NAME

Data::Monad::CondVar - The CondVar monad.

SYNOPSIS

  use Data::Monad::CondVar;

  # The sleep sort
  my @list = (3, 5, 2, 4, 9, 1, 8);
  my @result;
  AnyEvent::CondVar->all(
      map {
          cv_unit($_)->sleep($_ / 1000)
                     ->map(sub { push @result, @_ });
      } @list
  )->recv;

DESCRIPTION

Data::Monad::CondVar adds monadic operations to AnyEvent::CondVar.

Since this module extends AnyEvent::CondVar directly, you can call monadic methods anywhere there are CondVars.

This module is marked EXPERIMENTAL. API could be changed without any notice.

METHODS

$cv = as_cv($cb->($cv))

A helper for rewriting functions using callbacks to ones returning CVs.

  my $cv = as_cv { http_get "http://google.ne.jp", $_[0] };
  my ($data, $headers) = $cv->recv;

$cv = cv_unit(@vs)

$cv = cv_zero()

$cv = cv_fail($v)

$f = cv_flat_map_multi(\&f, $cv1, $cv2, ...)

$f = cv_map_multi(\&f, $cv1, $cv2, ...)

$cv = cv_sequence($cv1, $cv2, ...)

These are shorthand of methods which has the same name.

$cv = call_cc($f->($cont))

Calls $f with current continuation, $cont. $f must return a CondVar object. If you call $cont in $f, results are sent to $cv directly and codes left in $f will be skipped.

You can use call_cc to escape a deeply nested call structure.

  sub myname {
      my $uc = shift;

      return call_cc {
          my $cont = shift;

          cv_unit("hiratara")->flat_map(sub {
              return $cont->(@_) unless $uc; # escape from an inner block
              cv_unit @_;
          })->map(sub { uc $_[0] });
      };
  }

  print myname(0)->recv, "\n"; # hiratara
  print myname(1)->recv, "\n"; # HIRATARA

unit

flat_map

Overrides methods of Data::Monad::Base::Monad.

zero

Overrides methods of Data::Monad::Base::MonadZero. It uses fail method internally.

$cv = AnyEvent::CondVar->fail($msg)

Creates the new CondVar object which represents a failed operation. You can use catch to handle failed operations.

$cv = AnyEvent::CondVar->any($cv1, $cv2, ...)

Takes the earliest value from $cv1, $cv2, ...

$cv = AnyEvent::CondVar->all($cv1, $cv2, ...)

Takes all values from $cv1, $cv2, ...

This method works completely like <Data::Monad::Base::Monad-sequence>>, but you may want use this method for better cancellation.

$cv->cancel

Cancels computations for this CV. This method just calls the call back which is set in the canceler field.

<$cv-recv>> may never return from blocking after you call cancel.

$cv->canceler($cb->())

$code = $cv->canceler

The accessor of the method to cancel. You should set this field appropriately when you create the new CondVar object.

  my $cv = AE::cv;
  my $t = AE::timer $sec, 0, sub {
      $cv->send(@any_results);
      $cv->canceler(undef); # Destroy cyclic refs
  };
  $cv->canceler(sub { undef $t });

$cv = $cv1->or($cv2)

If $cv1 croaks, or returns the CondVar object which contains values of $cv2. Otherwise it returns $cv1's values.

or would be mplus on Haskell.

$cv = $cv1->catch($cb->($@))

If $cv1 croaks, $cb is called and it returns the new CondVar object containing its result. Otherwise catch does nothing. $cb must return a CondVar object.

You can use this method to handle errors.

  cv_unit(1, 0)
  ->map(sub { $_[0] / $_[1] })
  ->catch(sub {
      my $exception = shift;
      $exception =~ /Illegal division/
          ? cv_unit(0)           # recover from errors
          : cv_fail($exception); # rethrow
  });

$cv = $cv1->sleep($sec)

Sleeps $sec seconds, and just sends values of $cv1 to $cv.

$cv = $cv1->timeout($sec)

If $cv1 doesn't compute any values within $sec seconds, $cv will be received undef and $cv1 will be canceled.

Otherwise $cv will be received $cv1's results.

$cv = $cv1->retry($max, [$pace, ], $f->(@v))

Continue to call flat_map($f) until $f returns a normal value which doesn't croak.

$max is maximum number of retries, $pace is how long it sleeps between each retry. The default value of $pace is 0.

AUTHOR

hiratara <hiratara {at} cpan.org>

SEE ALSO

Data::Monad::Base::Monad

LICENSE

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