File Coverage

blib/lib/Chatbot/Eliza.pm

Criterion	Covered	Total	%
statement	136	235	57.8
branch	36	88	40.9
condition	11	30	36.6
subroutine	11	15	73.3
pod	6	6	100.0
total	200	374	53.4

###################################################################

package Chatbot::Eliza;
$Chatbot::Eliza::VERSION = '1.07';
# Copyright (c) 1997-2003 John Nolan. All rights reserved.
# This program is free software.  You may modify and/or
# distribute it under the same terms as Perl itself.
# This copyright notice must remain attached to the file.
#
# You can run this file through either pod2man or pod2html
# to produce pretty documentation in manual or html file format
# (these utilities are part of the Perl 5 distribution).
#
# POD documentation is distributed throughout the actual code
# so that it also functions as comments.

require 5.006;
use strict;
use warnings;
use Carp;

our $AUTOLOAD;



####################################################################
# ---{ B E G I N   P O D   D O C U M E N T A T I O N }--------------
#

=head1  NAME

B - A clone of the classic Eliza program

=head1 SYNOPSIS

  use Chatbot::Eliza;

  $mybot = new Chatbot::Eliza;
  $mybot->command_interface;

  # see below for details


=head1 DESCRIPTION

This module implements the classic Eliza algorithm.
The original Eliza program was written by Joseph
Weizenbaum and described in the Communications
of the ACM in 1966.  Eliza is a mock Rogerian
psychotherapist.  It prompts for user input,
and uses a simple transformation algorithm
to change user input into a follow-up question.
The program is designed to give the appearance
of understanding.

This program is a faithful implementation of the program
described by Weizenbaum.  It uses a simplified script
language (devised by Charles Hayden).  The content
of the script is the same as Weizenbaum's.

This module encapsulates the Eliza algorithm
in the form of an object.  This should make
the functionality easy to incorporate in larger programs.


=head1 INSTALLATION

The current version of Chatbot::Eliza.pm is available on CPAN:

  http://www.perl.com/CPAN/modules/by-module/Chatbot/

To install this package, just change to the directory which
you created by untarring the package, and type the following:

	perl Makefile.PL
	make test
	make
	make install

This will copy Eliza.pm to your perl library directory for
use by all perl scripts.  You probably must be root to do this,
unless you have installed a personal copy of perl.


=head1 USAGE

This is all you need to do to launch a simple
Eliza session:

	use Chatbot::Eliza;

	$mybot = new Chatbot::Eliza;
	$mybot->command_interface;

You can also customize certain features of the
session:

	$myotherbot = new Chatbot::Eliza;

	$myotherbot->name( "Hortense" );
	$myotherbot->debug( 1 );

	$myotherbot->command_interface;

These lines set the name of the bot to be
"Hortense" and turn on the debugging output.

When creating an Eliza object, you can specify
a name and an alternative scriptfile:

	$bot = new Chatbot::Eliza "Brian", "myscript.txt";

You can also use an anonymous hash to set these parameters.
Any of the fields can be initialized using this syntax:

	$bot = new Chatbot::Eliza {
		name       => "Brian",
		scriptfile => "myscript.txt",
		debug      => 1,
		prompts_on => 1,
		memory_on  => 0,
		myrand     =>
			sub { my $N = defined $_[0] ? $_[0] : 1;  rand($N); },
	};

If you don't specify a script file, then the new object will be
initialized with a default script.  The module contains this
script within itself.

You can use any of the internal functions in
a calling program.  The code below takes an
arbitrary string and retrieves the reply from
the Eliza object:

	my $string = "I have too many problems.";
	my $reply  = $mybot->transform( $string );

You can easily create two bots, each with a different
script, and see how they interact:

	use Chatbot::Eliza

	my ($harry, $sally, $he_says, $she_says);

	$sally = new Chatbot::Eliza "Sally", "histext.txt";
	$harry = new Chatbot::Eliza "Harry", "hertext.txt";

	$he_says  = "I am sad.";

	# Seed the random number generator.
	srand( time ^ ($$ + ($$ << 15)) );

	while (1) {
		$she_says = $sally->transform( $he_says );
		print $sally->name, ": $she_says \n";

		$he_says  = $harry->transform( $she_says );
		print $harry->name, ": $he_says \n";
	}

Mechanically, this works well.  However, it critically depends
on the actual script data.  Having two mock Rogerian therapists
talk to each other usually does not produce any sensible conversation,
of course.

