I realize this is a very old thread, but I just found it and was wondering about the efficiency of this. I understand you could have a long, complicated expression with no room for if statements, with [ $x => $y ] -> [ $x <= $y ] as just a small portion of that expression and the example of my $highestvalue is just a simple example. However if you were in a loop, and just wanted to keep overwriting $highestvalue every time you find a higher value, wouldn't it be better to write it this way?:

my $x = 0;
foreach $y (@lots_of_values){
   $x = $y if $y > $x;
}
return $x;
[download]

Is that just as efficient as writing it this way?:

my $x = 0;
foreach $y (@lots_of_values){
   $x = [ $x => $y ] -> [ $x <= $y ];
}
return $x;
[download]

The second way seems overly complicated in this case.