Makar BASIC (`basic.elf`)

A small C64-flavoured, line-numbered BASIC interpreter that runs as a ring-3 userland program. Source: src/userspace/basic.c.

basic                 interactive REPL (READY.)
basic prog.bas        load a .bas file, RUN it, then exit

Integer-only by design. Makar doesn’t initialise the x87 FPU or save/restore it across context switches, so ring-3 floating point would corrupt under preemption. All arithmetic is 32-bit signed; fractional work uses fixed-point scaled integers (see the mandelbrot sample).

REPL

Type a line beginning with a number to store/replace a program line; an empty body deletes the line. Anything else runs immediately.

Command	Effect
`RUN`	Execute the stored program from the lowest line
`LIST`	Print the program
`NEW`	Clear the program + variables
`BYE` / `EXIT` / `QUIT`	Leave the interpreter

Ctrl-C is RUN/STOP: it breaks a running program back to the READY. prompt (BREAK IN n); a second Ctrl-C at the prompt exits to the shell. In file mode Ctrl-C exits straight to the shell.

Statements

PRINT (?), LET/NAME=expr, IF cond THEN <stmt|line>, GOTO, GOSUB/RETURN, FOR..TO..STEP..NEXT, INPUT, REM, END/STOP, PAUSE n (wait n centiseconds, honours Ctrl-C), CLS, and graphics PLOT/LINE/RECT/COLOR. Multiple statements per line with :.

Expressions

+ - * / MOD, comparisons = <> < > <= >= (yield -1/0), AND/OR, unary -, parentheses. Functions: ABS(), SGN(), RND(n) (0..n-1), and the screen-size helpers XMAX / YMAX (last drawable pixel column/row). Variables are 1–2 chars (a letter then optional letter/digit).

Graphics

Drawing rides the kernel’s SYS_DRAW_LINE at native VESA resolution (a 1-pixel line is a point). In VGA-text mode the graphics statements print ?NO GRAPHICS.

Statement	Effect
`COLOR c`	Set draw colour (`c` 0–15 = 16-colour palette, or a raw 0xRRGGBB)
`PLOT x,y[,c]`	Plot one pixel
`LINE x0,y0,x1,y1[,c]`	Draw a line
`RECT x0,y0,x1,y1[,c]`	Filled rectangle

YMAX excludes the bottom makmux status row, so a program filling 0..YMAX fills the screen without clipping the bar. A finished graphics program waits for a keypress before exiting so the shell’s post-exit screen restore doesn’t wipe it instantly.

Samples

Shipped in /apps:

mandelbrot.bas — full-screen Mandelbrot via fixed-point integers (scale 1000) drawn as a grid of RECT blocks across XMAX/YMAX.
lines.bas — bouncing-endpoint string-art moiré; accumulates until Ctrl-C.