After each call to the transform() method, the debugging output
for that transformation is stored in a variable called $debug_text.

	my $reply      = $mybot->transform( "My foot hurts" );
	my $debugging  = $mybot->debug_text;

This feature always available, even if the instance's $debug
variable is set to 0.

Calling programs can specify their own random-number generators.
Use this syntax:

        $chatbot = new Chatbot::Eliza;
        $chatbot->myrand(
                sub {
                        #function goes here!
                }
        );

The custom random function should have the same prototype
as perl's built-in rand() function.  That is, it should take
a single (numeric) expression as a parameter, and it should
return a floating-point value between 0 and that number.

What this code actually does is pass a reference to an anonymous
subroutine ("code reference").  Make sure you've read the perlref
manpage for details on how code references actually work.

If you don't specify any custom rand function, then the Eliza
object will just use the built-in rand() function.

=head1 MAIN DATA MEMBERS

Each Eliza object uses the following data structures
to hold the script data in memory:

=head2 %decomplist

I: the set of keywords;  I: strings containing
the decomposition rules.

=head2 %reasmblist

I: a set of values which are each the join
of a keyword and a corresponding decomposition rule;
I: the set of possible reassembly statements
for that keyword and decomposition rule.

=head2 %reasmblist_for_memory

This structure is identical to C<%reasmblist>, except
that these rules are only invoked when a user comment
is being retrieved from memory. These contain comments
such as "Earlier you mentioned that...," which are only
appropriate for remembered comments.  Rules in the script
must be specially marked in order to be included
in this list rather than C<%reasmblist>. The default
script only has a few of these rules.

=head2 @memory

A list of user comments which an Eliza instance is remembering
for future use.  Eliza does not remember everything, only some things.
In this implementation, Eliza will only remember comments
which match a decomposition rule which actually has reassembly
rules that are marked with the keyword "reasm_for_memory"
rather than the normal "reasmb".  The default script
only has a few of these.

=head2 %keyranks

I: the set of keywords;  I: the ranks for each keyword

=head2 @quit

"quit" words -- that is, words the user might use
to try to exit the program.

=head2 @initial

Possible greetings for the beginning of the program.

=head2 @final

Possible farewells for the end of the program.

=head2 %pre

I: words which are replaced before any transformations;
I: the respective replacement words.

=head2 %post

I: words which are replaced after the transformations
and after the reply is constructed;  I: the respective
replacement words.

=head2 %synon

I: words which are found in decomposition rules;
I: words which are treated just like their
corresponding synonyms during matching of decomposition
rules.

=head2 Other data members

There are several other internal data members.  Hopefully
these are sufficiently obvious that you can learn about them
just by reading the source code.

=cut


my %fields = (
	name 		=> 'Eliza',
	scriptfile	=> '',

	debug 		=> 0,
	debug_text	=> '',
	transform_text	=> '',
	prompts_on	=> 1,
	memory_on       => 1,
	botprompt	=> '',
	userprompt	=> '',

	myrand          =>
			sub { my $N = defined $_[0] ? $_[0] : 1;  rand($N); },

	keyranks	=> undef,
	decomplist	=> undef,
	reasmblist	=> undef,
	reasmblist_for_memory	=> undef,

	pre		=> undef,
	post		=> undef,
	synon		=> undef,
	initial		=> undef,
	final		=> undef,
	quit		=> undef,

	max_memory_size			=> 5,
	likelihood_of_using_memory	=> 1,
	memory				=> undef,
);


####################################################################
# ---{ B E G I N   M E T H O D S }----------------------------------
#

=head1 METHODS

=head2 new()

    my $chatterbot = new Chatbot::Eliza;

new() creates a new Eliza object.  This method
also calls the internal _initialize() method, which in turn
calls the parse_script_data() method, which initializes
the script data.

    my $chatterbot = new Chatbot::Eliza 'Ahmad', 'myfile.txt';

The eliza object defaults to the name "Eliza", and it
contains default script data within itself.  However,
using the syntax above, you can specify an alternative
name and an alternative script file.

