul;
my $product;
$kmul->( 2, 3, sub { $product = shift } );
is( $product, 6, 'liftk on \&func' );
sub splitwords { split m/\s+/, $_[0] };
my $ksplitwords = liftk \&splitwords;
my @words;
$ksplitwords->( "my message here", sub { @words = @_ } );
is_deeply( \@words, [qw( my message here )], 'liftk works on list-returning functions' );
done_testing;
t/11dropk.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( dropk );
my $kadd = sub { $_[2]->( $_[0] + $_[1] ) };
my $add = dropk { } $kadd;
is( ref $add, "CODE", 'dropk returns plain CODE reference' );
my $sum = $add->( 1, 2 );
is( $sum, 3, 'dropped function returns result' );
my $later;
my $kwait = sub {
my $k = pop; my @args = @_;
$later = sub { $k->( @args ) }
};
my $identity = dropk { $later->() } $kwait;
my $result = $identity->( "hello" );
is( $result, "hello", 'idenity in scalar context' );
my @result = $identity->( 10, 20, 30 );
is_deeply( \@result, [ 10, 20, 30 ], 'identity in list context' );
done_testing;
t/20governor-simple.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS::Governor::Simple;
my $gov = CPS::Governor::Simple->new;
ok( defined $gov, 'defined $gov' );
isa_ok( $gov, "CPS::Governor", '$gov' );
my $called = 0;
$gov->again( sub { $called = 1 } );
is( $called, 1, '$called is 1 after $gov->again' );
$gov->again( sub { $called = shift }, 3 );
is( $called, 3, '$called is 3 after $gov->again with arguments' );
my $poke;
$gov->enter( sub { $called = 4; $poke = shift; }, sub { $called = 5 } );
is( $called, 4, '$called is 4 after $gov->enter storing kleave' );
$poke->();
is( $called, 5, '$called is 5 after invoking stored kleave' );
done_testing;
t/21governor-deferred.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS::Governor::Deferred;
my $gov = CPS::Governor::Deferred->new;
ok( defined $gov, 'defined $gov' );
isa_ok( $gov, "CPS::Governor", '$gov' );
ok( !$gov->is_pending, '$gov not yet pending' );
my $called = 0;
$gov->again( sub { $called = 1 } );
ok( $gov->is_pending, '$gov now pending' );
is( $called, 0, '$called still 0' );
$gov->prod;
ok( !$gov->is_pending, '$gov no longer pending after prod' );
is( $called, 1, '$called is 1 after prod' );
$gov->again( sub {
$called = 2;
$gov->again( sub {
$called = 3;
} );
} );
$gov->prod;
ok( $gov->is_pending, '$gov is still pending after again-in-again' );
is( $called, 2, '$called is 2 after-in-again' );
$gov->prod;
ok( !$gov->is_pending, '$gov no longer pending after inner again' );
is( $called, 3, '$called is 3 after inner again' );
$gov->again( sub {
$called = 4;
$gov->again( sub {
$called = 5;
} );
} );
$gov->flush;
ok( !$gov->is_pending, '$gov no longer pending after flush' );
is( $called, 5, '$called is 5 after flush' );
$gov = CPS::Governor::Deferred->new( defer_after => 3 );
$called = 0;
sub more
{
$called >= 6 and return;
$called++;
$gov->again( \&more );
}
more();
is( $called, 3, '$called is 3 after first again' );
$gov->prod;
is( $called, 6, '$called is 6 after poke' );
done_testing;
t/30governor.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( gkwhile gkforeach );
use CPS::Governor::Simple;
my $gov = CPS::Governor::Simple->new;
my $count = 0;
gkwhile( $gov, sub { ++$count < 5 ? $_[0]->() : $_[1]->() }, sub {} );
is( $count, 5, '$count is 5 after gkwhile' );
$count = 0;
gkforeach( $gov, [ 1 .. 5 ], sub { ++$count; $_[1]->() }, sub {} );
is( $count, 5, '$count is 5 after gkforeach' );
done_testing;
t/31caller.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kloop kforeach gkforeach );
eval { require Sub::Name } or
plan skip_all => "No Sub::Name";
