visitor

AST Visitor and Transformer for Patitas.

Provides a base visitor class with match-based dispatch and an immutable transform function for rewriting frozen ASTs.

Example — collect all headings:

class HeadingCollector(BaseVisitor[None]):
    def __init__(self) -> None:
        self.headings: list[Heading] = []

    def visit_heading(self, node: Heading) -> None:
        self.headings.append(node)

collector = HeadingCollector()
collector.visit(doc)

Example — shift heading levels:

def shift_headings(node: Node) -> Node:
    if isinstance(node, Heading):
        new_level = min(node.level + 1, 6)
        return dataclasses.replace(node, level=new_level)
    return node

new_doc = transform(doc, shift_headings)

Thread Safety:

Visitors are NOT shared across threads by default (they may accumulate
mutable state). Create a new visitor per thread. The transform function
is pure — safe to call from any thread.