@foo = ( 7, 12, 3, 11, 1 );
sub by_number
{
	if ( $a < $b ) { -1; }
	elsif ( $a == $b ) { 0; }
	elsif ( $a > $b ) { 1; }
}
@foo = sort by_number @foo;

sub by_number { $a <=> $b; }
@foo = sort by_number @foo;

@foo = sort { $a <=> $b; } @foo;
# This is an un-named subroutine!