signallang

A small, safe scripting language for publishing synthetic signals — structured data that changes over time — no eval/exec, no user-defined functions, nothing that reaches outside the value it's computing.

It was designed to drive a ROS2 "fake publisher" (make a topic emit synthetic sensor/status data for testing a subscriber in isolation), but nothing in the language itself is ROS-specific — it's a general way to describe "this value, but changing over time, at this rate, for this long," usable anywhere that pattern shows up.

What's here

This repo ships the full language: the expression layer (arithmetic, comparisons, and/or/not, a function whitelist, terop, and a postfix .s/.m/.ms unit-view operator) and the statement layer on top of it — var, if {} else if {} else {}, repeat/repeat N/for i in A..B, live { } blocks with an automatic per-binding _t, timer()/latching_timer()/.reset(), send hz/dur, string literals, positional array fill, and the default placeholder.

from signallang import evaluate, compile_script

evaluate("sin(t)", {"t": 1.57})
# 0.9999996829318346

evaluate("terop(t < 4.5 and battery > 0, 1, 0)", {"t": 2.0, "battery": 80.0})
# 1.0

compiled = compile_script("temperature = linear(20, 30, 10s);\nsend hz 2 dur inf;")
run = compiled.new_run()
run.step()  # StepResult(value={'temperature': 20.0}, hz=2.0)
run.step()  # StepResult(value={'temperature': 20.5}, hz=2.0)

A script compiles to a small, flat instruction tape (mostly Send, plus SetVar/SetField/Jump/JumpIfFalse/CreateTimer/ResetTimer) and runs as a stepped VM: ScriptRun.step() executes instructions until it hits the next Send tick and returns immediately — no thread, no clock, no sleep() anywhere in compiler.py/vm.py. Real-time pacing between step() calls is the caller's job; run_realtime() is a small opt-in convenience driver (the only place in the package that imports time) for anyone using signallang outside a framework that already owns its own timer loop (like ROS's rclpy.Timer will in a future adapter).

from signallang import run_realtime

run_realtime(compiled, on_send=lambda msg: print(msg))  # blocks, runs in real time

Grammar

Loosest to tightest binding: or → and → not → comparison (< > <= >= == !=, non-chaining — write a > 1 and a < 5, not 1 < a < 5) → + - → * / % → unary +/- → atom.

Whatever names you inject via variables are the only identifiers available beyond the fixed whitelist above — there's no way to reach a name, attribute, or module that wasn't explicitly handed in.

Install

pip install -e .

pip install -e ".[test]" && pytest

Roadmap

What's left is wiring this up to a real message system — a ROS2 adapter (SchemaProvider backed by real message reflection, ROS type-coercion, and a real rclpy.Timer driving step() in place of run_realtime()) that the robohome_ws dashboard's fake-publisher feature would depend on. Nothing in this package itself is ROS-specific, by design.