a monad extension for AE::cv
Latest commit 9f154f5 Mar 23, 2014 @hiratara 0.06



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


use Data::Monad::CondVar;

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


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.


  • $cv = as_cv($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->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.









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