TUTOR, also known as PLATO Author Language, is a programming language developed for use on the PLATO system at the University of Illinois at Urbana-Champaign beginning in roughly 1965. TUTOR was initially designed by Paul Tenczar for use in computer assisted instruction (CAI) and computer managed instruction (CMI) (in computer programs called "lessons") and has many features for that purpose. For example, TUTOR has powerful answer-parsing and answer-judging commands, graphics, and features to simplify handling student records and statistics by instructors. TUTOR's flexibility, in combination with PLATO's computational power (running on what was considered a supercomputer in 1972), also made it suitable for the creation of games — including flight simulators, war games, dungeon style multiplayer role-playing games, card games, word games, and medical lesson games such as Bugs and Drugs (BND). TUTOR lives on today as the programming language for the Cyber1 PLATO System, which runs most of the source code from 1980s PLATO and has roughly 5000 users as of June 2020.
Origins and development
TUTOR was originally developed as a special purpose authoring language for designing instructional lessons, and its evolution into a general purpose programming language was unplanned. The name TUTOR was first applied to the authoring language of the PLATO system in the later days of Plato III. The first documentation of the language, under this name, appears to have been The TUTOR Manual, CERL Report X-4, by R. A. Avner and P. Tenczar, Jan. 1969.
The article Teaching the Translation of Russian by Computer gives a snapshot of TUTOR from shortly before PLATO IV was operational. Core elements of the language were present, but commands were given in upper case, and instead of using a general mechanism, support for alternative character sets was through special command names such as WRUSS for "write using the Russian character set."
Through the 1970s, the developers of TUTOR took advantage of the fact that the entire corpus of TUTOR programs were stored on-line on the same computer system. Whenever they felt a need to change the language, they ran conversion software over the corpus of TUTOR code to revise all existing code so that it conformed with the changes they had made. As a result, once new versions of TUTOR were developed, maintaining compatibility with the PLATO version could be very difficult.
Control Data Corporation (CDC), by 1981, had largely expunged the name TUTOR from their PLATO documentation. They referred to the language itself as the PLATO Author Language. The phrase TUTOR file or even TUTOR lesson file survived, however, as the name of the type of file used to store text written in the PLATO Author Language.
Structure of a TUTOR lesson
A TUTOR lesson consists of a sequence of units where each unit begins with the presentation of information and progress from one unit to the next is contingent on correctly answering one or more questions. As with COBOL paragraphs, control may enter a TUTOR unit from the preceding unit and exit into the next, but units are also callable as subroutines using the do or join commands.
Here is an example unit from page 5 of the TUTOR User's Memo, March 1973 (Computer-based Education Research Laboratory, University of Illinois at Urbana-Champaign):
unit math
at 205
write Answer these problems
3 + 3 =
4 × 3 =
arrow 413
answer 6
arrow 613
answer 12
Several things should be immediately apparent from this example.
First, TUTOR is a fixed format language. Each line begins with a command name, which must fit within a fixed 8-character field for the command name. The arguments to that command (the tag) begin at the 9th character. Although a tab key was be used to get to the 9th column, it generated spaces as plato had no tab character. In some cases, such as the write command above, the tag may consist of multiple lines. Continuation lines are either blank or have a leading tab. Screen coordinates are presented as single numbers, so 205 refers to line 2 column 5, and 413 refers to line 4 column 13.
What may not be apparent is the control structure implicit in this unit. The arrow command marks the entrance to a judging block This control structure is one of TUTOR's unique features.
Unique features
TUTOR contained a number of unique features. The following list is not intended as a substitute for a TUTOR manual, but merely highlights the most interesting, innovative, and sometimes confusing features of the language.