See the method parse_script_data(). for a description
of the format of the script file.

=cut

sub new {
	my ($that,$name,$scriptfile) = @_;
	my $class = ref($that) || $that;
	my $self = {
		_permitted => \%fields,
		%fields,
	};
	bless $self, $class;
	$self->_initialize($name,$scriptfile);
	return $self;
} # end method new

sub _initialize {
	my ($self,$param1,$param2) = @_;

	if (defined $param1 and ref $param1 eq "HASH") {

		# Allow the calling program to pass in intial parameters
		# as an anonymous hash
		map { $self->{$_} = $param1->{$_}; } keys %$param1;

		$self->parse_script_data( $self->{scriptfile} );

	} else {
		$self->name($param1) if $param1;
		$self->parse_script_data($param2);
	}

	# Initialize the memory array ref at instantiation time,
	# rather than at class definition time.
	# (THANKS to Randal Schwartz and Robert Chin for fixing this bug.)
	#
	$self->{memory} = [];
}

sub AUTOLOAD {
	my $self = shift;
	my $class = ref($self) || croak "$self is not an object : $!\n";
	my $field = $AUTOLOAD;
	$field =~ s/.*://; # Strip fully-qualified portion

	unless (exists $self->{"_permitted"}->{$field} ) {
		croak "Can't access `$field' field in object of class $class : $!\n";
	}

	if (@_) {
		return $self->{$field} = shift;
	} else {
		return $self->{$field};
	}
} # end method AUTOLOAD


####################################################################
# --- command_interface ---

=head2 command_interface()

    $chatterbot->command_interface;

command_interface() opens an interactive session with
the Eliza object, just like the original Eliza program.

If you want to design your own session format, then
you can write your own while loop and your own functions
for prompting for and reading user input, and use the
transform() method to generate Eliza's responses.
(I: you do not need to invoke preprocess()
and postprocess() directly, because these are invoked
from within the transform() method.)

But if you're lazy and you want to skip all that,
then just use command_interface().  It's all done for you.

During an interactive session invoked using command_interface(),
you can enter the word "debug" to toggle debug mode on and off.
You can also enter the keyword "memory" to invoke the _debug_memory()
method and print out the contents of the Eliza instance's memory.

=cut

sub command_interface {
	my $self = shift;
	my ($user_input, $previous_user_input, $reply);

	$user_input = "";

	$self->botprompt($self->name . ":\t");	# Eliza's prompt
	$self->userprompt("you:\t");     	# User's prompt

	# Seed the random number generator.
	srand( time() ^ ($$ + ($$ << 15)) );

	# Print the Eliza prompt
	print $self->botprompt if $self->prompts_on;

	# Print an initial greeting
	print "$self->{initial}->[ int &{$self->{myrand}}( scalar @{ $self->{initial} } ) ]\n";


	###################################################################
	# command loop.  This loop should go on forever,
	# until we explicity break out of it.
	#
	while (1) {

		print $self->userprompt if $self->prompts_on;

		$previous_user_input = $user_input;
		chomp( $user_input =  );


		# If the user wants to quit,
		# print out a farewell and quit.
		if ($self->_testquit($user_input) ) {
			$reply = "$self->{final}->[ int &{$self->{myrand}}( scalar @{$self->{final}} ) ]";
			print $self->botprompt if $self->prompts_on;
			print "$reply\n";
			last;
		}

		# If the user enters the word "debug",
		# then toggle on/off this Eliza's debug output.
		if ($user_input eq "debug") {
			$self->debug( ! $self->debug );
			$user_input = $previous_user_input;
		}

		# If the user enters the word "memory",
		# then use the _debug_memory method to dump out
		# the current contents of Eliza's memory
		if ($user_input eq "memory" or $user_input eq "debug memory") {
			print $self->_debug_memory();
			redo;
		}

		# If the user enters the word "debug that",
		# then dump out the debugging of the
		# most recent call to transform.
		if ($user_input eq "debug that") {
			print $self->debug_text();
			redo;
		}

		# Invoke the transform method
		# to generate a reply.
		$reply = $self->transform( $user_input );


		# Print out the debugging text if debugging is set to on.
		# This variable should have been set by the transform method.
		print $self->debug_text if $self->debug;

		# Print the actual reply
		print $self->botprompt if $self->prompts_on;
		print "$reply\n";

	} # End UI command loop.


