108 lines
4.7 KiB
Markdown
108 lines
4.7 KiB
Markdown
# Concrete syntax tree contract
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This document describes the named nodes and fields intended for consumers such
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as editor integrations, formatters, and structural search. Rules prefixed with `_`
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and rules listed as Tree-sitter supertypes are implementation details and do not
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appear as named wrapper nodes in ordinary trees.
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## Source and declarations
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`source_file` contains declarations, imports, publication declarations, and
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standalone expressions directly. The choice-only `module_item`, `expression`,
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and `value_expression` rules are hidden supertypes.
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`declaration` uses these fields:
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- `name` for a named declaration;
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- `pattern` for a destructuring declaration;
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- `type` for an explicit type;
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- `value` for an initializer.
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The punctuation distinguishes immutable, mutable, typed, and deferred forms.
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Consumers should inspect that punctuation rather than infer the form from the
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set of fields alone.
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## Expressions
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Only expressions that actually contain an operator produce an operator node:
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| Node | Fields |
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| --- | --- |
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| `assignment_expression` | `left`, `operator`, `right` |
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| `range_expression` | `left`, `operator`, `right` |
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| `binary_expression` | `left`, `operator`, `right` |
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| `unary_expression` | `operator`, `operand` |
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| `postfix_expression` | `value`, repeated `operator`; member and index operators additionally expose `member` or `index` |
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| `pipeline_expression` | `input`, followed by stage nodes |
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Precedence-only rules are hidden. For example, `a + b * -c` has one outer and
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one inner `binary_expression`, then a `unary_expression`; it does not contain a
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wrapper for every precedence level.
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Literal leaves are named. Boolean and nil values use `boolean_literal` and
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`nil_literal`; numeric, string, character, and unit literals retain their
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specific nodes. `default_expression` is also named.
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`some`, `ok`, and `err` construct optional and result values. They are prefix
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operators, so `some value` and `ok {x->f}` appear as `unary_expression` nodes
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whose `operator` is the keyword. They bind like `-` and `~`, so `ok x->f`
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wraps `x` and then pipes the result into `f`, while `ok {x->f}` wraps the
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pipeline. The older `|.some`/`|.ok`/`|.err`
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constructors, postfix `value!`, and prefix `!error` are no longer accepted.
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`function_literal` takes one input and owns the `body` field. A pattern with
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one annotation for the whole input, such as `@ value: i32` or
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`@ (left, right): (i32, i32)`, appears as `parameter: (typed_parameter)`.
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The annotation is optional: an input whose type comes from the expected
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function type, such as `@ value` or `@ (left, right)`, is also a
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`typed_parameter` without a `type` field. Component-annotated tuple
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destructuring, such as `@ (left: i32, right)`, appears as
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`parameter: (typed_tuple_pattern)`. A `typed_tuple_pattern` contains at least
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two `typed_tuple_component` nodes, each with an optional `type`. These bind
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components of one tuple input, not separate function arguments. `()` matches
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unit and is a `typed_parameter` over a `unit_pattern`; singleton tuple patterns
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are invalid. Bindings expose `pattern` and, when annotated, `type`; a header
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may also expose `effect` (`->` or `=>`) and `result`.
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## Patterns
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`wrapper_pattern` matches `some`, `ok`, or `err` applied to one pattern atom.
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It exposes `wrapper` (the keyword) and `value` (the inner pattern). `nil` is
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still a `nil_literal` pattern. Sum patterns retain `sum_pattern` with a
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`variant` field.
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## Types
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Meaningful type constructors are named directly:
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| Node | Fields |
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| --- | --- |
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| `function_type` | `input`, `effect`, `result` |
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| `result_type` | `value`, `error` |
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| `optional_type` | `value` |
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| `array_type` | `element` |
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| `map_type` | `key`, `value` |
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| `grouped_type` | `value` |
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| `type_application` | `constructor` followed by its type arguments |
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Primitive, unit, tuple, product, sum, and bits types retain their corresponding
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named nodes. Internal primary/container/result categories are hidden.
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## Trivia and physical lines
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Comments are named extra nodes. Spaces, tabs, and structural newlines remain in
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the source gaps between nodes, so a formatter must retain the original source
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alongside the tree. Leading-operator and pipeline continuations use composite
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tokens containing their newline; this prevents a scope separator from stealing
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a valid continuation and preserves the language's physical-line rules.
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## Compatibility
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Adding nodes or fields is compatible. Removing or renaming a named node or
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field, changing its meaning, or changing which source construct owns it is a
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breaking CST change. Until the package reaches 1.0, such changes require corpus
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snapshot updates and a version change, and must be called out in release notes.
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The Tree-sitter tree is designed for source tooling and error recovery; it does
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not perform semantic validation.
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