With apologies to Zaxo for continuing to use boolean operators to construct switch statements, I'd appreciate any comments on this code. The sub uFIFO {} rather than the test code below it.

I'd also appreciate any pointers on why the last line of the while loop does nothing?

And the best way of debugging the problem?

Thanks.

#! perl -w
use strict;

sub uFIFO {
    my (%fifo, @fifo);
    my $next = 0;
    return sub {
            # no parameters - return the next value or reset the itera
+tor and return undef if its the last.
        !@_ and return (scalar @fifo && $next < @fifo) ? ${$fifo[$next
+++]} : ($next=0, undef)

            # we have parameters and the first one is defined,
            # push any defined values not already in the list and retu
+rn the count of them
        or       defined $_[0]  and return scalar map{  
                                            defined $_  && !exists $fi
+fo{$_} 
                                            and push @fifo, \($fifo{ $
+_ } = $_) 
                                             } @_

            # We only get this far if the first value is undef!
            # reset iterator
        or    lc($_[1]) eq 'reset'  and $next = 0

            # return all values possibly random order
        or     lc($_[1]) eq 'all' and return keys %fifo

            # return all values possibly random order
        or     lc($_[1]) eq 'ordered' and return map { ${ $_ } } @fifo

            # for testing only
        or     lc($_[1]) eq 'dump' and return @fifo
        ;
    }
}

my $fifo1 = uFIFO(); # create a fifo - we can have as many as we need

# create some test data and shuffle it
my @test = ('a' .. 'z', 'i' .. 'r');
($a=$_+rand @test-$_) and @test[$_,$a] = @test[$a,$_] for (0..$#test);

printf "%15.15s: %s\n", 'Initial data', "@test"; # data in original or
+der for comparison later

$fifo1->( $_ ) for @test; #add some test data

# Show only one copy of each made it in
print sprintf( "%15.15s: ", 'Added'), "@{[$fifo1->( undef, 'all')]}   
+ ", $/; 

# process the list, randomly adding some more and printing them out as
+ we process
my $i;
printf '%15.15s: ', 'Processed';
while( my $temp= $fifo1->() ) {
    print $temp, ' ' ;
    (0 == int(rand 4)) and $fifo1->( ++$i ); # Randomly add new values
    (0 == int(rand 4)) and $fifo1->( chr(97+rand 26) ); # nothing happ
+ens here????
}
print $/;

print sprintf( "%15.15s: ", 'Ordered'), "@{ [ $fifo1->(undef, 'ordered
+') ] }", $/;    
print sprintf("%15.15s: ", 'Unordered'), "@{ [ $fifo1->(undef, 'all') 
+] }"    , $/;         

__END__
#output
C:\test>193450
   Initial data: j h m q f l a w p k u b d n t o r i k o q s l p c x y
+ n i m r z e g v j
          Added: a b c d e f g h i j k l m n o p q r s t u v w x y z
      Processed: j h m q f l a w p k u b d n t o r i s c x y z e g v 1
+ 2 3 4 5 6 7 8 9 10 11 12 13
        Ordered: j h m q f l a w p k u b d n t o r i s c x y z e g v 1
+ 2 3 4 5 6 7 8 9 10 11 12 13
      Unordered: a b c d e f g h i j k l m n 1 o 2 p 3 q 10 4 r 11 5 s
+ 12 6 t 13 7 u 8 v 9 w x y z

C:\test>
[download]