JVS programming

JVS programming

JVS is a text interpreter built into the DOS shell. Store one statement per physical line. Use uppercase keywords and registers A-P. Values are decimal bytes; use 0-255. Arithmetic and the numeric parser wrap at 256. RUN clears the sixteen JVS registers at program start. These guest variables are separate from the CPU registers used by the interpreter.

Editing source	Running the captured arithmetic demo

This captured source multiplies 6 by 7 and outputs 42, then increments 255 to demonstrate byte wrapping and outputs 0. This guide is the language reference; programming help is kept outside the resident kernel.

Syntax	Meaning
PRINT text / ECHO text	Print literal remainder of line and newline
STORE value A	Put decimal value in a register
ADD A B C	C = A + B
SUB A B C	C = A - B
MULTIPLY A B C	C = A * B
INC A	Increment A
OUTPUT A	Print unsigned decimal register value
GOTO line	Jump to 1-based physical source line
IF A value line	Jump if A equals literal value
REM text / ; text	Comment line
BEEP, CLS / CLEAR	Tone or clear screen
JCTRL	End the current source program and open the bundled desktop
END, STOP	End source execution and return to prompt

There are no labels, expressions, quoted string evaluation, functions, or arbitrary pixel commands in this language. PRINT "HI" prints the quotes as part of the text. Use spaces between arguments, not commas. Blank/comment lines still occupy physical line positions when calculating jumps. Use REM or a standalone ; comment; numeric parsing does not support a semicolon immediately following a number.

Arithmetic

STORE 6 A
STORE 7 B
MULTIPLY A B C
OUTPUT C
STORE 255 A
INC A
OUTPUT A
END

This prints 42, then 0. The file is examples/dos/MATH.JVS.

Counting loop

STORE 0 A
OUTPUT A
INC A
IF A 5 6
GOTO 2
PRINT DONE
END

This prints 0 through 4, then DONE. Line 4 jumps to line 6 when A reaches 5; otherwise line 5 returns to line 2. Do not add a leading comment or blank line without adjusting the targets. This file is examples/dos/COUNT.JVS.

Create a source file with EDIT NAME.JVS and save with Esc, or import it through Workshop. Run with RUN NAME.JVS. Fullscreen DOS loads up to 61,200 bytes; JCTRL's resident DOS window loads up to 8,192 bytes. Keep each statement within 100 characters. Tabs imported through Workshop become four spaces. Esc aborts between statements. Errors report the source line and return to DOS; use the syntax table above for reference. Nested RUN from a running script is rejected.

The interpreter shares the shell dispatcher but accepts only the language commands above. Filesystem commands and system shutdown commands are unavailable inside source programs.