Hello,
I'd vote for the OO-style.
My reason is that the major criteria should be the reader perspective.
It should be as clear as possible what's going on in the main code
even if the reader doesn't know the hottest p6 tricks!
What you are doing here is: two operations on the same thing (the pidfile).
So the code should point out that it works twice on the same thing.
I think it's best to have an object to show this
whereas returning the sub/closure feels a bit confusing.
Your right, this style is busy work, but it's not pointless.
I would suggest a locally visible class to bring out the
local, one time usage of that class. Btw. what is the best way to do so?
Kind regards
Stefan
--- On Thu, 1/1/09, Geoffrey Broadwell <ge...@broadwell.org> wrote:
From: Geoffrey Broadwell <ge...@broadwell.org>
Subject: Converting a Perl 5 "pseudo-continuation" to Perl 6
To: perl6-us...@perl.org, perl6-language@perl.org
Date: Thursday, January 1, 2009, 3:34 PM
In the below Perl 5 code, I refactored to pull the two halves of the PID
file handling out of init_server(), but to do so, I had to return a sub
from pid_file_handler() that acted as a "continuation". The syntax
is a
bit ugly, though. Is there a cleaner way to this in Perl 6?
######
sub init_server {
my %options = @_;
# ...
# Do top (pre-daemonize) portion of PID file handling.
my $handler = pid_file_handler($options{pid_file});
# Detach from parent session and get to clean state.
become_daemon();
# Do bottom (post-daemonize) portion of PID file handling.
$handler->();
# ...
}
sub pid_file_handler {
# Do top half (pre-daemonize) PID file handling ...
my $filename = shift;
my $basename = lc $BRAND;
my $PID_FILE = $filename || "$PID_FILE_DIR/$basename.pid";
my $pid_file = open_pid_file($PID_FILE);
# ... and return a "continuation" on the bottom half
(post-daemonize).
return sub {
$MASTER_PID = $$;
print $pid_file $$;
close $pid_file;
};
}
######
When I asked this question on #perl6, pmurias suggested using
gather/take syntax, but that didn't feel right to me either -- it's
contrived in a similar way to using a one-off closure.
pmichaud offered several possibilities (I've converted some of his
suggestions expressed as prose into code, so the errors there are mine):
1. Take advantage of Perl 6 syntax reduction to turn 'return sub {...}'
into 'return {...}' (or even just fall of the end with
'{...}', I
suppose). This is visually slightly better, but still leaves the
bottom half inside a block that merely exists to satisfy Perl, not
actually representing anything intrinsic about the problem.
2. Throw a resumable exception in the middle:
sub init_server {
# ...
pid_file_handler($options{pid_file});
become_daemon();
pid_file_handler();
# ...
}
sub pid_file_handler {
# ... top half ...
throw ResumableException;
# ... bottom half ...
}
He also suggested a variant syntax with an adverb on return:
sub pid_file_handler {
# ... top half ...
return :resumable;
# ... bottom half ...
}
I suggested a naked yield syntax:
sub pid_file_handler {
# ... top half ...
yield;
# ... bottom half ...
}
These all desugar to the same thing, of course.
3. Make become_daemon a part of pid_file_handler, or vice-versa.
I rejected both of these on the basis of separating different
things into different subs. The two tasks are only tangentially
related, and neither really seems like a subordinate op of the
other.
4. In order to keep the sub separate, but still not split the
pid_file_handler call, I came up with a variation of #3 in which
pid_file_handler takes a callback parameter:
sub init_server {
# ...
pid_file_handler($options{pid_file}, &become_daemon);
# ...
}
sub pid_file_handler($pid_file, &callback) {
# ... top half ...
callback();
# ... bottom half ...
}
That seems like a silly contortion to hide the problem, and
doesn't represent my intent well -- the pid file handler doesn't
need to send a message, it needs to yield control while waiting
for something else to happen.
5. Make a new PidHandler class and address the problem in OO fashion:
sub init_server {
# ...
my $pid_handler = PidHandler.new(file => $options{pid_file});
$pid_handler.top();
become_daemon();
$pid_handler.bottom();
#...
}
This is certainly workable, but again feels like a contrived
workaround in the same way that gather/take and return {...} do.
Plus, writing a new class and using OO/method call syntax just to
allow a sub to be "split" seems like pointless busy work. Not
as bad in Perl 6 as in Perl 5, but still.
In the end, I think I like the 'naked yield' idea best of the ones we
have so far. Any comments or other ideas? [1]
-'f
[1] Other than that I've used the word 'contrived' too many times.
:-)
