Gleam syntax

The parser uses tree-sitter and the AST builder converts accepted syntax into compiler-owned nodes. Syntax that is parsed but not yet executable is preserved as raw syntax with kind, source text, and source span. Later phases can produce targeted diagnostics.

Covered syntax

The AST layer represents current Gleam module syntax, including:

• constants and module attributes
• external functions and external types
• type aliases and custom type definitions
• records, record updates, and field access
• tuples, lists, bit arrays, and strings
• anonymous functions and function values
• pipelines, boolean operators, comparisons, and arithmetic operators
• use, panic, todo, assert, and let assert
• case syntax with guards and multiple subjects
• nested pattern forms

Known unsupported executable forms should fail in the phase responsible for the missing semantics, not in parsing.

AST invariants

AST construction follows these rules:

• reject tree-sitter error nodes
• preserve source order
• preserve source spans on all meaningful nodes
• leave names textual until name resolution
• do not infer types or resolve imports
• preserve raw syntax kind, source text, and span

These invariants keep parsing independent from later compiler phases and make syntax fixtures useful even when runtime support for a construct is incomplete.