Another way to fix the problem if you do really want to use prototypes is to declare them before you use them (although I do agree with ikegami that it is probably better not to use them in the first place):

use strict;
sub higherLevel(\@);
sub showArray(\@);

sub higherLevel(\@)
  {
  my(@arr) = @{(shift)};
  showArray(@arr);
  }
sub showArray(\@)
  {
  my(@arr) = @{(shift)};
  my($temp);
  foreach $temp (@arr) { print "$temp\n"; }
  }
my(@arr) = ("one","two","three");
higherLevel(@arr);
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