iecst

IEC 61131-3 Structured Text parser for Rust.

Overview

iecst is a parser for IEC 61131-3 Structured Text (ST), the high-level programming language used in PLC (Programmable Logic Controller) programming.

Features

• Full ST syntax support - expressions, statements, POUs, declarations
• Minimal dependencies (winnow for parsing)
• Detailed error reporting with source locations
• AST output for further analysis or transformation
• Basic static analysis - type checking, unused variables, code smells

Installation

Add to your Cargo.toml:

[dependencies]
iecst = "0.1"

Quick Start

use iecst::{parse_statement, parse_expression};

// Parse a statement
let stmt = parse_statement("x := 1 + 2;").unwrap();

// Parse an expression
let expr = parse_expression("a AND b OR c").unwrap();

Supported Constructs

Expressions

• Literals: integers, reals, strings, booleans, time literals
• Identifiers and qualified names
• Binary operators: +, -, *, /, MOD, **, AND, OR, XOR, comparisons
• Unary operators: -, NOT
• Function calls: SIN(x), MAX(a, b)
• Array indexing: arr[i], arr[i, j]
• Member access: struct.field

Statements

• Assignment: x := expr;
• IF/THEN/ELSIF/ELSE/END_IF
• CASE/OF/ELSE/END_CASE
• FOR/TO/BY/DO/END_FOR
• WHILE/DO/END_WHILE
• REPEAT/UNTIL/END_REPEAT
• EXIT, RETURN, CONTINUE

Program Organization Units (POUs)

• PROGRAM/END_PROGRAM
• FUNCTION/END_FUNCTION
• FUNCTION_BLOCK/END_FUNCTION_BLOCK

Declarations

• VAR/VAR_INPUT/VAR_OUTPUT/VAR_IN_OUT/VAR_TEMP/VAR_GLOBAL
• TYPE/END_TYPE (structures, enums, arrays, subranges)

Example: Parsing a Function Block

use iecst::parse_pou;

let code = r#"
FUNCTION_BLOCK Counter
    VAR_INPUT
        Reset : BOOL;
    END_VAR
    VAR_OUTPUT
        Count : INT;
    END_VAR
    VAR
        _count : INT := 0;
    END_VAR
    
    IF Reset THEN
        _count := 0;
    ELSE
        _count := _count + 1;
    END_IF;
    
    Count := _count;
END_FUNCTION_BLOCK
"#;

let pou = parse_pou(code).unwrap();
println!("Parsed: {:?}", pou.name);

Static Analysis

use iecst::{parse_pou, analyze_pou};

let code = "FUNCTION Test : INT VAR x : INT; END_VAR x := 1; Test := x; END_FUNCTION";
let pou = parse_pou(code).unwrap();
let diagnostics = analyze_pou(&pou);

for diag in diagnostics {
    println!("[{}] {}", diag.severity, diag.message);
}