Language::Prolog::Types::overload - nice formating for Prolog terms.

Language-Prolog-Types documentation Contained in the Language-Prolog-Types distribution.

Index

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NAME

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Language::Prolog::Types::overload - nice formating for Prolog terms.

SYNOPSIS

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use Language::Prolog::Types::overload;

ABSTRACT

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This module activates overloading features for Prolog terms.

DESCRIPTION

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When this module is loaded, Prolog terms are automatically converted to strings when printed or concatenated.

When used in bool context, all terms but variables return true, even the nil term.

In numerical context, functors return its arity and lists its length.

EXPORT

None by default.

SEE ALSO

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Language::Prolog::Types and Language::Prolog::Types::Abstract

AUTHOR

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Salvador Fandiņo, <sfandino@yahoo.com>

COPYRIGHT AND LICENSE

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Copyright 2002 by Salvador Fandiņo

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Language-Prolog-Types documentation Contained in the Language-Prolog-Types distribution. 
package Language::Prolog::Types::overload;

our $VERSION = '0.01';

use strict;
use warnings;

use Language::Prolog::Types;

package Language::Prolog::Types::Nil;
use overload
    '""' => sub {'[]'},
    '0+' => sub { 0 },
    'bool' => sub { 1 },
    'fallback' => 1;


package Language::Prolog::Types::Variable;
use overload
    '""' => sub {
	my $name=$_[0]->name;
	sprintf(($name=~/^[A-Z_]/ ? '%s' : '_%s') , $name)
    },
    '0+'=> sub { undef },
    'bool' => sub { 0 },
    'fallback' => 1 ;


package Language::Prolog::Types::Functor;

sub _escape($) {
    my $n=shift;
    return $n if $n=~/^[a-z][A-Za-z0-9_]*$/;
    return "'$n'"
}

use overload
    '""' => sub {
	my $self=shift;
	_escape($self->functor()).'(' . join(", ", $self->fargs) . ')'
    },
    '0+' => sub { $_[0]->arity },
    'bool' => sub { 1 },
    'fallback' => 1 ;


package Language::Prolog::Types::List;
use overload
    '""' => sub { '['.join(", ", $_[0]->largs()).']'},
    '0+' => sub { $_[0]->length },
    'bool' => sub { 1 },
    'fallback' => 1 ;


package Language::Prolog::Types::UList;
use overload
    '""' => sub {
	my $self=shift;
	'['.
	    join(', ', ($self->largs()))
		.' | '.
		    $self->tail.
			']'
    },
    "0+" => sub { $_[0]->length },
    'bool' => sub { 1 },
    'fallback' => 1;


package Language::XSB::Type::Unknow;
use overload
    '""' => sub { "<prolog_unknow ".$_[0]->id.">" },
    '0+' => sub { 0 },
    'bool' => sub { 1 },
    'fallback' => 1;


1;
__END__