This directory contains the source files for SHRDLU, a program
 written by Terry Winograd at the MIT AI Lab in 1968-1970.  For
 a full description, see Terry Winograd, Understanding Natural
 Language, Academic Press, 1972.

The version here is a cleaned up version done by Stu Card,
 Andee Rubin, and Terry Winograd in 1972.   The files are
 available for anyone who wants to use them (let me know
if you get something running!).

Terry Winograd (winograd@cs.stanford.edu)

--------

Excerpt from the  PROVISIONAL SHRDLU USERS' MANUAL (see file shrdlu/manual):

BRIEF DESCRIPTION OF SHRDLU
---------------------------

         SHRDLU IS A SYSTEM FOR THE  COMPUTER  UNDERSTANDING
    OF  ENGLISH.    THE  SYSTEM  ANSWERS QUESTIONS, EXECUTES
    COMMANDS, AND  ACCEPTS  INFORMATION  IN  NORMAL  ENGLISH
    DIALOG.    IT  USES  SEMANTIC INFORMATION AND CONTEXT TO
    UNDERSTAND DISCOURSE AND TO DISAMBIGUATE SENTENCES.   IT
    COMBINES  A COMPLETE SYNTACTIC ANALYSIS OF EACH SENTENCE
    WITH A "HEURISTIC  UNDERSTANDER"  WHICH  USES  DIFFERENT
    KINDS  OF  INFORMATION  ABOUT A SENTENCE, OTHER PARTS OF
    THE DISCOURSE, AND GENERAL INFORMATION ABOUT  THE  WORLD
    IN DECIDING WHAT THE SENTENCE MEANS.

         SHRDLU  IS  BASED  ON  THE  BELIEF  THAT A COMPUTER
    CANNOT DEAL  REASONABLY  WITH  LANGUAGE  UNLESS  IT  CAN
    "UNDERSTAND"  THE  SUBJECT IT IS DISCUSSING. THE PROGRAM
    IS GIVEN A DETAILED MODEL OF THE KNOWLEDGE NEEDED  BY  A
    SIMPLE  ROBOT  HAVING  ONLY A HAND AND AN EYE.  THE USER
    CAN GIVE IT  INSTRUCTIONS  TO  MANIPULATE  TOY  OBJECTS,
    INTERROGATE  IT ABOUT THE SCENE, AND GIVE IT INFORMATION
    IT WILL USE IN DEDUCTION.  IN ADDITION  TO  KNOWING  THE
    PROPERTIES  OF  TOY  OBJECTS,  THE  PROGRAM HAS A SIMPLE
    MODEL OF  ITS  OWN  MENTALITY.    IT  CAN  REMEMBER  AND
    DISCUSS ITS PLANS AND ACTIONS AS WELL AS CARRY THEM OUT.
    IT ENTERS INTO A DIALOG WITH  A  PERSON,  RESPONDING  TO
    ENGLISH  SENTENCES WITH ACTIONS AND ENGLISH REPLIES, AND
    ASKING FOR CLARIFICATION  WHEN  ITS  HEURISTIC  PROGRAMS
    CANNOT  UNDERSTAND A SENTENCE THROUGH USE OF CONTEXT AND
    PHYSICAL KNOWLEDGE.

         IN THE PROGRAMS, SYNTAX, SEMANTICS,  AND  INFERENCE
    ARE INTEGRATED IN A "VERTICAL" SYSTEM IN WHICH EACH PART
    IS CONSTANTLY COMMUNICATING WITH THE OTHERS. SHRDLU USES
    SYSTEMIC  GRAMMAR, A TYPE OF SYNTACTIC ANALYSIS WHICH IS
    DESIGNED  TO  DEAL  WITH   SEMANTICS.      RATHER   THAN
    CONCENTRATING  ON  THE EXACT FORM OF RULES FOR THE SHAPE
    OF LINGUISTIC  CONSTITUENTS,  IT  IS  STRUCTURED  AROUND
    CHOICES   FOR  CONVEYING  MEANING.    IT  ABSTRACTS  THE
    RELEVANT FEATURES OF THE LINGUISTIC STRUCTURES WHICH ARE
    IMPORTANT FOR INTERPRETING THEIR MEANING.

         IN  SHRDLU  MANY KINDS OF KNOWLEDGE ARE REPRESENTED
    IN THE FORM OF PROCEDURES RATHER THAN TABLES OF RULES OR
    LISTS  OF  PATTERNS.    BY DEVELOPING SPECIAL PROCEDURAL
    LANGUAGES FOR GRAMMAR, SEMANTICS, AND  DEDUCTIVE  LOGIC,
    THE  FLEXIBILITY  AND  POWER OF PROGRAMMING LANGUAGES IS
    GAINED    WHILE    RETAINING    THE    REGULARITY    AND
    UNDERSTANDABILITY  OF SIMPLER RULE FORMS.  EACH PIECE OF
    KNOWLEDGE CAN BE A PROCEDURE, AND CAN CALL ON ANY  OTHER
    PIECE OF KNOWLEDGE IN THE SYSTEM.

IMPLEMENTATION AND VERSION INFORMATION
--------------------------------------

        SHRDLU  WAS  PROGRAMMED  AT   THE   MIT   ARTIFICIAL
    INTELLIGENCE  LABORATORY  BY  T.   WINOGRAD AS PART OF A
    DOCTORAL DISSERTATION IN MATHEMATICS.

        THE PROGRAM WAS MODIFIED DURING THE LAST YEAR BY  T.
    WINOGRAD,  D.  MACDONALD, J. HILL, AND S. CARD TO CHANGE
    SOME OF ITS INTERNAL REPRESENTATIONS  AND  TO  MAKE  THE
    CODE  EASIER  TO UNDERSTAND FOR PERSONS WISHING TO STUDY
    THE PROGRAM.  NO MAJOR ATTEMPTS WERE  MADE  TO  INCREASE
    ITS POWER.

        THE PROGRAM RUNNING AT C-MU IS THE MODIFIED VERSION.
    THE DISPLAY FACILITIES OF  THE  PROGRAM  HAVE  NOT  BEEN
    IMPLEMENTED  AT  C-MU.  THE PROGRAM WAS COAXED AWAY FROM
    MIT'S  INCOMPATIBLE  TIME-SHARING   SYSTEM   (ITS)   AND
    CONVERTED  TO RUN UNDER THE DEC TOPS10 (10-50) OPERATING
    SYSTEM BY CONVERTING MACLISP ITSELF  (AND  TO  DO  THAT,
    CONVERTING  THE  MIDAS  ASSEMBLY LANGUAGE).  THE MACLISP
    CONVERSION WAS DONE BY GEORGE ROBERTSON.

THE VERSION OF SHRDLU BEING DISTRIBUTED FROM  CMU  IS  NAMED
    THE  C1  VERSION.  IT IS CURRENT WITH THE MIT VERSION TO
    JUNE 1972.  THE SHOW AND TELL USER INTERFACE AND VARIOUS
    CHANGES   WERE  ADDED  FOR  THE  C-MU  WORKSHOP  ON  NEW
    TECHNOLOGIES IN COGNITIVE RESEARCH IN JUNE 1972.

        SHRDLU IS  WRITTEN  IN  MACLISP  1.6  (VINTAGE  JUNE
    1972).  IT USES ABOUT 100 TO 140K 36-BIT WORDS OF MEMORY
    ON A PDP-10.