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I think that upto(...) returns an iterator/generator. The example I used is fairly trivial to reimplement in Perl5 now already:

# perl 5.10 sub ENDOFITERATION { undef }; # some magic value that signals the end +of all values sub upto { my $start = 0; my $stop = shift; return sub { if ($start < $stop) { return $start++ } else { return ENDOFITERATION }; }; };

Iterators/generators allow you to conveniently program in a linear fashion without needing to maintain the state. For example this contrived example is far easier to write in a linear fashion than it is in a closure fashion, because you need to store the current point of execution:

# Read incoming commands - an infinite loop/generator sub get_commands { while (<>) { yield $_; }; }; sub user_session { COMMAND: { my $command = get_commands; # read one command if ($command =~ /^login (\w+)/) { my $user = $1; my $pass = get_commands; # read next line if ($user_db{$user} ne $pass) { print "User $user rejected.\n"; redo COMMAND; } else { for my $command (get_commands) { if ($command =~ /^logout/) { return } else { yield [$user, $command] }; }; }; } else { # not logged in }; }; }; sub process_sessions { for my $line (user_session()) { my ($user,$command) = @$line; print "$user: Executing $command\n"; }; };

I'm aware that all my wishes are possible in principle now already, but either slow or burdened with ugly syntax. Which is why I wish for them to become less burdened and faster.


In reply to Re^3: what would you like to see in perl5.12? by Corion
in thread what would you like to see in perl5.12? by ysth

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