} # End method command_interface


####################################################################
# --- preprocess ---

=head2 preprocess()

    $string = preprocess($string);

preprocess() applies simple substitution rules to the input string.
Mostly this is to catch varieties in spelling, misspellings,
contractions and the like.

preprocess() is called from within the transform() method.
It is applied to user-input text, BEFORE any processing,
and before a reassebly statement has been selected.

It uses the array C<%pre>, which is created
during the parse of the script.

=cut

sub preprocess {
	my ($self,$string) = @_;

	my ($i, @wordsout, @wordsin, $keyword);

	@wordsout = @wordsin = split / /, $string;

	WORD: for ($i = 0; $i < @wordsin; $i++) {
		foreach $keyword (keys %{ $self->{pre} }) {
			if ($wordsin[$i] =~ /\b$keyword\b/i ) {
				($wordsout[$i] = $wordsin[$i]) =~ s/$keyword/$self->{pre}->{$keyword}/ig;
				next WORD;
			}
		}
	}
	return join ' ', @wordsout;
}


####################################################################
# --- postprocess ---

=head2 postprocess()

    $string = postprocess($string);

postprocess() applies simple substitution rules to the
reassembly rule.  This is where all the "I"'s and "you"'s
are exchanged.  postprocess() is called from within the
transform() function.

It uses the array C<%post>, created
during the parse of the script.

=cut

sub postprocess {
	my ($self,$string) = @_;

	my ($i, @wordsout, @wordsin, $keyword);

	@wordsin = @wordsout = split (/ /, $string);

	WORD: for ($i = 0; $i < @wordsin; $i++) {
		foreach $keyword (keys %{ $self->{post} }) {
			if ($wordsin[$i] =~ /\b$keyword\b/i ) {
				($wordsout[$i] = $wordsin[$i]) =~ s/$keyword/$self->{post}->{$keyword}/ig;
				next WORD;
			}
		}
	}
	return join ' ', @wordsout;
}

####################################################################
# --- _testquit ---

=head2 _testquit()

     if ($self->_testquit($user_input) ) { ... }

_testquit() detects words like "bye" and "quit" and returns
true if it finds one of them as the first word in the sentence.

These words are listed in the script, under the keyword "quit".

=cut

sub _testquit {
	my ($self,$string) = @_;

	my ($quitword, @wordsin);

	foreach $quitword (@{ $self->{quit} }) {
		return 1 if ($string =~ /\b$quitword\b/i ) ;
	}
}


####################################################################
# --- _debug_memory ---

=head2 _debug_memory()

     $self->_debug_memory()

_debug_memory() is a special function which returns
the contents of Eliza's memory stack.


=cut

sub _debug_memory {

	my ($self) = @_;

	my $string = "\t";
	$string .= $#{ $self->memory } + 1;
	$string .= " item(s) in memory stack:\n";

	# [THANKS to Roy Stephan for helping me adjust this bit]
	#
	foreach (@{ $self->memory } ) {

		my $line = $_;
		$string .= sprintf "\t\t->$line\n" ;
	};

	return $string;
}

####################################################################
# --- transform ---

=head2 transform()

    $reply = $chatterbot->transform( $string, $use_memory );

transform() applies transformation rules to the user input
string.  It invokes preprocess(), does transformations,
then invokes postprocess().  It returns the tranformed
output string, called C<$reasmb>.

The algorithm embedded in the transform() method has three main parts:

=over

=item 1

Search the input string for a keyword.

=item 2

If we find a keyword, use the list of decomposition rules
for that keyword, and pattern-match the input string against
each rule.

=item 3

If the input string matches any of the decomposition rules,
then randomly select one of the reassembly rules for that
decomposition rule, and use it to construct the reply.

=back

transform() takes two parameters.  The first is the string we want
to transform.  The second is a flag which indicates where this sting
came from.  If the flag is set, then the string has been pulled
from memory, and we should use reassembly rules appropriate
for that.  If the flag is not set, then the string is the most
recent user input, and we can use the ordinary reassembly rules.

