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Number::Tolerant - tolerance ranges for inexact numbers |
Number::Tolerant - tolerance ranges for inexact numbers
version 1.550
$Id: /my/cs/projects/tolerant/trunk/lib/Number/Tolerant.pm 22321 2006-05-19T02:29:23.338118Z rjbs $
use Number::Tolerant;
my $range = tolerance(10 => to => 12); my $random = 10 + rand(2);
die "I shouldn't die" unless $random == $range;
print "This line will always print.\n";
Number::Tolerant creates a number-like object whose value refers to a range of possible values, each equally acceptable. It overloads comparison operations to reflect this.
I use this module to simplify the comparison of measurement results to specified tolerances.
reject $product unless $measurement == $specification;
There is a new method on the Number::Tolerant class, but it also exports a
simple function, tolerance, which will return an object of the
Number::Tolerant class. Both use the same syntax:
my $range = Number::Tolerant->new( $x => $method => $y);
my $range = tolerance( $x => $method => $y);
The meaning of $x and $y are dependant on the value of $method, which
describes the nature of the tolerance. Tolerances can be defined in five ways,
at present:
method range -------------------+------------------ plus_or_minus | x +/- y plus_or_minus_pct | x +/- (y% of x) or_more | x to Inf or_less | x to -Inf more_than | x to Inf, not x less_than | x to -Inf, not x to | x to y infinite | -Inf to Inf offset | (x + y1) to (x + y2)
For or_less and or_more, $y is ignored if passed. For infinite,
neither $x nor $y is used; ``infinite'' should be the sole argument. The
first two arguments can be reversed for more_than and less_than, to be
more English-like.
Offset tolerances are slightly unusual. Here is an example:
my $offset_tolerance = tolerance(10 => offset => (-3, 5)); # stringifies to: 10 (-3 +5)
An offset is very much like a plus_or_minus tolerance, but its center value
is not necessarily the midpoint between its extremes. This is significant for
comparisons and numifications of the tolerance. Given the following two
tolerances:
my $pm_dice = tolerance(10.5 => plus_or_minus => 7.5); my $os_dice = tolerance(11 => offset => (-8, 7));
The first will sort as numerically less than the second.
A new tolerance can be instantiated from the stringification of an old tolerance. For example:
my $range = Number::Tolerant->from_string("10 to 12");
die "Everything's OK!" if 11 == $range; # program dies of joy
This will not yet parse stringified unions, but that will be implemented in the future. (I just don't need it yet.)
my $string = $tolerance->stringify_as($type);
This method does nothing! Someday, it will stringify the given tolerance as a
different type, if possible. ``10 +/- 1'' will
stringify_as('plus_or_minus_pct') to ``10 +/- 10%'' for example.
my $n = $tolerance->numify;
This returns the numeric form of a tolerance. If a tolerance has both a minimum and a maximum, and they are the same, then that is the numification. Otherwise, numify returns undef.
Tolerances overload a few operations, mostly comparisons.
/numify.
infinite - "any number" to - "m <= x <= n" or_more - "m <= x" or_less - "x <= n" more_than - "m < x" less_than - "x < n" offset - "x (-y1 +y2)" constant - "x" plus_or_minus - "x +/- y" plus_or_minus_pct - "x +/- y%"
A number is less than a tolerance if it is less than its minimum value.
No number is greater than an ``or_more'' tolerance or less than an ``or_less'' tolerance.
``...or equal to'' comparisons include the min/max values in the permissible range, as common sense suggests.
& a tolerance or number is the intersection of the two ranges.
Intersections allow you to quickly narrow down a set of tolerances to the most
stringent intersection of values.
tolerance(5 => to => 6) & tolerance(5.5 => to => 6.5); # this yields: tolerance(5.5 => to => 6)
If the given values have no intersection, () is returned.
An intersection with a normal number will yield that number, if it is within the tolerance.
| a tolerance or number is the union of the two. Unions allow
multiple tolerances, whether they intersect or not, to be treated as one. See
the Number::Tolerant::Union manpage for more information.
This feature is slighly experimental, but it's here.
New tolerance types may be written as subclasses of the Number::Tolerant::Type manpage, providing the interface described in its documentation. They can then be enabled or disabled with the following methods:
enable_plugin Number::Tolerant->enable_plugin($class_name);
This method enables the named class, so that attempts to create new tolerances
will check against this class. Classes are checked against
/validate_plugin before being enabled. An exception is thrown if the
class does not appear to provide the Number::Tolerant::Type interface.
disable_plugin Number::Tolerant->disable_plugin($class_name);
This method will disable the named class, so that future attempts to create new tolerances will not check against this class.
validate_plugin Number::Tolerant->validate_plugin($class_name);
This method checks (naively) that the given class provides the interface defined in Number::Tolerant::Type. If it does not, an exception is thrown.
from_string to cover unions.from_string to include Number::Range-type specifications.
my $range = tolerance(9 => to => 17);
my $range_pm = $range->convert_to('plus_minus');
$range->stringify_as('plus_minus_pct');
The module the Number::Range manpage provides another way to deal with ranges of
numbers. The major differences are: N::R is set-like, not range-like; N::R
does not overload any operators. Number::Tolerant will not (like N::R) attempt
to parse a textual range specification like ``1..2,5,7..10'' unless specifically
instructed to. (The valid formats for strings passed to from_string does
not match Number::Range exactly. See TODO.)
The Number::Range code:
$range = Number::Range->new("10..15","20..25");
Is equivalent to the Number::Tolerant code:
$range = Number::Tolerant::Union->new(10..15,20..25);
...while the following code expresses an actual range:
$range = tolerance(10 => to => 15) | tolerance(20 => to => 25);
Thanks to Yuval Kogman and #perl-qa for helping find the bizarre bug that drove the minimum required perl up to 5.8
Thanks to Tom Freedman, who reminded me that this code was fun to work on, and also provided the initial implementation for the offset type.
Ricardo SIGNES, <rjbs@cpan.org>
(C) 2004-2006, Ricardo SIGNES. Number::Tolerant is available under the same terms as Perl itself.
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Number::Tolerant - tolerance ranges for inexact numbers |