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=encoding utf8
=head1 NAME
Math::Symbolic::Constant - Constants in symbolic calculations
=head1 SYNOPSIS
  use Math::Symbolic::Constant;
  my $const = Math::Symbolic::Constant->new(25);
  my $zero  = Math::Symbolic::Constant->zero();
  my $one   = Math::Symbolic::Constant->one();
  my $euler = Math::Symbolic::Constant->euler();
  # e = 2.718281828...
=head1 DESCRIPTION
This module implements numeric constants for Math::Symbolic trees.
=head2 EXPORT
None by default.
=cut
package Math::Symbolic::Constant;
use 5.006;
use strict;
use warnings;
use Carp;
use Math::Symbolic::ExportConstants qw/:all/;
use base 'Math::Symbolic::Base';
our $VERSION = '0.613';
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=head1 METHODS
=cut
=head2 Constructor new
Takes hash reference of key-value pairs as argument.
Special case: a value for the constant instead of the hash.
Returns a Math::Symbolic::Constant.
=cut
sub new {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    my %args;
    %args = %{ shift() } if @_ && ref( $_[0] ) eq 'HASH';
    my $value = ( @_ && !%args ? shift : $args{value} );
    $value = $proto->value() if !defined($value) and ref($proto);
    croak("Math::Symbolic::Constant created with undefined value!")
      if not defined($value);
    my $self = {
        special => '',
        ( ref($proto) ? %$proto : () ),
        value => $value,
        %args,
    };
    bless $self => $class;
}
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=head2 Constructor zero
Arguments are treated as key-value pairs of object attributes.
Returns a Math::Symbolic::Constant with value of 0.
=cut
sub zero {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    croak("Uneven number of arguments to zero()") if @_ % 2;
    return(
            bless {@_, value => 0, special => 'zero' } => $class
        );
#    return $class->new( { @_, value => 0, special => 'zero' } );
}
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=head2 Constructor one
Arguments are treated as key-value pairs of object attributes.
Returns a Math::Symbolic::Constant with value of 1.
=cut
sub one {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    croak("Uneven number of arguments to one()") if @_ % 2;
    return(
            bless {@_, value => 1, special => 'one' } => $class
        );
         
    #return $class->new( { @_, value => 1 } );
}
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=head2 Constructor euler
Arguments are treated as key-value pairs of object attributes.
Returns a Math::Symbolic::Constant with value of e, the Euler number.
The object has its 'special' attribute set to 'euler'.
=cut
sub euler {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    croak("Uneven number of arguments to euler()") if @_ % 2;
    return(
            bless {@_, value => EULER, special => 'euler' } => $class
        );
     
        #return $class->new( { @_, value => EULER, special => 'euler' } );
}
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=head2 Constructor pi
Arguments are treated as key-value pairs of object attributes.
Returns a Math::Symbolic::Constant with value of pi.
The object has its 'special' attribute set to 'pi'.
=cut
sub pi {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    croak("Uneven number of arguments to pi()") if @_ % 2;
    return(
            bless {@_, value => PI, special => 'pi' } => $class
        );
     
        #return $class->new( { @_, value => PI, special => 'pi' } );
}
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=head2 Method value
value() evaluates the Math::Symbolic tree to its numeric representation.
value() without arguments requires that every variable in the tree contains
a defined value attribute. Please note that this refers to every variable
I<object>, not just every named variable.
value() with one argument sets the object's value if you're dealing with
Variables or Constants. In case of operators, a call with one argument will
assume that the argument is a hash reference. (see next paragraph)
value() with named arguments (key/value pairs) associates variables in the tree
with the value-arguments if the corresponging key matches the variable name.
(Can one say this any more complicated?) Since version 0.132, an
equivalent and valid syntax is to pass a single hash reference instead of a
list.
Example: $tree->value(x => 1, y => 2, z => 3, t => 0) assigns the value 1 to
any occurrances of variables of the name "x", aso.
If a variable in the tree has no value set (and no argument of value sets
it temporarily), the call to value() returns undef.
=cut
sub value {
    my $self = shift;
    if ( @_ == 1 and not ref( $_[0] ) eq 'HASH' ) {
        croak "Constant assigned undefined value!"
          if not defined $_[0];
         
                $self->{value}   = $_[0];
        $self->{special} = undef;    # !!!FIXME!!! one day, this
                                     # needs better handling.
    }
    return $self->{value};
}
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=head2 Method signature
signature() returns a tree's signature.
In the context of Math::Symbolic, signatures are the list of variables
any given tree depends on. That means the tree "v*t+x" depends on the
variables v, t, and x. Thus, applying signature() on the tree that would
be parsed from above example yields the sorted list ('t', 'v', 'x').
Constants do not depend on any variables and therefore return the empty list.
Obviously, operators' dependencies vary.
Math::Symbolic::Variable objects, however, may have a slightly more
involved signature. By convention, Math::Symbolic variables depend on
themselves. That means their signature contains their own name. But they
can also depend on various other variables because variables themselves
can be viewed as placeholders for more compicated terms. For example
in mechanics, the acceleration of a particle depends on its mass and
the sum of all forces acting on it. So the variable 'acceleration' would
have the signature ('acceleration', 'force1', 'force2',..., 'mass', 'time').
If you're just looking for a list of the names of all variables in the tree,
you should use the explicit_signature() method instead.
=cut
sub signature {
    return ();
}
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=head2 Method explicit_signature
explicit_signature() returns a lexicographically sorted list of
variable names in the tree.
See also: signature().
=cut
sub explicit_signature {
    return ();
}
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=head2 Method special
Optional argument: sets the object's special attribute.
Returns the object's special attribute.
=cut
sub special {
    my $self = shift;
    $self->{special} = shift if @_;
    return $self->{special};
}
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=head2 Method to_string
Returns a string representation of the constant.
=cut
sub to_string {
    my $self = shift;
    return $self->value();
}
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=head2 Method term_type
Returns the type of the term. (T_CONSTANT)
=cut
sub term_type { T_CONSTANT }
1;
__END__
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=head1 AUTHOR
Please send feedback, bug reports, and support requests to the Math::Symbolic
support mailing list:
math-symbolic-support at lists dot sourceforge dot net. Please
consider letting us know how you use Math::Symbolic. Thank you.
If you're interested in helping with the development or extending the
module's functionality, please contact the developers' mailing list:
math-symbolic-develop at lists dot sourceforge dot net.
List of contributors:
  Steffen Müller, symbolic-module at steffen-mueller dot net
  Stray Toaster, mwk at users dot sourceforge dot net
  Oliver Ebenhöh
=head1 SEE ALSO
New versions of this module can be found on
http://steffen-mueller.net or CPAN. The module development takes place on
Sourceforge at http://sourceforge.net/projects/math-symbolic/
L<Math::Symbolic>
=cut