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		warnings::warn("Constant name '$name' is a Perl keyword");
	    } elsif ($forced_into_main{$name}) {
		warnings::warn("Constant name '$name' is " .
		    "forced into package main::");
	    } else {
		# Catch-all - what did I miss? If you get this error,
		# please let me know what your constant's name was.
		# Write to <rootbeer@redcat.com>. Thanks!
		warnings::warn("Constant name '$name' has unknown problems");
	    }
	}

    # Looks like a boolean
    # 		use constant FRED == fred;
    } elsif ($name =~ /^[01]?\z/) {
        require Carp;
	if (@_) {
	    Carp::croak("Constant name '$name' is invalid");
	} else {
	    Carp::croak("Constant name looks like boolean value");
	}

    } else {
	# Must have bad characters
        require Carp;
	Carp::croak("Constant name '$name' has invalid characters");
    }

    {
	no strict 'refs';
	my $full_name = "${pkg}::$name";
	$declared{$full_name}++;
	if (@_ == 1) {
	    my $scalar = $_[0];
	    *$full_name = sub () { $scalar };
	} elsif (@_) {
	    my @list = @_;
	    *$full_name = sub () { @list };
	} else {
	    *$full_name = sub () { };
	}
    }

}

1;

__END__

=head1 NAME

constant - Perl pragma to declare constants

=head1 SYNOPSIS

    use constant BUFFER_SIZE	=> 4096;
    use constant ONE_YEAR	=> 365.2425 * 24 * 60 * 60;
    use constant PI		=> 4 * atan2 1, 1;
    use constant DEBUGGING	=> 0;
    use constant ORACLE		=> 'oracle@cs.indiana.edu';
    use constant USERNAME	=> scalar getpwuid($<);
    use constant USERINFO	=> getpwuid($<);

    sub deg2rad { PI * $_[0] / 180 }

    print "This line does nothing"		unless DEBUGGING;

    # references can be constants
    use constant CHASH		=> { foo => 42 };
    use constant CARRAY		=> [ 1,2,3,4 ];
    use constant CPSEUDOHASH	=> [ { foo => 1}, 42 ];
    use constant CCODE		=> sub { "bite $_[0]\n" };

    print CHASH->{foo};
    print CARRAY->[$i];
    print CPSEUDOHASH->{foo};
    print CCODE->("me");
    print CHASH->[10];			# compile-time error

=head1 DESCRIPTION

This will declare a symbol to be a constant with the given scalar
or list value.

When you declare a constant such as C<PI> using the method shown
above, each machine your script runs upon can have as many digits
of accuracy as it can use. Also, your program will be easier to
read, more likely to be maintained (and maintained correctly), and
far less likely to send a space probe to the wrong planet because
nobody noticed the one equation in which you wrote C<3.14195>.

=head1 NOTES

The value or values are evaluated in a list context. You may override
this with C<scalar> as shown above.

These constants do not directly interpolate into double-quotish
strings, although you may do so indirectly. (See L<perlref> for
details about how this works.)

    print "The value of PI is @{[ PI ]}.\n";

List constants are returned as lists, not as arrays.

    $homedir = USERINFO[7];		# WRONG
    $homedir = (USERINFO)[7];		# Right

The use of all caps for constant names is merely a convention,
although it is recommended in order to make constants stand out
and to help avoid collisions with other barewords, keywords, and
subroutine names. Constant names must begin with a letter or
underscore. Names beginning with a double underscore are reserved. Some
poor choices for names will generate warnings, if warnings are enabled at
compile time.

Constant symbols are package scoped (rather than block scoped, as
C<use strict> is). That is, you can refer to a constant from package
Other as C<Other::CONST>.

As with all C<use> directives, defining a constant happens at
compile time. Thus, it's probably not correct to put a constant
declaration inside of a conditional statement (like C<if ($foo)