The Binder and related types have been refactored to use the new
`NodeKind` enum instead of the previous `BoundKind`. This commit updates
all references to use the new structure, ensuring consistency across the
compiler's AST representation.
Key changes include:
- Replacing `BoundKind` with `NodeKind` in the Binder's `bind` and
`visit` methods.
- Updating pattern matching and field access to reflect the new enum
variants (e.g., `NodeKind::Def` instead of `BoundKind::Define`).
- Adjusting identifier bindings to use the new `IdentifierBinding` enum.
- Reflecting changes in `DefBinding`, `AssignBinding`, and
`LambdaBinding` structures.
- Ensuring all newly created nodes use `NodeKind` and the appropriate
metadata.
The 'again' macro is a new addition to the macro system, allowing for
recursive macro expansion. This commit introduces the necessary AST
nodes, macro expansion logic, and an integration test to ensure its
functionality. The `soa_series.myc` example has also been updated to
demonstrate its usage.