NAME

contextLimitedPowers.pl - Restrict the base or power allowed in exponentials.

DESCRIPTION

Implements subclasses of the "^" operator that restrict the base or power that is allowed. There are four available restrictions:

• No raising e to a power

  LimitedPowers::NoBaseE();

• Only allowing integer powers (positive or negative)

  LimitedPowers::OnlyIntegers();

• Only allowing positive integer powers

  LimitedPowers::OnlyPositiveIntegers();

• Only allowing positive integer powers (and 0)

  LimitedPowers::OnlyNonNegativeIntegers();

Only one of the three can be in effect at a time; setting a second one overrides the first.

These function affect the current context, or you can pass a context reference, as in

$context = Context("Numeric")->copy;
LimitedPowers::OnlyIntegers($context);

For the integer power functions, you can pass additional parameters that control the range of values that are allowed for the powers. The oprtions include:

minPower => m

only integer powers bigger than or equal to m are allowed. (If m is undef, then there is no minimum power.)

maxPower => M

only integer powers less than or equal to M are allowed. (If M is undef, then there is no maximum power.)

message => "text"

a description of the type of power allowed (e.g., "positive integer constants");

checker => code

a reference to a subroutine that will be used to check if the powers are acceptable. It should accept a reference to the BOP::power structure and return 1 or 0 depending on whether the power is OK or not.

For example:

LimitedPowers::OnlyIntegers(
    minPower => -5, maxPower => 5,
    message => "integer constants between -5 and 5",
);

would accept only powers between -5 and 5, while

LimitedPowers::OnlyIntegers(
    checker => sub {
        return 0 unless LimitedPowers::isInteger(@_);
        my $self = shift; my $p = shift; # the power as a constant
        return $p != 0 && $p != 1;
    },
    message => "integer constants other than 0 or 1",
);

would accept any integer power other than 0 and 1.