I've been working through examples in MJD's Higher Order Perl and hit a snag. This code from Chapter 4 works fine: 
# This software is Copyright 2005 by Elsevier Inc.  You may use it
# under the terms of the license at http://perl.plover.com/hop/LICENSE
+.txt .
###
### upto
###

## Chapter 4 section 2.1

sub upto {
  my ($m, $n) = @_;
  return sub {
    return $m <= $n ? $m++ : undef;
  };
}
my $it = upto(3,5);
my $value->it();
print "$value\n";

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However, when I sweeten the function as suggested in the text: 
sub upto {
  my ($m, $n) = @_;
  return Iterator {
    return $m <= $n ? $m++ : undef;
  };
}
sub Iterator (&) { return $_[0]; }

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I get a failure: Undefined subroutine &main::3 called
They laughed at Joan of Arc, but she went right ahead and built it. --Gracie Allen

In reply to Basic question about Iterator code by adamsj

Title:
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