hakorune/docs/development/current/main/PHASE_224_SUMMARY.md

Phase 224: A-4 DigitPos Promoter - Implementation Summary

Date: 2025-12-10 Status: Core Implementation Complete, Integration Requires Additional Work Branch: main Commits: TBD

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Executive Summary

Phase 224 successfully implemented the DigitPosPromoter Box for A-4 pattern (cascading indexOf) promotion, achieving:

✅ Complete: DigitPosPromoter implementation with full unit test coverage (6/6 tests passing) ✅ Complete: Integration into LoopBodyCondPromoter orchestrator ✅ Complete: Two-tier promotion strategy (A-3 Trim → A-4 DigitPos fallback) ✅ Verified: Promotion detection working correctly in Pattern2 pipeline ⚠️ Partial: Full E2E flow blocked by lowerer integration issue

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Accomplishments

1. Design Document (224-2) ✅

File: docs/development/current/main/phase224-digitpos-promoter-design.md

Key Design Decisions:

• One Box, One Question: DigitPosPromoter handles ONLY A-4 pattern (indexOf-based)
• Separation of Concerns: Trim patterns remain in LoopBodyCarrierPromoter
• Orchestrator Pattern: LoopBodyCondPromoter delegates to specialized promoters
• Bool Carrier: Promote to is_digit_pos (bool) for consistency with A-3 Trim

2. DigitPosPromoter Implementation (224-3) ✅

File: src/mir/loop_pattern_detection/loop_body_digitpos_promoter.rs (467 lines)

Features:

• Pattern Detection: Identifies cascading substring() → indexOf() → comparison
• Comparison Operators: Supports <, >, <=, >=, != (not equality)
• Dependency Validation: Verifies indexOf() depends on another LoopBodyLocal
• Comprehensive Tests: 6 unit tests covering normal/edge cases

Test Results:

cargo test --release --lib digitpos
# running 6 tests
# test result: ok. 6 passed; 0 failed; 0 ignored

3. LoopBodyCondPromoter Integration (224-4) ✅

File: src/mir/loop_pattern_detection/loop_body_cond_promoter.rs

Two-Tier Strategy:

Step 1: Try A-3 Trim promotion (LoopBodyCarrierPromoter)
        ↓ (if fails)
Step 2: Try A-4 DigitPos promotion (DigitPosPromoter)
        ↓ (if fails)
Step 3: Fail-Fast with clear error message

Logs Verify Success:

[cond_promoter] A-3 Trim promotion failed: No promotable Trim pattern detected
[cond_promoter] Trying A-4 DigitPos promotion...
[digitpos_promoter] Phase 224: Found 1 LoopBodyLocal variables: ["digit_pos"]
[digitpos_promoter] A-4 DigitPos pattern promoted: digit_pos → is_digit_pos
[cond_promoter] A-4 DigitPos pattern promoted: 'digit_pos' → carrier 'is_digit_pos'

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Current Limitation: Lowerer Integration Gap

Problem Statement

Symptom: E2E test fails despite successful promotion Root Cause: lower_loop_with_break_minimal performs independent LoopBodyLocal check Result: Promoted variables are detected as "unsupported" by the lowerer

Error Flow

Phase 223.5 (Pattern2) → LoopBodyCondPromoter.try_promote() → SUCCESS ✅
                       ↓
Phase 180-3 (Pattern2) → TrimLoopLowerer.try_lower() → SKIP (not Trim)
                       ↓
Pattern2 Lowerer → lower_loop_with_break_minimal() → Analyze break condition
                 ↓
LoopConditionScopeBox.analyze() → Detects "digit_pos" as LoopBodyLocal
                 ↓
ERROR ❌: "Unsupported condition: uses loop-body-local variables: [\"digit_pos\"]"

Why A-3 Trim Patterns Work

For A-3 Trim patterns, TrimLoopLowerer rewrites the break condition to remove LoopBodyLocal references before passing to lower_loop_with_break_minimal:

// TrimLoopLowerer returns trim_result.condition (rewritten)
let effective_break_condition = trim_result.condition;  // No LoopBodyLocal!

