Before I show the code, let me tell you a few of the other names people have suggested for this module: Personally, my favorite is BlockF::cker, but that wouldn't go over very well with the masses now, would it?

So right now, it's called Ensure. Here's a sample use: 

use Ensure;
use strict;

my ($x,$limit) = (0,100);

ensure { $x < $limit } using($x), looping {
  print "Enter P,Q,R: ";
  chomp(my $numbers = <STDIN>);
  my ($p,$q,$r) = split /,/, $numbers;
  
  $x += $p;
  $x *= $q;
  $x /= $r;
};

print "Finally stopped at $x.\n";

[download]
What this code has saved me from doing is: 
while ($x < $limit) {
  print "Enter P,Q,R: ";
  chomp(my $numbers = <STDIN>);
  my ($p,$q,$r) = split /,/, $numbers;
  
  $x += $p;
  last if $x >= $limit;
  $x *= $q;
  last if $x >= $limit;
  $x /= $r;
}

[download]
The point is that the module tracks accesses and modifications to a given list of variables, and will execute a conditional expression at each point. As soon as the condition is false, it stops the loop.

This is synonymous to walking around the block several times, and AS SOON as you see merlyn, you let me know. You don't wait to finish your current circuit, you tell me immediately.

Update: Here are some sample uses of the using() function: 

ensure { ... } using($x,$y,$z), looping { ... };

ensure { ... } using($x,\@y), looping { ... };

ensure { ... } using($x,\%y,\@z), looping { ... };

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Basically, scalars can be sent as-is. Arrays and hashes must be passed by reference. That's just the way it is. So here's the bloody code. 
package Ensure;


use strict;
require Exporter;

@Ensure::ISA = qw( Exporter );
@Ensure::EXPORT = qw( ensure using looping );


sub ensure (&@) {
  my ($cref, $obj, $loop) = @_;
  for (@$obj) {
    if (not ref $$_) { tied($$_)->[1] = $cref }
    elsif (ref $$_ eq 'SCALAR') { tied($$$_)->[1] = $cref }
    elsif (ref $$_ eq 'ARRAY') { tied(@$$_)->[1] = $cref }
    else { tied(%$$_)->[1] = $cref }
  }
  eval { { $loop->(); redo } };
  die $@ if $@ ne "[Ensure]\n";
  untie $$_ for @$obj;
}


sub using (@) {
  my @obj;
  for (@_) {
    if (not ref) { tie $_, 'Ensure::Scalar' => $_ }
    elsif (ref eq 'SCALAR') { tie $$_, 'Ensure::Scalar' => $$_ }
    elsif (ref eq 'ARRAY') { tie @$_, 'Ensure::Array' => @$_ }
    elsif (ref eq 'HASH') { tie %$_, 'Ensure::Hash' => %$_ }
    else { next }
    push @obj, \$_;
  }
  return \@obj;
}


sub looping (&) { $_[0] }


package Ensure::Scalar;

sub TIESCALAR {
  my ($class, $val) = @_;
  bless [ $val ], $class;
}

sub FETCH {
  my $self = shift;
  my $val = $self->[0];
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub STORE {
  my ($self, $val) = @_;
  $self->[0] = $val;
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}


package Ensure::Array;

sub TIEARRAY {
  my $class = shift;
  bless [ [ @_ ] ], $class;
}

sub FETCH {
  my ($self, $i) = @_;
  my $val = $self->[0][$i];
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub FETCHSIZE {
  my $self = shift;
  my $size = @{ $self->[0] };
  die "[Ensure]\n" unless $self->[1]->();
  return $size;
}

sub STORE {
  my ($self, $i, $val) = @_;
  $self->[0][$i] = $val;
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub STORESIZE {
  my ($self, $size) = @_;
  $#{ $self->[0] } = $size;
  die "[Ensure]\n" unless $self->[1]->();
  return $size;
}

sub EXISTS {
  my ($self, $i) = @_;
  my $val = exists $self->[0][$i];
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub DELETE {
  my ($self, $i) = @_;
  my $val = delete $self->[0][$i];
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub PUSH {
  my $self = shift;
  for (@_) {
    push @{ $self->[0] }, $_;
    die "[Ensure]\n" unless $self->[1]->();
  }
  return scalar @{ $self->[0] };
}

sub POP {
  my $self = shift;
  my $val = pop @{ $self->[0] };
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub UNSHIFT {
  my $self = shift;
  for (reverse @_) {
    unshift @{ $self->[0] }, $_;
    die "[Ensure]\n" unless $self->[1]->();
  }
  return scalar @{ $self->[0] };
}

sub SHIFT {
  my $self = shift;
  my $val = shift @{ $self->[0] };
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub CLEAR {
  my $self = shift;  
  $self->[0] = [];
  die "[Ensure]\n" unless $self->[1]->();
  return;
}


package Ensure::Hash;

sub TIEHASH {
  my $class = shift;
  bless [ { @_ } ], $class;
}

sub FETCH {
  my ($self, $key) = @_;
  my $val = $self->[0]{$key};
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub STORE {
  my ($self, $key, $val) = @_;
  $self->[0]{$key} = $val;
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub FIRSTKEY {
  my $self = shift;
  my ($k,$v) = each %{ $_[0][0] };
  die "[Ensure]\n" unless $self->[1]->();
  return wantarray ? ($k,$v) : $k;
}

sub NEXTKEY {
  my $self = shift;
  my ($k,$v) = each %{ $_[0][0] };
  die "[Ensure]\n" unless $self->[1]->();
  return wantarray ? ($k,$v) : $k;
}

sub EXISTS {
  my ($self,$key) = @_;
  my $val = exists $self->[0]{$key};
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub DELETE {
  my ($self, $key) = @_;
  my $val = delete $self->[0]{$key};
  die "[Ensure]\n" unless $self->[1]->();
  return $val;
}

sub CLEAR {
  my $self = shift;  
  $self->[0] = {};
  die "[Ensure]\n" unless $self->[1]->();
  return;
}


1;

[download]

In reply to Help Name This Module by japhy

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