tree-sitter-al

A tree-sitter parser for the AL programming language used in Microsoft Dynamics 365 Business Central.

Parser Status

Validated against 15,358 production AL files from the Business Central codebase:

Metric	Value
Success rate	100% (15,358 / 15,358 files)
Tests	1,404
parser.c size	~11 MB
grammar.js	~3,100 lines
Named keywords	82 (queryable via highlights/tags)
Scanner tokens	8 (stateful, depth-tracking)
Query files	5 (highlights, locals, tags, indents, folds)

Installation

Python (tree-sitter 0.24+)

pip install tree-sitter-al

import tree_sitter
import tree_sitter_al

lang = tree_sitter.Language(tree_sitter_al.language())
parser = tree_sitter.Parser(lang)
tree = parser.parse(b'codeunit 50100 MyCodeunit { }')
print(tree.root_node.sexp())

Node.js

npm install tree-sitter-al

Pre-built binaries

Download from GitHub Releases:

File	Platform	Use case
`tree-sitter-al.wasm`	All	web-tree-sitter
`tree-sitter-al.so`	Linux x86_64	ast-grep, native bindings
`tree-sitter-al.dll`	Windows x86_64	ast-grep, native bindings
`tree-sitter-al.dylib`	macOS ARM64	ast-grep, native bindings

V2 Architecture

The grammar was rewritten from scratch in March 2026, achieving a 10x reduction in parser size while improving correctness.

Before / After

Metric	V1	V2
parser.c	106 MB (can't push to GitHub)	10.6 MB
Errors	14	0
Success rate	99.91%	100%
Symbols	2,249	~740
States	29,126	~5,300
grammar.js	8,500 lines	~3,100 lines
Tests	1,225	1,404
Keywords	invisible in queries	82 named nodes
Query files	3 (partial)	5 (comprehensive)

Key design decisions

Stateful external scanner — 8 scanner tokens handle property disambiguation, depth tracking (#if/#endif nesting), named begin/end keywords at depth 0, and split-construct detection via lookahead.
Parse structure, don't validate — Accept any Name = Value ; as a property. Semantic validation belongs in linters/LSP servers, not the parser.
Generic preprocessor — One preproc_conditional rule + ~15 dedicated rules for genuinely complex split constructs (begin/end, var/begin, brace-close across #if/#else branches).
82 named keyword nodes — All keywords including begin/end are named nodes, enabling proper syntax highlighting and code navigation queries.

See docs/v2-blog-post-notes.md for the full rewrite narrative.

Development

Prerequisites

Node.js (v16+)
tree-sitter CLI: npm install -g tree-sitter-cli

Building

tree-sitter generate    # Generate parser from grammar.js
tree-sitter test        # Run test suite

Validation

./validate-grammar.sh        # Quick: generation, tests, orphan/duplicate detection
./validate-grammar.sh --full # Full: includes production AL file parsing

Parsing AL files

tree-sitter parse path/to/file.al
tree-sitter parse path/to/file.al -d    # Debug output
tree-sitter parse path/to/file.al -q    # Quiet (errors only)

Key files

File	Purpose
`grammar.js`	Main grammar definition
`src/scanner.c`	External scanner (8 tokens: property, depth tracking, named begin/end, split detection)
`test/corpus/`	Test suite (1,404 tests)
`queries/`	Syntax highlighting, code navigation, folding, indentation

Contributing

See CLAUDE.md for detailed development guidelines including architecture, debugging, and conventions.

Author: Torben Leth (sshadows@sshadows.dk) License: MIT (see LICENSE)

tree-sitter-al 2.3.0