# Phase 182 Completion Report: JsonParser Simple Loop Implementation (P2/P1 Verification)

**Date**: 2025-12-08
**Status**: ✅ **PARTIAL SUCCESS** - Pattern routing verified, blockers identified
**Goal**: Implement JsonParser simple loops (_parse_number, _atoi, _match_literal) using existing P2/P1 patterns

---

## Executive Summary

Phase 182 successfully verified that Pattern1 (Simple) and Pattern2 (Break) routing and execution work correctly for basic loop patterns. However, we discovered **two fundamental blockers** that prevent the actual JsonParser loops from working:

1. **LoopBodyLocal variable handling** - Current system assumes Trim-specific carrier promotion
2. **String concatenation filter** - Phase 178's conservative rejection of string operations

### Achievement Status

| Task | Status | Notes |
|------|--------|-------|
| 182-1: Design Document | ✅ COMPLETE | phase182-simple-loops-design.md created |
| 182-2: Routing Whitelist | ✅ COMPLETE | Added 3 methods, fixed _match_literal arity |
| 182-3: Pattern Routing | ✅ VERIFIED | P1/P2 route correctly with structure-only mode |
| 182-5: Representative Tests | ✅ PASSING | 2 tests created, both PASS |
| 182-6: Documentation | ✅ COMPLETE | Updated architecture docs + CURRENT_TASK |

---

## Detailed Results

### Task 182-1: Design Document ✅

**File**: `docs/development/current/main/phase182-simple-loops-design.md`

Created comprehensive design memo covering:
- Target loop analysis (3 loops: _parse_number, _atoi, _match_literal)
- Pattern mapping (P2 Break × 2, P1 Simple × 1)
- Pipeline integration strategy (reuse PatternPipelineContext)
- Verification plan (structure-only tracing + representative tests)

**Commit**: `5d99c31c` - "docs(joinir): Add Phase 182 simple loops design memo"

---

### Task 182-2: Routing Whitelist Update ✅

**File**: `src/mir/builder/control_flow/joinir/routing.rs`

**Changes Made**:
1. Added `JsonParserBox._parse_number/2` → P2 Break
2. Added `JsonParserBox._atoi/1` → P2 Break
3. Fixed `JsonParserBox._match_literal` arity: `/2` → `/3` (s, pos, literal)

**Rationale**:
- Phase 181 analysis identified these 3 loops as high-priority, low-difficulty targets
- Verified actual signatures from `tools/hako_shared/json_parser.hako`
- Arity counting follows Nyash convention (excludes implicit `me` parameter)

**Commit**: `be063658` - "feat(joinir): Phase 182-2 Add _parse_number/_atoi to routing whitelist"

---

### Task 182-3: Pattern Routing Verification ✅

**Method**: Used `NYASH_JOINIR_STRUCTURE_ONLY=1` + `NYASH_JOINIR_DEBUG=1` tracing

**Results**:

#### Pattern1 (_match_literal) - ✅ SUCCESS
```bash
[trace:pattern] route: Pattern1_Minimal MATCHED
[joinir/pattern1] Generated JoinIR for Simple While Pattern
[joinir/pattern1] Functions: main, loop_step, k_exit
```

#### Pattern2 (Simple integer loop) - ✅ SUCCESS
```bash
[trace:pattern] route: Pattern2_WithBreak MATCHED
[pattern2/init] PatternPipelineContext: loop_var='i', loop_var_id=ValueId(5), carriers=3
[joinir/pattern2] Phase 170-D: Condition variables verified: {"i", "limit"}
[joinir/pattern2] Generated JoinIR for Loop with Break Pattern
```

#### Full JsonParser Loops - ❌ BLOCKED (Expected)

**Blocker 1**: LoopBodyLocal promotion error
```
[ERROR] ❌ [TrimLoopLowerer] Cannot promote LoopBodyLocal variables ["digit_pos"]:
No promotable Trim pattern detected
```

**Blocker 2**: String operation filter (Phase 178)
```
[pattern2/can_lower] Phase 178: String/complex update detected, rejecting Pattern 2 (unsupported)
[ERROR] ❌ [joinir/freeze] Loop lowering failed: JoinIR does not support this pattern
```

---

### Task 182-5: Representative Tests ✅

Created 2 representative tests in `apps/tests/` (tracked directory):

#### Test 1: Pattern1 (Simple) - `phase182_p1_match_literal.hako`

**Purpose**: Verify Pattern1 routing and execution with early return
**Loop Structure**: Simple while loop with conditional return (matches `_match_literal` logic)

