tk::callbacks(3pm) [debian man page]

callbacks(3pm)						User Contributed Perl Documentation					    callbacks(3pm)

NAME

       Tk::callbacks - Specifying code for Tk to call.

SYNOPSIS

       One can specify a callback in one of the following ways:

       Without arguments:

	   ... => &subname, ...
	   ... => sub { ... }, ...
	   ... => 'methodname', ...

       or with arguments:

	   ... => [ &subname, args ... ], ...
	   ... => [ sub { ... }, args... ], ...
	   ... => [ 'methodname', args... ], ...

DESCRIPTION

       Perl/Tk has a callback, where Tcl/Tk has a command string (i.e. a fragment of Tcl to be executed).  A perl/Tk callback can take one of the
       following basic forms:

       o   Reference to a subroutine "&subname"

       o   Anonymous subroutine (closure) "sub { ... }"

       o   A method name 'methodname'

       Any of these can be provided with arguments by enclosing them and the arguments in []. Here are some examples:

       $mw->bind($class, "<Delete>" => 'Delete');

       This will call $widget->Delete, the $widget being provided (by bind) as the one where the Delete key was pressed.

       While having bind provide a widget object for you is ideal in many cases it can be irritating in others. Using the list form this behaviour
       can be modified:

       $a->bind("<Delete>",[$b => 'Delete']);

       because the first element $b is an object bind will call $b->Delete.

       Note that method/object ordering only matters for "bind" callbacks, the auto-quoting in perl5.001 makes the first of these a little more
       readable:

	   $w->configure(-yscrollcommand => [ set => $ysb]);
	   $w->configure(-yscrollcommand => [ $ysb => 'set' ]);

       but both will call $ysb->set(args provided by Tk)

       Another use of arguments allows you to write generalized methods which are easier to re-use:

	   $a->bind("<Next>",['Next','Page']);
	   $a->bind("<Down>",['Next','Line']);

       This will call $a->Next('Page') or $a->Next('Line') respectively.

       Note that the contents of the "[]" are evaluated by perl when the callback is created. It is often desirable for the arguments provided to
       the callback to depend on the details of the event which caused it to be executed. To allow for this callbacks can be nested using the
       "Ev(...)" "constructor".  "Ev(...)" inserts callback objects into the argument list. When perl/Tk glue code is preparing the argument list
       for the callback it is about to call it spots these special objects and recursively applies the callback process to them.

EXAMPLES

	   $entry->bind('<Return>' => [$w , 'validate', Ev(['get'])]);

	   $toplevel->bind('all', '<Visibility>', [&unobscure, Ev('s')]);

	   $mw->bind($class, '<Down>', ['SetCursor', Ev('UpDownLine',1)]);

SEE ALSO

       Tk::bind Tk::after Tk::options Tk::fileevent

KEYWORDS

       callback, closure, anonymous subroutine, bind

perl v5.14.2							    2010-05-29							    callbacks(3pm)

README(3pm)						User Contributed Perl Documentation					       README(3pm)

NAME

       AnyEvent::Callback - callback aggregator for AnyEvent watchers.

SYNOPSIS

	   use AnyEvent::Callback;

	   # usually watchers are looked as:
	   AE::something @args, sub { ... };
	   AE::something
	       @args,
	       sub { ... },    # result
	       sub { ... };    # error

	   use AnyEvent::Callback;

	   AE::something @args, CB { ... };
	   AE::something @args,
	       CB sub { ... },	   # result
		   sub { ... };    # error

	   AE::something @args,
	       CB sub { ... },	   # result
		   sub { ... },    # error
		   sub { ... };    # anyway callback

       Callback hierarchy

	   my $cbchild = $cb->CB(sub { ... });

	   ...

	   $cbchild->error('error'); # will call $cb->error('error');

       Inside Your callback You can:

	   sub my_watcher {
	       my $cb = pop;
	       my @args = @_;

	       # ...

	       $cb->error( @error );   # error callback will be called
	       # or:
	       $cb->( $value );        # result callback will be called
	   }

       Callbacks stack

	   my $cbs = CBS;

	   for (1 .. $n) {
	       AE::something @args, $cbs->cb;
	   }

	   $cbs->wait(sub {
	       for (@_) {
		   if ($_->is_error) {	   # handle one error
		       my @err = $_->errors; # or:
		       my $errstr = $_->errstr;
		   } else {		   # results
		       my @res = $_->results;
		   }
	       }

	   });

DESCRIPTION

       The module allows You to create callback's hierarchy. Also the module groups error and result callbacks into one object.

       Also the module checks if one callback was called by watcher or not.  If a watcher doesn't call result or error callback, error callback
       will be called automatically.

       Also the module checks if a callback was called reentrant. In the case the module will complain (using "carp" in Carp).

       If a watcher touches error callback and if superior didn't define error callback, the module will call error callback upwards hierarchy.
       Example:

	   AE::something @args, CB &my_watcher, &on_error;

	   sub on_error {

	   }

	   sub my_watcher {
	       my $cb = pop;

	       ...

	       the_other_watcher $cb->CB( sub { # error callback wasn't defined
		   my $cb = pop;
		   ...
		   yet_another_watcher1 $cb->CB( sub {
		       my $cb = pop;
		       ...
		       $cb->( 123 );   # upwards callback

		   });
		   yet_another_watcher2 $cb->CB( sub {
		       my $cb = pop;
		       ...

		       $cb->error( 456 );  # on_error will be called

		   });
	       });
	   }

METHODS

   'CODE' (overloaded fake method)
	   $cb->( ... );

       You can use the object as usually CODEREF.

   CB
       Creates new callback object that have binding on parent callback.

	   my $new_cb = $cb->CB(sub { ... });	# the cb doesn't catch errors

	   my $new_cb = CB(sub { ... }, sub { ... }); # the cb catches errors

	   my $new_cb = $cb->CB(sub { ... }, sub { ... }); # the same

   error
       Calls error callback. If the object has no registered error callbacks, parent object's error callback will be called.

	   $cb->error('WTF?');

COPYRIGHT AND LICENCE

	Copyright (C) 2012 by Dmitry E. Oboukhov

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.14.2							    2012-06-30							       README(3pm)