Since closures are just another way of implementing encapsulation and re-use, I think it would behoove the programmer to choose the most appropriate elements of the program to refactor using this technique. In the case of your example, I think a better choice would be to "higher-order"ify the file accessing bits, since that's the most general-purpose part, and is likely to have the greater pay-off in terms of re-use. That's not to say that a max() function couldn't as well, but it seems to me to be the more application-specific algorithmic part.
in reply to How A Function Becomes Higher Order
Btw - I don't get the argument that named parameters aid extensibility. I frankly don't see any extensibility in this mechanism. Can you show how it would be done?
my( $filename, $each_line_cb ) = @_;
my $fh = new IO::File "< $filename" or die "read $filename - $!";
chomp, $each_line_cb->($_) while <$fh>;
my( $score ) = @_;
!defined $max || $max < $score and $max = $score;