use strict;
use warnings;
use Data::Dump qw/pp/;
use Scalar::Util qw/reftype/;

sub walk {
  my ($entry,$code) =@_;
  my $type = reftype($entry);
  $type //= "SCALAR";

  if    ($type eq "HASH") {
    walk($_,$code) for values %$entry;
  }
  elsif ($type eq "ARRAY") {
    walk($_,$code) for @$entry;
  }
  elsif ($type eq "SCALAR" ) {
    $code->($_[0]);		# alias of entry
  }
  else {
    warn "unknown type $type";
  }
}


my $test = { a => [2, 3, [4, { b => 42 }]], c => 5 };

pp $test;
walk $test, sub { $_[0]+=100 };
pp $test;