But for A-4 DigitPos (Phase 223.5), we:

• Successfully promote to carrier: digit_pos → is_digit_pos ✅
• Merge carrier into CarrierInfo ✅
• BUT: Break condition AST still contains digit_pos ❌

Root Cause Analysis

The break condition is an AST node containing:

if digit_pos < 0 { break }

After promotion:

• CarrierInfo knows about is_digit_pos carrier ✅
• LoopBodyCondPromoter recorded the promotion ✅
• But: AST node still says digit_pos, not is_digit_pos ❌

When lower_loop_with_break_minimal analyzes the condition:

let cond_scope = LoopConditionScopeBox::analyze(&conditions);
if cond_scope.has_loop_body_local() {
    // ERROR: Still sees "digit_pos" in AST!
}

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Solution Options (Phase 224-continuation)

Option A: AST Rewriting (Comprehensive)

Approach: Rewrite break condition AST to replace promoted variables with carrier references

Implementation:

1. After LoopBodyCondPromoter.try_promote() succeeds
2. Create ASTRewriter to traverse break_condition_node
3. Replace Variable("digit_pos") → Variable("is_digit_pos")
4. Pass rewritten condition to lower_loop_with_break_minimal

Pros: Clean, consistent with Trim pattern flow Cons: AST rewriting is complex, error-prone Effort: ~2-3 hours

Option B: Promoted Variable Tracking (Surgical)

Approach: Add metadata to track promoted variables, exclude from LoopBodyLocal check

Implementation:

1. Add promoted_loopbodylocals: Vec<String> to CarrierInfo
2. In Phase 223.5, record promoted_var in CarrierInfo
3. Modify lower_loop_with_break_minimal signature:

   fn lower_loop_with_break_minimal(
       ...,
       promoted_vars: &[String],  // NEW
   ) -> Result<...>
   

4. In LoopConditionScopeBox::analyze(), filter out promoted_vars:

   if cond_scope.has_loop_body_local_except(promoted_vars) {
       // Only error if non-promoted LoopBodyLocal exists
   }
   

Pros: Minimal changes, surgical fix Cons: Adds parameter to lowerer API Effort: ~1-2 hours

Option C: DigitPosLoopHelper Metadata (Consistent)

Approach: Create DigitPosLoopHelper similar to TrimLoopHelper

Implementation:

1. Create loop_body_digitpos_helper.rs (similar to trim_loop_helper.rs)
2. Attach DigitPosLoopHelper to CarrierInfo in DigitPosPromoter
3. In Phase 223.5, check for digitpos_helper (like trim_helper check at line 321)
4. In lower_loop_with_break_minimal, check CarrierInfo for helpers before error

Pros: Consistent with Trim pattern architecture Cons: More boilerplate Effort: ~2-3 hours

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Recommended Next Steps

Immediate (P0 - Phase 224 Completion)

Goal: Unblock phase2235_p2_digit_pos_min.hako test

Approach: Implement Option B (Promoted Variable Tracking)

Tasks:

1. Add promoted_loopbodylocals field to CarrierInfo
2. Record promoted_var in Phase 223.5 (pattern2_with_break.rs:303)
3. Pass promoted list to lower_loop_with_break_minimal
4. Modify LoopConditionScopeBox to exclude promoted vars
5. Verify E2E test passes

Estimated Time: 1-2 hours Risk: Low (surgical change)

Short-term (P1 - Phase 225)

Goal: Extend to Pattern4 (with continue)

Tasks:

1. Apply same promoted variable tracking to Pattern4
2. Test with parser_box_minimal.hako (skip_ws pattern)
3. Verify no regression in existing Trim patterns

Estimated Time: 1 hour Risk: Low (reuse Option B infrastructure)

Medium-term (P2 - Phase 226)

Goal: A-5/A-6 patterns (multi-variable, cascading)

Tasks:

1. Extend DigitPosPromoter to handle multiple indexOf() calls
2. Support range check patterns (A-6: ch < "0" || ch > "9")
3. Add multi-variable promotion support

Estimated Time: 3-4 hours Risk: Medium (more complex patterns)

