Chatbot::Eliza(3) User Contributed Perl Documentation Chatbot::Eliza(3)NAMEChatbot::Eliza - A clone of the classic Eliza program
SYNOPSIS
use Chatbot::Eliza;
$mybot = new Chatbot::Eliza;
$mybot->command_interface;
# see below for details
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.
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.
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.
MAIN DATA MEMBERS
Each Eliza object uses the following data structures to hold the script
data in memory:
%decomplist
Hash: the set of keywords; Values: strings containing the
decomposition rules.
%reasmblist
Hash: a set of values which are each the join of a keyword and a
corresponding decomposition rule; Values: the set of possible
reassembly statements for that keyword and decomposition rule.
%reasmblist_for_memory
This structure is identical to %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
%reasmblist. The default script only has a few of these rules.
@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.
%keyranks
Hash: the set of keywords; Values: the ranks for each keyword
@quit
"quit" words -- that is, words the user might use to try to exit the
program.
@initial
Possible greetings for the beginning of the program.
@final
Possible farewells for the end of the program.
%pre
Hash: words which are replaced before any transformations; Values: the
respective replacement words.
%post
Hash: words which are replaced after the transformations and after the
reply is constructed; Values: the respective replacement words.
%synon
Hash: words which are found in decomposition rules; Values: words which
are treated just like their corresponding synonyms during matching of
decomposition rules.
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.
METHODSnew()
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.
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. (Note: 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.
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 %pre, which is created during the parse of the
script.
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 %post, created during the parse of the script.
_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".
_debug_memory()
$self->_debug_memory()_debug_memory() is a special function which returns the contents of
Eliza's memory stack.
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 $reasmb.
The algorithm embedded in the transform() method has three main parts:
1. Search the input string for a keyword.
2. If we find a keyword, use the list of decomposition rules for that
keyword, and pattern-match the input string against each rule.
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.
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.
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 $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.
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 added 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.
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 reasm_for_memory rather than
reasmb 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) ?
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, $entry
and $entrytype.
Next, it uses the string $entrytype to determine what sort of stuff to
expect in the $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 $key and $value.
$key is always a single word. $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: %decomplist, which holds the decomposition rules for
each keyword, and %reasmblist, which holds the reassembly phrases for
each decomposition rule. It also creates %keyranks, which holds the
ranks for each key.
Six other arrays are created: "%reasm_for_memory, %pre, %post, %synon,
@initial," and @final.
CHANGES
· Version 1.02-1.04 - January 2003
Added a Norwegian script, kindly contributed by
Mats Stafseng Einarsen. Thanks Mats!
· Version 1.01 - January 2003
Added an empty DESTORY method, to eliminate
some pesky warning messages. Suggested by
Stas Bekman.
· Version 0.98 - March 2000
Some changes to the documentation.
· Versions 0.96-0.97 - October 1999
One tiny change to the regex which implements
reassemble rules. Thanks to Gidon Wise for
suggesting this improvement.
· Versions 0.94-0.95 - July 1999
Fixed a bug in the way the bot invokes its random function
when it pulls a comment out of memory.
· Version 0.93 - June 1999
Calling programs can now 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.
You can also now use a reference to an anonymous hash
as a parameter to the new() method to define any fields
in that bot instance:
$bot = new Chatbot::Eliza {
name => "Brian",
scriptfile => "myscript.txt",
debug => 1,
};
· Versions 0.91-0.92 - April 1999
Fixed some misspellings.
· Version 0.90 - April 1999
Fixed a bug in the way individual bot objects store
their memory. Thanks to Randal Schwartz and to
Robert Chin for pointing this out.
Fixed a very stupid error in the way the random
function is invoked. Thanks to Antony Quintal
for pointing out the error.
Many corrections and improvements were made
to the German script by Matthias Hellmund.
Thanks, Matthias!
Made a minor syntactical change, at the suggestion
of Roy Stephan.
The memory functionality can now be disabled by setting the
$Chatbot::Eliza::memory_on variable to 0, like so:
$bot->memory_on(0);
Thanks to Robert Chin for suggesting that.
· Version 0.40 - July 1998
Re-implemented the memory functionality.
Cleaned up and expanded the embedded POD documentation.
Added a sample script in German.
Modified the debugging behavior. The transform() method itself
will no longer print any debugging output directly to STDOUT.
Instead, all debugging output is stored in a module variable
called "debug_text". The "debug_text" variable is printed out
by the command_interface() method, if the debug flag is set.
But even if this flag is not set, the variable debug_text
is still available to any calling program.
Added a few more example scripts which use the module.
simple - simple script using Eliza.pm
simple.cgi - simple CGI script using Eliza.pm
debug.cgi - CGI script which displays debugging output
deutsch - script using the German script
deutsch.cgi - CGI script using the German script
twobots - script which creates two distinct bots
· Version 0.32 - December 1997
Fixed a bug in the way Eliza loads its default internal script data.
(Thanks to Randal Schwartz for pointing this out.)
Removed the "memory" functions internal to Eliza.
When I get them working properly I will add them back in.
Added one more example program.
Fixed some minor errors in the embedded POD documentation.
· Version 0.31
The module is now installable, just like any other self-respecting
CPAN module.
· Version 0.30
First release.
AUTHOR
John Nolan jpnolan@sonic.net January 2003.
Implements the classic Eliza algorithm by Prof. Joseph Weizenbaum.
Script format devised by Charles Hayden.
perl v5.14.0 2003-01-24 Chatbot::Eliza(3)
