# pattern_matching

URL: /kida/api/compiler/statements/pattern_matching/
Section: statements
Description: Pattern matching statement compilation for Kida compiler.

Provides mixin for compiling match/case statements.

Extracted from control_flow.py for module focus (RFC: compiler decomposition).
Uses inline TYPE_CHECKING declarations for host attributes.
See: plan/rfc-mixin-protocol-typing.md

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Module

#
`compiler.statements.pattern_matching`

Pattern matching statement compilation for Kida compiler.

Provides mixin for compiling match/case statements.

Extracted from control_flow.py for module focus (RFC: compiler decomposition).
Uses inline TYPE_CHECKING declarations for host attributes.
See: plan/rfc-mixin-protocol-typing.md

1Class

## Classes

`PatternMatchingMixin`

3

▼

Mixin for compiling match/case statements.

Host attributes and cross-mixin dependencies are declar…

Mixin for compiling match/case statements.

Host attributes and cross-mixin dependencies are declared via inline
TYPE_CHECKING blocks.

#### Methods

Internal Methods
3

▼

`_compile_match`

1

`list[ast.stmt]`

▼

Compile {% match expr %}{% case pattern [if guard] %}...{% end %}.

Generates c…

`def _compile_match(self, node: Match) -> list[ast.stmt]`

Compile {% match expr %}{% case pattern [if guard] %}...{% end %}.

Generates chained if/elif comparisons with structural pattern matching
and variable binding support.

Generates:
_match_subject_N = (site.logo, site.logo_text)
if isinstance(_match_subject_N, (list, tuple)) and len(_match_subject_N) == 2:
logo = _match_subject_N[0]
if logo:
...

Valueless match (switch-true):
{% match %}
{% case _ if user.is_admin %}Admin
{% case _ %}Member
{% end %}

When subject is None, generates pure if/elif/else using guard expressions only.

##### Parameters

Name
Type
Description

`node`
`—`

##### Returns

`list[ast.stmt]`

`_compile_valueless_match`

1

`list[ast.stmt]`

▼

Compile valueless {% match %} as pure if/elif/else chain.

Each case must use w…

`def _compile_valueless_match(self, node: Match) -> list[ast.stmt]`

Compile valueless {% match %} as pure if/elif/else chain.

Each case must use wildcard pattern (_) with an optional guard.
Non-wildcard patterns are a compile error since there's no subject.

{% match %}
{% case _ if x > 0 %}positive
{% case _ if x == 0 %}zero
{% case _ %}negative
{% end %}

Generates:

```
if x > 0:
    _append('positive')
elif x == 0:
    _append('zero')
else:
    _append('negative')
```

##### Parameters

Name
Type
Description

`node`
`—`

##### Returns

`list[ast.stmt]`

`_make_pattern_match`

2

`tuple[ast.expr, list[tup…`

▼

Generate match test and bindings for a pattern.

`def _make_pattern_match(self, pattern: Node, subject_ast: ast.expr) -> tuple[ast.expr, list[tuple[str, ast.expr]]]`

##### Parameters

Name
Type
Description

`pattern`
`—`

`subject_ast`
`—`

##### Returns

`tuple[ast.expr, list[tuple[str, ast.expr]]]`

(test_ast, [(name, value_ast), ...])