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

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

Breaking parse-tree change for editor textobjects and code navigation. Every scoped construct now exposes its content as a single node via a body field (e.g. (page_declaration body: (declaration_body …)), (code_block (begin_keyword) body: (statement_block …) (end_keyword))), instead of a flat list of direct children. This powers Helix / nvim-treesitter textobjects (@class.inside, @function.inside, @parameter) via the new queries/textobjects.scm, plus a parameters field on procedures/triggers/events.

Tree-walkers and structural queries must descend through the body field — see CHANGELOG.md for the full migration guide.

cargo add tree-sitter-al

use tree_sitter::Parser;

let mut parser = Parser::new();
let language = tree_sitter_al::LANGUAGE;
parser.set_language(&language.into()).expect("Error loading AL grammar");
let tree = parser.parse("codeunit 50100 MyCodeunit { }", None).unwrap();
println!("{}", tree.root_node().to_sexp());

Query constants are also available:

use tree_sitter_al::{HIGHLIGHTS_QUERY, TAGS_QUERY, LOCALS_QUERY, FOLDS_QUERY, INDENTS_QUERY, TEXTOBJECTS_QUERY};

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())

npm install tree-sitter-al

Download from GitHub Releases:

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

• 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.

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

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

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

For grammar refactors, the parse-tree diff harness proves a change is zero-behavior-change by re-parsing every production file and asserting byte-identical trees:

./tools/tree-harness.sh snapshot ./BC.History .snapshots/bc   # baseline
./tools/tree-harness.sh verify   ./BC.History .snapshots/bc   # verify after a change

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)

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

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