Michael Schimmel
a78e72d074
This commit refactors the Binder implementation to better align with the updated scope structure. Key changes include: - Introducing `ExprContext` to distinguish between statement and expression contexts. - Modifying `define_variable` to handle both global and local scope definitions more robustly. - Updating `resolve_variable` to correctly handle upvalue captures, especially for global addresses. - Adjusting `bind` and related functions to use the new `ExprContext`. - Updating the refactoring log to reflect completed phases.
53 lines
2.7 KiB
Markdown
53 lines
2.7 KiB
Markdown
# Development Log: Binder Refactoring & Block Scoping
|
|
|
|
## Status Quo
|
|
- Myc currently uses a flat scope per function.
|
|
- `def` is treated as a side-effect expression that "leaks" into the function scope regardless of nesting (e.g., inside `if` or `do`).
|
|
- This leads to uninitialized variables at runtime if the definition is skipped by control flow.
|
|
|
|
## Goal
|
|
Implement strict **Block Scoping** and distinguish between **Statements** and **Expressions** to eliminate undefined variable states.
|
|
|
|
### Rules
|
|
1. **Block Scoping:** Every `(do ...)` and `if` branch creates a new lexical scope.
|
|
2. **Statements vs. Expressions:**
|
|
- `def` is a **Statement**.
|
|
- Statements have no return value (Void).
|
|
- Statements **cannot** be used as expressions (e.g., as arguments, RHS of assignments, or conditions).
|
|
- Statements **cannot** be the last element of a block (since the block's value is determined by its last expression).
|
|
3. **No Shadowing:** Redefining a symbol within the **same** scope level is an error. Shadowing from outer scopes is allowed (standard lexical scoping).
|
|
4. **Self-Reference:** A variable is only available in its scope **after** its definition is complete (RHS of `def` sees outer scope).
|
|
|
|
## Implementation Plan
|
|
|
|
### Phase 1: Binder Infrastructure (Completed)
|
|
1. [x] Update `CompilerScope` to support hierarchical nesting via a stack in `FunctionCompiler`.
|
|
2. [x] Implement `push_scope` and `pop_scope` in `Binder`.
|
|
3. [x] Refactor `resolve_variable` to traverse the scope stack (inner-to-outer).
|
|
4. [x] Update `define_variable` to enforce "No Shadowing" at the current scope level.
|
|
|
|
### Phase 2: Statement/Expression Validation (Completed)
|
|
1. [x] Introduce a mechanism to track "Context" (Expression vs. Statement) during binding.
|
|
2. [x] Validate that `def` is only used in statement positions.
|
|
3. [x] Enforce that the last node in a `BoundKind::Block` is an expression.
|
|
|
|
### Phase 3: VM Compatibility
|
|
1. [ ] Ensure the VM handles "Void" results from statements correctly.
|
|
2. [ ] (Optional) Optimize stack allocation based on scope depth.
|
|
|
|
---
|
|
|
|
## Log Entries
|
|
|
|
### 2024-05-22: Initialization
|
|
- Analyzed `design-flaw.myc`.
|
|
- Defined the "Statement" concept to solve the uninitialized variable problem.
|
|
- Initialized this log.
|
|
|
|
### Phase 1 & 2 Completed
|
|
- Introduced scope stack into `FunctionCompiler`.
|
|
- Introduced `ExprContext` (`Expression` / `Statement`) in the `Binder`.
|
|
- `def` now acts strictly as a statement.
|
|
- Variables defined inside nested scopes (e.g. inside `if` or `do`) do not leak into outer local scopes anymore.
|
|
- Outstanding behavior to discuss: `def` inside nested scopes at the *root* level still leaks into globals.
|