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retiring wantarray?

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From:
Yuval Kogman
Date:
March 17, 2005 04:51
Subject:
retiring wantarray?
Message ID:
20050317125120.GA17284@woobling.org
Hola...

This message is not about removing wantarray, but finding a better
solution for a typical but annoying usage-idiom.

sub value_added { # not really a wrapper
	my $result = original(@args);
	...
	return $result;
}

Is a typically broken subroutine in perl 5, unless original() never
returns lists. Usually people use wantarray, or if they're being
even more politically correct, they use Want, but this is an
annoying overhead.

What are perl6's solutions towards making this easier? I tend to
design around this, normally returning lists, unless the sub name
implies singularity.

Here are some ideas:

# i don't like this one, it complicates things
sub value_added {
	original(@args); # return is collected here
} after { # but just before leaving, this is done:
	... # how do we access the return? what can you do here?
}

# this seems nicer, but very ad-hoc
sub value_added {
	return_later(original(@argS);
	...	
	# with no explicit return or return later, the return_later is
	# returned, instead of the last expression's result
}

# this is my favourite
sub value_added {
	$return is context_sensitive = original(@args); # hides wantarray magic

	... # you can ask $return what it's context is
	# but it pretends to be just a normal value anyway (array ref in
	# list, etc). How do you modify it, without breaking it?
	# implicit strong type?

	$return; # magically unwraps
}

# or in perl5, maybe it could be done like:
sub value_added {
	my $return = Returner::Smart->new(sub { original(@args) });
	# Returner is an object that does Want based lookups
	...
	$returner->return; # could this do lvalue crap?
}

-- 
 ()  Yuval Kogman <nothingmuch@woobling.org> 0xEBD27418  perl hacker &
 /\  kung foo master: /me does a karate-chop-flip: neeyah!!!!!!!!!!!!!!


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