The memory flag is only set when the transform() function is called
recursively.  The mechanism for setting this parameter is
embedded in the transoform method itself.  If the flag is set
inappropriately, it is ignored.

=cut

sub transform{
	my ($self,$string,$use_memory) = @_;

	# Initialize the debugging text buffer.
	$self->debug_text('');

	$self->debug_text(sprintf "\t[Pulling string \"$string\" from memory.]\n")
		if $use_memory;

	my ($i, @string_parts, $string_part, $rank, $goto, $reasmb, $keyword,
		$decomp, $this_decomp, $reasmbkey, @these_reasmbs,
		@decomp_matches, $synonyms, $synonym_index);

	# Default to a really low rank.
	$rank   = -2;
	$reasmb = "";
	$goto   = "";

	# First run the string through the preprocessor.
	$string = $self->preprocess( $string );

	# Convert punctuation to periods.  We will assume that commas
	# and certain conjunctions separate distinct thoughts/sentences.
	$string =~ s/[?!,]/./g;
	$string =~ s/but/./g;   #   Yikes!  This is English-specific.

	# Split the string by periods into an array
	@string_parts = split /\./, $string ;

	# Examine each part of the input string in turn.
	STRING_PARTS: foreach $string_part (@string_parts) {

	# Run through the whole list of keywords.
	KEYWORD: foreach $keyword (keys %{ $self->{decomplist} }) {

		# Check to see if the input string contains a keyword
		# which outranks any we have found previously
		# (On first loop, rank is set to -2.)
		if ( ($string_part =~ /\b$keyword\b/i or $keyword eq $goto)
		     and
		     $rank < $self->{keyranks}->{$keyword}
		   )
		{
			# If we find one, then set $rank to equal
			# the rank of that keyword.
			$rank = $self->{keyranks}->{$keyword};

			$self->debug_text($self->debug_text . sprintf "\t$rank> $keyword");

			# Now let's check all the decomposition rules for that keyword.
			DECOMP: foreach $decomp (@{ $self->{decomplist}->{$keyword} }) {

				# Change '*' to '\b(.*)\b' in this decomposition rule,
				# so we can use it for regular expressions.  Later,
				# we will want to isolate individual matches to each wildcard.
				($this_decomp = $decomp) =~ s/\s*\*\s*/\\b\(\.\*\)\\b/g;

				# If this docomposition rule contains a word which begins with '@',
				# then the script also contained some synonyms for that word.
				# Find them all using %synon and generate a regular expression
				# containing all of them.
				if ($this_decomp =~ /\@/ ) {
					($synonym_index = $this_decomp) =~ s/.*\@(\w*).*/$1/i ;
					$synonyms = join ('|', @{ $self->{synon}->{$synonym_index} });
					$this_decomp =~ s/(.*)\@$synonym_index(.*)/$1($synonym_index\|$synonyms)$2/g;
				}

				$self->debug_text($self->debug_text .  sprintf "\n\t\t: $decomp");

				# Using the regular expression we just generated,
				# match against the input string.  Use empty "()"'s to
				# eliminate warnings about uninitialized variables.
				if ($string_part =~ /$this_decomp()()()()()()()()()()/i) {

					# If this decomp rule matched the string,
					# then create an array, so that we can refer to matches
					# to individual wildcards.  Use '0' as a placeholder
					# (we don't want to refer to any "zeroth" wildcard).
					@decomp_matches = ("0", $1, $2, $3, $4, $5, $6, $7, $8, $9);
					$self->debug_text($self->debug_text . sprintf " : @decomp_matches\n");

					# Using the keyword and the decomposition rule,
					# reconstruct a key for the list of reassamble rules.
					$reasmbkey = join ($;,$keyword,$decomp);

					# Get the list of possible reassembly rules for this key.
					#
					my $memory = (defined $use_memory and $#{ $self->{reasmblist_for_memory}->{$reasmbkey} } >= 0);

					# Pick out next reassembly rule.
					$reasmb = $self->_get_next_reasmb( $reasmbkey, $memory);

					$self->debug_text($self->debug_text . sprintf "\t\t-->  $reasmb\n");

