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.