VIOLET

VIOLET (Verbose Interactive Operating Language for Educational Terminals) is an interpreted programming language alleged to have been the custom onboard language developed for a 1980s educational computer, the Buttech CAI-1.

An interpreter for VIOLET written in Python is included as part of the BlueBox library, itself a graphics library for producing a basic retro terminal interface.

History

According to the VIOLET and BlueBox documentation, VIOLET was created by a community college intern in a matter of days as a hasty replacement for rejected BASIC and PILOT proposals, and cobbled together from bits of other languages from FORTH to LISP.

Basic Operation

All VIOLET programs are composed of operator statements, which take arguments, and return their values to a built in value named &LAST. Each line can only contain one operator, save for the IFY/IFN operators, which may call a sub operator if they are successful. Variables are strictly typed, and their values can only be changed by the SET operator. Flow control is in the form of an IF/IFY/IFN operator set similar to PILOT C:/CY:/CN:, as well as a WHILE/WHEND loop, and the dreaded GOTO statement, here particularly problematic because line numbers aren't hard set but based on file position.

Because the VIOLET interactive editor can also handle arbitrary text files, the interpreter first checks any file sent to it for a PROGRAM START clause at the beginning, and a PROGRAM STOP clause at the end.

Sample Code

Taken from the included samples in the repository:

PROGRAM START
IGNORE  HELLO WORLD
IGNORE
PROMPT $ "WHAT IS YOUR NAME: "
SET $NAME &LAST
ADD "HELLO " $NAME "."
PRINT &LAST
PROGRAM STOP

PROGRAM START
IGNORE  EXPONENT CALCULATOR
IGNORE
PRINT EXPONENT CALCULATOR
PRINT PLEASE USE WHOLE NUMBERS ONLY
PROMPT # "BASE: "
SET #BASE &LAST
PROMPT # "EXPONENT: "
SET #EXP &LAST
SET #TOTAL 1
SET #X 0
WHILE LESSER #X #EXP
MULT #TOTAL #BASE
SET #TOTAL &LAST
ADD #X 1
SET #X &LAST
WHEND
PRINT "YOUR TOTAL IS: " #TOTAL
PROGRAM STOP

PROGRAM START
IGNORE  FACTORIAL SOLVER
IGNORE
PRINT "FACTORIAL SOLVER"
PRINT "PLEASE USE WHOLE NUMBERS"
SET #RUN 1
WHILE EQUALS #RUN 1
PROMPT # "ENTER NUMBER: "
SET #X &LAST
SET #Y #X
SET #TOTAL 1
WHILE GREATER #Y 0
MULT #TOTAL #Y
SET #TOTAL &LAST
SUB #Y 1
SET #Y &LAST
WHEND
PRINT #X "! = " #TOTAL
PROMPT $ "RUN AGAIN? "
IF EQUALS &LAST "YES"
IFY SET #RUN 1
IFN SET #RUN 0
WHEND
PROGRAM STOP

External resources

• BlueBox - A graphics library for simulating the appearance of CAI-1 applications. Includes violet.py, a VIOLET interpreter in Python 2.7.
• The VIOLET Programming Language - The only known documentation for the VIOLET language. (Possibly still incomplete.)