Hello, World!

The smallest useful FlipJump program is three lines.

The program

Save this as hello.fj:

stl.startup
stl.output "Hello, World!\n"
stl.loop

Run it:

fj hello.fj

Output:

Hello, World!

That’s it. No headers, no main, no imports — the standard library is implicitly available because the fj tool includes it.

Note

fj hello.fj both assembles and runs the program. To assemble only (writing a .fjm binary), use fj -a hello.fj. To run an already-assembled binary, use fj -r hello.fjm.

What just happened

Three macro calls, each from the standard library:

stl.startup

Initialises the IO opcode address (see Input / Output). This is the lightest startup variant — enough for output-only programs. Heavier variants (stl.startup_and_init_pointers, stl.startup_and_init_all) also set up pointer tables, hex truth tables, and the stack — needed when you use the bit.pointers.* / hex.* / stack-based macros. See Anatomy.

stl.output "Hello, World!\n"

A loop that converts each character of the string to its 8-bit ASCII code, then flips the IO opcode 8 times (LSB first) to emit one byte to stdout. It expands to roughly 13 chars * 8 bits/char * ~3 ops/bit = ~300 FlipJump operations.

stl.loop

The halt. Expands to ;$ - dw — a self-loop on the current instruction whose flip address is 0 (outside the instruction body), which is the FlipJump runtime’s halt condition.

Tip

Want to skip the local install? Paste the same three lines into the FlipJump IDE and click Run. The IDE runs the exact same assembler + interpreter compiled to WebAssembly.

Variations

Print a number in decimal: notice that the variable x is declared as a DATA LABEL after stl.loop, not inline with the code. FlipJump variables are regions of program memory the code reads via self-modifying jumps — they have to sit outside the executable path.

stl.startup
bit.print_dec_uint 32, x
stl.loop

x: bit.vec 32, 12345

Echo a hex digit from stdin: same pattern — variable below the halt.

stl.startup
hex.input_hex input_buf
hex.output input_buf
stl.loop

input_buf: hex.hex

(The exact STL macro signatures may change between releases; the auto-generated per-macro pages under Standard Library always reflect the pinned upstream version.)

What’s next

Read Anatomy of a FlipJump program to understand the broader structure — when to call which startup_* macro, how memory gets laid out, and the conventions you’ll see across STL macros.

Or jump straight into the Standard Library to browse what’s available.