**Result**: ✅ **PASS**
```
Result: MATCH
RC: 0
```

**Verification**:
- Correctly routes to Pattern1_Minimal
- 3 JoinIR functions generated (main, loop_step, k_exit)
- Early return mechanism works correctly
- String matching logic verified

#### Test 2: Pattern2 (Break) - `phase182_p2_break_integer.hako`

**Purpose**: Verify Pattern2 routing and execution with break statement
**Loop Structure**: Integer accumulation with conditional break (simplified _atoi/_parse_number)

**Result**: ✅ **PASS**
```
PASS: P2 Break works correctly
RC: 0
```

**Verification**:
- Correctly routes to Pattern2_WithBreak
- Multi-carrier handling works (result + i)
- Break condition properly evaluated
- Integer arithmetic in carriers verified

**Commit**: `d5b63e09` - "test(joinir): Phase 182-5 Add P1/P2 pattern verification tests"

---

### Task 182-6: Documentation Updates ✅

**Files Updated**:

1. **`docs/development/current/main/joinir-architecture-overview.md`**
   - Added Phase 182 verification status to Section 4.1 (JsonParser ループ空間と P1–P5)
   - Documented blockers and workaround strategies
   - Updated implementation status for _match_literal (✅ verified)

2. **`CURRENT_TASK.md`**
   - Added Phase 182 completion entry with detailed task breakdown
   - Documented both blockers with technical details
   - Created Phase 183 next steps (LoopBodyLocal handling + string ops)

**Commit**: `0772dc3e` - "docs(joinir): Phase 182-6 Update documentation with P1/P2 verification results"

---

## Blockers Identified

### Blocker 1: LoopBodyLocal Variable Handling

**Problem**:
Current system attempts Trim-specific carrier promotion for all LoopBodyLocal variables.

**Example**:
```hako
loop(p < s.length()) {
    local ch = s.substring(p, p+1)      // LoopBodyLocal
    local digit_pos = digits.indexOf(ch) // LoopBodyLocal
    if digit_pos < 0 { break }
    // ...
}
```

**Current Behavior**:
1. LoopConditionScopeBox detects `ch` and `digit_pos` as LoopBodyLocal
2. TrimLoopLowerer tries to promote them to carriers
3. Promotion fails (not a Trim pattern) → Error

**Required Fix**:
- P1/P2 patterns should allow purely local variables (no carrier promotion needed)
- Only Trim pattern requires carrier promotion for `ch`
- Distinction: "LoopBodyLocal used in condition" (Trim) vs "LoopBodyLocal used in body only" (normal)

**Impact**: Blocks _parse_number, _atoi, and most other JsonParser loops

---

### Blocker 2: String Concatenation Filter (Phase 178)

**Problem**:
Phase 178 conservatively rejects string concatenation in Pattern2/4 carrier updates.

**Example**:
```hako
loop(p < s.length()) {
    num_str = num_str + ch  // Rejected by filter
    p = p + 1
}
```

**Current Behavior**:
```rust
UpdateRhs::StringLiteral(_) | UpdateRhs::Other => {
    eprintln!("[pattern2/can_lower] Phase 178: String/complex update detected, rejecting Pattern 2 (unsupported)");
    return false;
}
```

**Required Fix**:
- Gradual enablement of string operations in P2/P4
- Distinguish between:
  - Simple concat: `s = s + literal` (should work)
  - Complex string ops: `s = method_call()` (may need special handling)
- Consider allowing string concat for JsonParser-specific functions

**Impact**: Blocks _parse_number, _parse_string, and all loops with string building

---

## Implementation Strategy (Phase 183+)

### Option A: Minimal Fix (Recommended)

**For Blocker 1 (LoopBodyLocal)**:
1. Add check in `lower_loop_pattern2_with_break()`:
   ```rust
   if !ctx.loop_body_locals.is_empty() && !is_trim_pattern {
       // Allow LoopBodyLocal if not used in loop condition
       // (Trim pattern promotes to carrier, others remain local)
   }
   ```

2. Distinguish between:
   - Trim-style LoopBodyLocal (used in condition) → promote
   - Normal LoopBodyLocal (used in body only) → keep local

**For Blocker 2 (String ops)**:
1. Relax filter in `can_lower()`:
   ```rust
   UpdateRhs::StringLiteral(_) => {
       // Allow simple string literals for now
       // (JsonParser needs this for _parse_number, etc.)
   }
   UpdateRhs::Other => {
       // Still reject complex expressions
       return false;
   }
   ```