					# If the reassembly rule we picked contains the word "goto",
					# then we start over with a new keyword.  Set $keyword to equal
					# that word, and start the whole loop over.
					if ($reasmb =~ m/^goto\s(\w*).*/i) {
						$self->debug_text($self->debug_text . sprintf "\$1 = $1\n");
						$goto = $keyword = $1;
						$rank = -2;
						redo KEYWORD;
					}

					# Otherwise, using the matches to wildcards which we stored above,
					# insert words from the input string back into the reassembly rule.
					# [THANKS to Gidon Wise for submitting a bugfix here]
					for ($i=1; $i <= $#decomp_matches; $i++) {
						$decomp_matches[$i] = $self->postprocess( $decomp_matches[$i] );
						$decomp_matches[$i] =~ s/([,;?!]|\.*)$//;
						$reasmb =~ s/\($i\)/$decomp_matches[$i]/g;
					}

					# Move on to the next keyword.  If no other keywords match,
					# then we'll end up actually using the $reasmb string
					# we just generated above.
					next KEYWORD ;

				}  # End if ($string_part =~ /$this_decomp/i)

				$self->debug_text($self->debug_text . sprintf "\n");

			} # End DECOMP: foreach $decomp (@{ $self->{decomplist}->{$keyword} })

		} # End if ( ($string_part =~ /\b$keyword\b/i or $keyword eq $goto)

	} # End KEYWORD: foreach $keyword (keys %{ $self->{decomplist})

	} # End STRING_PARTS: foreach $string_part (@string_parts) {

=head2 How memory is used

In the script, some reassembly rules are special.  They are marked with
the keyword "reasm_for_memory", rather than just "reasm".
Eliza "remembers" any comment when it matches a docomposition rule
for which there are any reassembly rules for memory.
An Eliza object remembers up to C<$max_memory_size> (default: 5)
user input strings.

If, during a subsequent run, the transform() method fails to find any
appropriate decomposition rule for a user's comment, and if there are
any comments inside the memory array, then Eliza may elect to ignore
the most recent comment and instead pull out one of the strings from memory.
In this case, the transform method is called recursively with the memory flag.

Honestly, I am not sure exactly how this memory functionality
was implemented in the original Eliza program.  Hopefully
this implementation is not too far from Weizenbaum's.

If you don't want to use the memory functionality at all,
then you can disable it:

	$mybot->memory_on(0);

You can also achieve the same effect by making sure
that the script data does not contain any reassembly rules
marked with the keyword "reasm_for_memory".  The default
script data only has 4 such items.

=cut

	if ($reasmb eq "") {

		# If all else fails, call this method recursively
		# and make sure that it has something to parse.
		# Use a string from memory if anything is available.
		#
		# $self-likelihood_of_using_memory should be some number
		# between 1 and 0;  it defaults to 1.
		#
		if (
			$#{ $self->memory } >= 0
			and
			&{$self->{myrand}}(1) >= 1 - $self->likelihood_of_using_memory
		) {

			$reasmb =  $self->transform( shift @{ $self->memory }, "use memory" );

		} else {
			$reasmb =  $self->transform("xnone");
		}

	} elsif ($self->memory_on) {

		# If memory is switched on, then we handle memory.

		# Now that we have successfully transformed this string,
		# push it onto the end of the memory stack... unless, of course,
		# that's where we got it from in the first place, or if the rank
		# is not the kind we remember.
		#
		if (
				$#{ $self->{reasmblist_for_memory}->{$reasmbkey} } >= 0
				and
				not defined $use_memory
		) {

			push  @{ $self->memory },$string ;
		}

		# Shift out the least-recent item from the bottom
		# of the memory stack if the stack exceeds the max size.
		shift @{ $self->memory } if $#{ $self->memory } >= $self->max_memory_size;

		$self->debug_text($self->debug_text
			. sprintf("\t%d item(s) in memory.\n", $#{ $self->memory } + 1 ) ) ;

	} # End if ($reasmb eq "")

	$reasmb =~ tr/ / /s;       # Eliminate any duplicate space characters.
	$reasmb =~ s/[ ][?]$/?/;   # Eliminate any spaces before the question mark.

