Introduction

rust-plc is an open-source IEC 61131-3 Structured Text compiler toolchain built in Rust. It provides everything you need to write, analyze, and execute PLC programs:

Compiler — Parses Structured Text source code, performs semantic analysis with 30+ diagnostic checks, and compiles to register-based bytecode
Runtime — A bytecode VM that executes compiled programs in a PLC-style scan cycle loop
LSP Server — Full Language Server Protocol integration with 16 features: diagnostics, hover, go-to-definition, go-to-type-definition, completion, signature help, find all references, rename, document/workspace symbols, document highlight, folding, document links, semantic tokens, formatting, and code actions
DAP Debugger — Full Debug Adapter Protocol support with breakpoints, stepping, variable inspection, and scan-cycle-aware continue
Online Change — Hot-reload compiled programs without stopping the runtime, with automatic variable migration
Monitor Server — WebSocket-based live variable dashboard for real-time trend recording
CLI Tool — st-cli provides check, compile, run, and debug commands for the terminal

What is Structured Text?

Structured Text (ST) is one of the five programming languages defined by the IEC 61131-3 standard for programmable logic controllers (PLCs). It’s a high-level, Pascal-like language used extensively in industrial automation:

PROGRAM TemperatureControl
VAR
    sensor_temp : REAL := 22.0;
    setpoint    : REAL := 50.0;
    heater_on   : BOOL := FALSE;
END_VAR
    IF sensor_temp < setpoint - 2.0 THEN
        heater_on := TRUE;
    ELSIF sensor_temp > setpoint + 2.0 THEN
        heater_on := FALSE;
    END_IF;
END_PROGRAM

Key Features

Feature	Status
Full ST parser with error recovery	✅
30+ semantic diagnostics (type errors, undeclared vars, etc.)	✅
LSP server (16 features: diagnostics, hover, go-to-def, completion, references, rename, formatting, and more)	✅
VSCode extension with syntax highlighting	✅
Bytecode compiler	✅
Runtime VM with scan cycle engine	✅
Debugger (DAP)	✅
Online change (hot reload)	✅
Monitor server (WebSocket live dashboard)	✅
LLVM native compilation	🔜

Quick Example

# Check a file for errors
st-cli check program.st

# Compile and run for 1000 scan cycles
st-cli run program.st -n 1000

# Start the LSP server (used by VSCode)
st-cli serve

Architecture

The toolchain follows the same architecture as rust-analyzer: a Rust core process handles all the heavy lifting, while a thin TypeScript extension bridges to VSCode.

Source (.st) → Parser → AST → Semantics → IR → VM
                              ↓
                          LSP Server → VSCode

Continue to Installation to get started.

Keyboard shortcuts

IEC 61131-3 Structured Text Compiler

Introduction

What is Structured Text?

Key Features

Quick Example

Architecture