2. Add function-specific whitelist if needed

### Option B: Comprehensive Refactor (Future)

1. Create `LoopBodyLocalRole` enum:
   ```rust
   enum LoopBodyLocalRole {
       ConditionCarrier,  // Trim pattern (promote)
       BodyOnly,          // Normal pattern (local)
   }
   ```

2. Extend `UpdateRhs` to track string operation complexity
3. Add gradual string operation support (Phase 184+)

---

## Metrics

### Code Changes

| Metric | Count |
|--------|-------|
| Files Modified | 3 |
| Files Created (docs) | 2 |
| Files Created (tests) | 2 |
| Lines Added (code) | ~10 |
| Lines Added (docs) | ~350 |
| Lines Added (tests) | ~60 |

### Commits

| Commit SHA | Description |
|------------|-------------|
| `5d99c31c` | docs(joinir): Add Phase 182 simple loops design memo |
| `be063658` | feat(joinir): Phase 182-2 Add _parse_number/_atoi to routing whitelist |
| `d5b63e09` | test(joinir): Phase 182-5 Add P1/P2 pattern verification tests |
| `0772dc3e` | docs(joinir): Phase 182-6 Update documentation with P1/P2 verification results |

**Total Commits**: 4
**Build Status**: ✅ All builds successful
**Test Status**: ✅ 2/2 representative tests PASS
**Global Tests**: Not run (blockers prevent JsonParser loops from compiling)

---

## Lessons Learned

### What Worked Well

1. **Structure-based routing** (`NYASH_JOINIR_STRUCTURE_ONLY=1`) is excellent for development
2. **PatternPipelineContext reuse** - No new infrastructure needed
3. **Existing P1/P2 lowerers** - Worked perfectly for basic cases
4. **Phase 181 analysis** - Accurate predictions saved time

### What Needs Improvement

1. **LoopBodyLocal handling** - Too Trim-specific, needs generalization
2. **String operation filter** - Too conservative, needs gradual relaxation
3. **Test coverage** - Need tests for LoopBodyLocal edge cases

### Design Insights

1. **Trim pattern is special** - Requires carrier promotion, but not all patterns do
2. **String ops are common** - JsonParser heavily uses string building
3. **Filter granularity** - Need finer-grained control than "accept all" or "reject all"
4. **Pattern verification approach** - Starting with simplified tests was correct strategy

---

## Recommendations for Phase 183

### High Priority

1. **LoopBodyLocal handling**
   - Add role-based distinction (condition vs body-only)
   - Allow body-only locals in P1/P2 without promotion
   - Keep Trim-specific promotion for condition locals

2. **String concat enablement**
   - Allow simple string concatenation in P2/P4
   - Add safety checks (e.g., carrier type verification)
   - Document supported vs unsupported string operations

### Medium Priority

3. **Test coverage expansion**
   - Add tests for LoopBodyLocal edge cases
   - Add tests for string concat patterns
   - Add negative tests (verify correct rejection)

4. **Documentation refinement**
   - Create decision tree for LoopBodyLocal handling
   - Document string operation support matrix

### Low Priority

5. **Refactoring opportunities**
   - Consider `LoopBodyLocalRole` enum (future)
   - Consider `UpdateRhs` extension for operation types
   - Consider function-specific routing configuration

---

## Conclusion

Phase 182 successfully **verified the foundation** for JsonParser simple loop support:

✅ **Pattern1 and Pattern2 routing works correctly**
✅ **Basic execution verified with representative tests**
✅ **Blockers identified with clear remediation paths**

The blockers are **architectural constraints** rather than bugs:
- LoopBodyLocal promotion is Trim-specific by design
- String operation filter is conservative by design (Phase 178)

**Next Steps**: Phase 183 will address both blockers with minimal, targeted fixes to enable JsonParser loops while maintaining the existing architecture's safety guarantees.

**Success Criteria Met**:
- Pattern routing verified ✅
- Representative tests created ✅
- Blockers documented ✅
- Remediation paths identified ✅
- Documentation updated ✅

**Overall Assessment**: **Successful verification phase** with clear path forward for full implementation in Phase 183.

---

## References

- Design Document: `docs/development/current/main/phase182-simple-loops-design.md`
- Phase 181 Analysis: `docs/development/current/main/phase181-jsonparser-loop-roadmap.md`
- Architecture Overview: `docs/development/current/main/joinir-architecture-overview.md`
- Test Files:
  - `apps/tests/phase182_p1_match_literal.hako`
  - `apps/tests/phase182_p2_break_integer.hako`
- Routing Code: `src/mir/builder/control_flow/joinir/routing.rs`
- Pattern2 Filter: `src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs`