README.md
r/moul/x/vm/bfdemo
A realm that runs Brainfuck programs on chain, a slice at a time.
It is a demo of p/moul/x/vm/bf (the machine) and
p/moul/x/vm/vmkit (the host ABI, the fuel meter, the
instance store), and carries no logic of its own.
What it exists to show is the thing gno realm code cannot do for itself: a
program that runs out of fuel does not fail, it pauses. The realm keeps the
snapshot, and the next caller pays for the next slice. Upload a program, call
Step a few times, and watch one computation finish across several
transactions.
Calls
| function | what |
|---|---|
Upload(src, input, budget) |
compile and store a program, returns its id. Compilation happens here, so a malformed program is rejected by the transaction that submitted it |
Step(id, fuel) |
run one slice and keep the snapshot. Anyone may pay for a slice, not only the owner |
Remove(id) |
delete an instance. Owner only |
Render("/") lists the instances and offers three sample programs.
Render("/<id>") shows one instance: its compiled program, status, fuel, and
output.
Limits
Everything a caller can grow is bounded, because all of it is storage somebody pays a deposit on: 64 instances, 64 KiB of source, 1 KiB of input, 4 KiB of output, 5,000,000 fuel per slice, 30,000 tape cells. A guest that writes past the output cap is trapped rather than truncated, so the rendered output is never a lie.
Untrusted input
A program's source is caller-supplied, and everything outside the eight operators is a comment that may hold anything at all. The page never renders it: it shows the program the machine actually compiled, which cannot contain a backtick or a newline and so cannot break out of its code fence. Guest output is arbitrary bytes and is escaped the same way, backtick included.
No instance is funded, so Host.Send always returns ErrNotGranted. That is
the capability rule doing its job, not a missing feature.
Part of moul/gno-contracts — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage.
Dependency graph:
🧪 Highly experimental — potentially vibe-coded. Not audited; may break, change, or be removed at any time. Do not use with anything of value. Full disclaimer: DISCLAIMER.
