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use constant EARTH_RADIUS => 3956;
use constant PI           => 4 * atan2 1, 1;

...
  return sub { abs($lat - $_[0]) < $maxlatdiff and 
               abs($long - $_[1]) < $maxlongdiff; }
}

# zipcode, lat, long
@data = (['00210', 43.00589, 71.0132], ['00211', 43.00589, 71.0132], .
+..);

map { $_->[1] *= PI/180; $_->[2] *= PI / 180;} @data;

$distance = 25;

for $i (0..$#data) {
...
    }
  }
}

@distances = qw(5 10 25 50 100);
@distfiles = map { "0-$_.txt" } @distances;

...
    }
  }
}