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Files Modified

New Files (3)

• docs/development/current/main/phase224-digitpos-promoter-design.md (design doc)
• src/mir/loop_pattern_detection/loop_body_digitpos_promoter.rs (promoter implementation)
• docs/development/current/main/PHASE_224_SUMMARY.md (this file)

Modified Files (2)

• src/mir/loop_pattern_detection/mod.rs (add digitpos_promoter module)
• src/mir/loop_pattern_detection/loop_body_cond_promoter.rs (two-tier integration)

Test Coverage

• Unit tests: 6/6 passing (100%)
• E2E test: 0/1 passing (blocked by lowerer integration)

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Build & Test Status

Build

cargo build --release
# Finished `release` profile [optimized] target(s) in 1m 11s
# 7 warnings (snake_case naming, visibility)

Unit Tests

cargo test --release --lib digitpos
# running 6 tests
# test result: ok. 6 passed; 0 failed; 0 ignored

E2E Test (Current State)

./target/release/hakorune apps/tests/phase2235_p2_digit_pos_min.hako
# [digitpos_promoter] A-4 DigitPos pattern promoted: digit_pos → is_digit_pos ✅
# [cond_promoter] A-4 DigitPos pattern promoted ✅
# ERROR: Unsupported condition: uses loop-body-local variables: ["digit_pos"] ❌

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Technical Debt & Future Work

Code Quality Improvements

1. Fix snake_case warnings in digitpos_promoter.rs (is_indexOf → is_index_of)
2. Add LoopScopeShape visibility annotation (pub(crate) or pub)
3. Extract common AST traversal logic (find_definition_in_body) to shared module

Documentation

1. Add DigitPosPromoter to joinir-architecture-overview.md box catalog
2. Update phase223-loopbodylocal-condition-inventory.md with Phase 224 status
3. Create integration guide for future pattern promoters

Testing

1. Add integration tests for Pattern2+DigitPos combination
2. Add regression tests for Trim patterns (ensure no impact)
3. Add performance benchmarks for promotion detection

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Appendix: Key Design Insights

Why Two Promoters Instead of One?

Question: Why not extend LoopBodyCarrierPromoter to handle A-4 patterns?

Answer: Separation of Concerns

• LoopBodyCarrierPromoter: Equality-based patterns (A-3 Trim)

  • ch == " " || ch == "\t" (OR chain)
  • Single LoopBodyLocal
  • Well-tested, stable

• DigitPosPromoter: Comparison-based patterns (A-4 DigitPos)

  • digit_pos < 0 (comparison)
  • Cascading dependencies (ch → digit_pos)
  • New, experimental

Box-First Principle: "One Box = One Question"

Why Bool Carrier Instead of Int?

Question: Why not preserve digit_pos as int carrier?

Answer: Consistency with Existing Architecture

• A-3 Trim patterns use bool carriers (is_whitespace)
• Pattern2/Pattern4 lowerers expect bool carriers in conditions
• Bool carrier simplifies condition rewriting (just a flag)

Future: Int carrier variant can be added for downstream use (Phase 226+)

Why Not Rewrite AST Immediately?

Question: Why defer AST rewriting to Phase 224-continuation?

Answer: Incremental Development

• AST rewriting is complex and error-prone
• Surgical fix (Option B) unblocks test faster
• Learn from A-3 Trim pattern experience first
• Can refactor to AST rewriting later if needed

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Conclusion

Phase 224 successfully implemented the core promotion logic for A-4 DigitPos patterns, achieving:

• ✅ Comprehensive design document
• ✅ Robust promoter implementation with full test coverage
• ✅ Clean integration into orchestrator pattern
• ✅ Verified promotion detection in Pattern2 pipeline

Remaining Work: Lowerer integration (1-2 hours, Option B approach)

Next Session: Implement Option B (promoted variable tracking) to complete Phase 224 and unblock phase2235_p2_digit_pos_min.hako test.

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References

• Phase 223 Inventory - A-4 pattern specification
• Phase 224 Design - Detailed design document
• JoinIR Architecture - Overall system architecture
• Test File - Minimal A-4 test case