chore(special-vars): complete polish tasks (Phase 8)

[cxxxr]

Summary

Complete the remaining polish tasks for the special variables implementation.

Branch: 002-special-vars-compiler
Spec: specs/002-special-vars-compiler/tasks.md (Phase 8)
Priority: P3 (polish)

Prerequisites

• US1-US3: P1 user stories (completed)
• US4: Gensym support (feat(special-vars): implement gensym function (US4) #4)
• US5: Exception-safe dynamic binding (feat(special-vars): implement exception-safe dynamic binding (US5) #5)

Tasks

From specs/002-special-vars-compiler/tasks.md:

• T059: Update placeholder tests in tests/integration/special-var-test.lisp to real implementations
• T060: Add UNBOUND check code generation option to compile-special-var-ref
• T061: Integration test for closure capturing special variable in tests/integration/special-var-test.lisp

Details

T059: Update Placeholder Tests

Current tests for US4/US5 are placeholders that always pass. Once US4 and US5 are implemented, these need to be converted to real integration tests.

T060: UNBOUND Check

Add optional UNBOUND sentinel checking when accessing special variables:

• Generate code to check if symbol-value equals UNBOUND sentinel
• Signal an error for unbound variable access
• Make this configurable (for performance vs safety trade-off)

T061: Closure + Special Variable Test

Test the interaction between closures and special variables:

(defvar *x* 10)
(let ((f (lambda () *x*)))
  (let ((*x* 20))
    (funcall f)))  ; Should return 20 (dynamic binding)

Related

• Parent issue: Phase 3-8 残タスク: スペシャル変数 → 例外処理 → 標準ライブラリ #3 (Phase 3-8 残タスク)
• Depends on: feat(special-vars): implement gensym function (US4) #4, feat(special-vars): implement exception-safe dynamic binding (US5) #5