	# Save the return string so that forgetful calling programs
	# can ask the bot what the last reply was.
	$self->transform_text($reasmb);

	return $reasmb ;
}

# _get_next_reasmb( $key, $memory_flag )
#
# Given a key to a reasmb list and a flag indicating whether the list should
# be pulled from a memory list or standard script list, returns the
# next reasmb in the list, wrapping back to the start if the last one
# is reached.
sub _get_next_reasmb {
	my ( $self, $reasmbkey, $memory ) = @_;

	my $for_memory = $memory ? '_for_memory' : '';
	my @these_reasmbs = @{ $self->{"reasmblist$for_memory"}->{$reasmbkey} };
	my $next_reasmb = $self->{"next_reasmblist$for_memory"}->{$reasmbkey}++;
	if ( $next_reasmb > scalar( @these_reasmbs ) ) {
		$next_reasmb = 1;
		$self->{"next_reasmblist$for_memory"}->{$reasmbkey} = 0;
	}

	return $these_reasmbs[$next_reasmb - 1];
}

####################################################################
# --- parse_script_data ---

=head2 parse_script_data()

    $self->parse_script_data;
    $self->parse_script_data( $script_file );

parse_script_data() is invoked from the _initialize() method,
which is called from the new() function.  However, you can also
call this method at any time against an already-instantiated
Eliza instance.  In that case, the new script data is I
to the old script data.  The old script data is not deleted.

You can pass a parameter to this function, which is the name of the
script file, and it will read in and parse that file.
If you do not pass any parameter to this method, then
it will read the data embedded at the end of the module as its
default script data.

If you pass the name of a script file to parse_script_data(),
and that file is not available for reading, then the module dies.


=head1 Format of the script file

This module includes a default script file within itself,
so it is not necessary to explicitly specify a script file
when instantiating an Eliza object.

Each line in the script file can specify a key,
a decomposition rule, or a reassembly rule.

  key: remember 5
    decomp: * i remember *
      reasmb: Do you often think of (2) ?
      reasmb: Does thinking of (2) bring anything else to mind ?
    decomp: * do you remember *
      reasmb: Did you think I would forget (2) ?
      reasmb: What about (2) ?
      reasmb: goto what
  pre: equivalent alike
  synon: belief feel think believe wish

The number after the key specifies the rank.
If a user's input contains the keyword, then
the transform() function will try to match
one of the decomposition rules for that keyword.
If one matches, then it will select one of
the reassembly rules at random.  The number
(2) here means "use whatever set of words
matched the second asterisk in the decomposition
rule."

If you specify a list of synonyms for a word,
the you should use a "@" when you use that
word in a decomposition rule:

  decomp: * i @belief i *
    reasmb: Do you really think so ?
    reasmb: But you are not sure you (3).

Otherwise, the script will never check to see
if there are any synonyms for that keyword.

Reassembly rules should be marked with I
rather than I when it is appropriate for use
when a user's comment has been extracted from memory.

  key: my 2
    decomp: * my *
      reasm_for_memory: Let's discuss further why your (2).
      reasm_for_memory: Earlier you said your (2).
      reasm_for_memory: But your (2).
      reasm_for_memory: Does that have anything to do with the fact that your (2) ?

=head1 How the script file is parsed

Each line in the script file contains an "entrytype"
(key, decomp, synon) and an "entry", separated by
a colon.  In turn, each "entry" can itself be
composed of a "key" and a "value", separated by
a space.  The parse_script_data() function
parses each line out, and splits the "entry" and
"entrytype" portion of each line into two variables,
C<$entry> and C<$entrytype>.

Next, it uses the string C<$entrytype> to determine
what sort of stuff to expect in the C<$entry> variable,
if anything, and parses it accordingly.  In some cases,
there is no second level of key-value pair, so the function
does not even bother to isolate or create C<$key> and C<$value>.

C<$key> is always a single word.  C<$value> can be null,
or one single word, or a string composed of several words,
or an array of words.

Based on all these entries and keys and values,
the function creates two giant hashes:
C<%decomplist>, which holds the decomposition rules for
each keyword, and C<%reasmblist>, which holds the
reassembly phrases for each decomposition rule.
It also creates C<%keyranks>, which holds the ranks for
each key.

Six other arrays are created: C<%reasm_for_memory, %pre, %post,
%synon, @initial,> and C<@final>.