sub callers
{
my @pkgs;
my $i = 1;
push @pkgs, (caller $i)[3] and $i++ while (caller $i)[3];
@pkgs;
}
my $count = 0;
my @callers;
kloop( sub {
my ( $knext, $klast ) = @_;
push @callers, [ callers ];
++$count == 3 ? $klast->() : $knext->();
}, sub {} );
is_deeply( \@callers,
[
[ 'main::__ANON__', 'CPS::Governor::enter', 'CPS::gkloop' ],
[ 'main::__ANON__', 'CPS::Governor::enter', 'CPS::gkloop' ],
[ 'main::__ANON__', 'CPS::Governor::enter', 'CPS::gkloop' ],
],
'@callers after kloop' );
@callers = ();
kforeach( [ 1 .. 3 ], sub {
my ( $i, $knext ) = @_;
push @callers, [ callers ];
$knext->();
}, sub {} );
is_deeply( \@callers,
[
[ 'main::__ANON__', 'CPS::Governor::enter', 'CPS::gkloop', 'CPS::gkforeach' ],
[ 'main::__ANON__', 'CPS::Governor::enter', 'CPS::gkloop', 'CPS::gkforeach' ],
[ 'main::__ANON__', 'CPS::Governor::enter', 'CPS::gkloop', 'CPS::gkforeach' ],
],
'@callers after kforeach' );
my $gov = TestGovernor->new;
@callers = ();
gkforeach( $gov, [ 1 .. 3 ], sub {
my ( $i, $knext ) = @_;
push @callers, [ callers ];
$knext->();
}, sub {} );
$gov->poke while $gov->pending;
is_deeply( \@callers,
[
[ 'main::__ANON__', 'TestGovernor::poke' ],
[ 'main::__ANON__', 'TestGovernor::poke' ],
[ 'main::__ANON__', 'TestGovernor::poke' ],
],
'@callers after gkforeach on deferred governor' );
done_testing;
package TestGovernor;
use base qw( CPS::Governor );
sub again
{
my $self = shift;
my ( $code, @args ) = @_;
$self->{code} = $code;
$self->{args} = \@args;
}
sub pending
{
my $self = shift;
return defined $self->{code};
}
sub poke
{
my $self = shift;
my $code = delete $self->{code} or die;
$code->( @{ delete $self->{args} } );
}
t/32leakcheck.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS qw( kwhile );
if( $] < 5.008 ) {
plan skip_all => "weaken() doesn't work before 5.8";
}
my $destroycount = 0;
my $poke;
{
my $obj = DestroyCounter->new( \$destroycount );
my $callcount = 0;
kwhile(
sub {
my ( $knext, $klast ) = @_;
$callcount++;
# Just so this closure references the variable
$obj = $obj;
return $klast->() if $callcount == 3;
$poke = $knext;
},
sub {
}
);
}
is( $destroycount, 0, 'Initially undestroyed' );
$poke->();
is( $destroycount, 0, 'Undestroyed after first poke' );
$poke->();
undef $poke;
is( $destroycount, 1, 'Destroyed after second poke' );
done_testing;
package DestroyCounter;
sub new
{
my $class = shift;
my ( $varref ) = @_;
bless [ $varref ], $class;
}
sub DESTROY
{
my $self = shift;
${ $self->[0] }++;
}
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS::Functional qw( kmap );
my @nums;
kmap(
[ 1, 2, 3 ],
sub {
my ( $item, $k ) = @_;
$k->( $item * 2 );
},
sub {
@nums = @_;
},
);
is_deeply( \@nums, [ 2, 4, 6 ], 'kmap sync - @nums' );
@nums = ();
done_testing;
t/41kgrep.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS::Functional qw( kgrep );
my @nums;
kgrep(
[ 1, 2, 3, 4 ],
sub {
my ( $item, $k ) = @_;
$k->( $item % 2 == 0 );
},
sub {
@nums = @_;
},
);
is_deeply( \@nums, [ 2, 4 ], 'kgrep sync - @nums' );
@nums = ();
done_testing;
t/42kfold.t view on Meta::CPAN
#!/usr/bin/perl
use strict;
use warnings;
use Test::More;
use CPS::Functional qw( kfoldl kfoldr );
my $ret;
kfoldl(
[ 1, 2, 3 ],
sub {
my ( $left, $right, $k ) = @_;
$k->( "($left+$right)" );
},
sub {
$ret = shift;
},
);
is( $ret, "((1+2)+3)", 'kfoldl sync - @nums' );
kfoldr(
[ 1, 2, 3 ],
sub {
my ( $left, $right, $k ) = @_;
$k->( "($left+$right)" );
},
sub {
$ret = shift;
},
);
is( $ret, "(1+(2+3))", 'kfoldr sync - @nums' );
done_testing;
( run in 0.652 second using v1.01-cache-2.11-cpan-73692580452 )