=cut

sub parse_script_data {

	my ($self,$scriptfile) = @_;
	my @scriptlines;

	if ($scriptfile) {

		# If we have an external script file, open it
		# and read it in (the whole thing, all at once).
		open  (SCRIPTFILE, "<$scriptfile")
			or die "Could not read from file $scriptfile : $!\n";
		@scriptlines = ; # read in script data
		$self->scriptfile($scriptfile);
		close (SCRIPTFILE);

	} else {

		# Otherwise, read in the data from the bottom
		# of this file.  This data might be read several
		# times, so we save the offset pointer and
		# reset it when we're done.
		my $where= tell(DATA);
		@scriptlines = ;  # read in script data
		seek(DATA, $where, 0);
		$self->scriptfile('');
	}

	my ($entrytype, $entry, $key, $value) ;
	my $thiskey    = "";
	my $thisdecomp = "";

	############################################################
	# Examine each line of script data.
	for (@scriptlines) {

		# Skip comments and lines with only whitespace.
		next if (/^\s*#/ || /^\s*$/);

		# Split entrytype and entry, using a colon as the delimiter.
		($entrytype, $entry) = $_ =~ m/^\s*(\S*)\s*:\s*(.*)\s*$/;

		# Case loop, based on the entrytype.
		for ($entrytype) {

			/quit/		and do { push @{ $self->{quit}    }, $entry; last; };
			/initial/	and do { push @{ $self->{initial} }, $entry; last; };
			/final/		and do { push @{ $self->{final}   }, $entry; last; };

			/decomp/	and do {
						die "$0: error parsing script:  decomposition rule with no keyword.\n"
							if $thiskey eq "";
						$thisdecomp = join($;,$thiskey,$entry);
						push @{ $self->{decomplist}->{$thiskey} }, $entry ;
						last;
					};

			/reasmb/	and do {
						die "$0: error parsing script:  reassembly rule with no decomposition rule.\n"
							if $thisdecomp eq "";
						push @{ $self->{reasmblist}->{$thisdecomp} }, $entry ;
						last;
					};

			/reasm_for_memory/	and do {
						die "$0: error parsing script:  reassembly rule with no decomposition rule.\n"
							if $thisdecomp eq "";
						push @{ $self->{reasmblist_for_memory}->{$thisdecomp} }, $entry ;
						last;
					};

			# The entrytypes below actually expect to see a key and value
			# pair in the entry, so we split them out.  The first word,
			# separated by a space, is the key, and everything else is
			# an array of values.

			($key,$value) = $entry =~ m/^\s*(\S*)\s*(.*)/;

			/pre/		and do { $self->{pre}->{$key}   = $value; last; };
			/post/		and do { $self->{post}->{$key}  = $value; last; };

			# synon expects an array, so we split $value into an array, using " " as delimiter.
			/synon/		and do { $self->{synon}->{$key} = [ split /\ /, $value ]; last; };

			/key/		and do {
						$thiskey = $key;
						$thisdecomp = "";
						$self->{keyranks}->{$thiskey} = $value ;
						last;
					};

		}  # End for ($entrytype) (case loop)

	}  # End for (@scriptlines)

}  # End of method parse_script_data


# Eliminate some pesky warnings.
#
sub DESTROY {}


# ---{ E N D   M E T H O D S }----------------------------------
####################################################################

1;  	# Return a true value.


=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2003 by John Nolan  [e-mail].

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=head1 AUTHOR

John Nolan  [e-mail]  January 2003.

Implements the classic Eliza algorithm by Prof. Joseph Weizenbaum.
Script format devised by Charles Hayden.

=cut



####################################################################
# ---{ B E G I N   D E F A U L T   S C R I P T   D A T A }----------
#
#  This script was prepared by Chris Hayden.  Hayden's Eliza
#  program was written in Java, however, it attempted to match
#  the functionality of Weizenbaum's original program as closely
#  as possible.
#
#  Hayden's script format was quite different from Weizenbaum's,
#  but it maintained the same content.  I have adapted Hayden's
#  script format, since it was simple and convenient enough
#  for my purposes.
#
#  I've made small modifications here and there.
#

# We use the token __DATA__ rather than __END__,
# so that all this data is visible within the current package.

__DATA__