hakorune/docs/development/current/main/phase216-selfhost-if-sum-production.md

Phase 216: Selfhost If-Sum Production Test

Overview

Phase 216 validates that Pattern 3 if-sum implementation (Phase 213-215) works correctly with actual selfhost test cases.

Status: ✅ COMPLETE - All production tests passing with correct RC values

Test Results

Primary Target: phase212_if_sum_min.hako

File: apps/tests/phase212_if_sum_min.hako Test Case: Loop with conditional accumulator (i=0..2, sum counts i>0)

static box IfSumTest {
    sum_def_count(defs) {
        local sum = 0
        local i = 0
        local len = 3

        loop(i < len) {
            if i > 0 {
                sum = sum + 1      // Conditional update
                print(sum)
            } else {
                print(0)
            }
            i = i + 1
        }
        return sum
    }

    main() {
        local result = IfSumTest.sum_def_count(0)
        return result
    }
}

Expected: RC=2 (sum=1 at i=1, sum=2 at i=2) Actual: RC=2 ✅

Regression Tests

All existing loop patterns still passing:

Test File	Expected	Actual	Status
loop_if_phi.hako (P3)	RC=2	RC=2	✅ PASS
loop_min_while.hako (P1)	RC=2	RC=2	✅ PASS
joinir_min_loop.hako (P2)	RC=2	RC=2	✅ PASS

Design Validation

Pattern 3 If-Sum Flow

Phase 216 confirms the complete data flow for Pattern 3 if-sum:

Source Code (phase212_if_sum_min.hako)
    ↓
Parser (Nyash/Hakorune)
    ↓
AST with Loop + If Statement
    ↓
Pattern Detection: Pattern3IfPhi
    ↓
JoinIR Lowerer (loop_with_if_phi_if_sum.rs)
    ├─ Extracts: loop condition, if condition, updates
    └─ Creates: JoinFragmentMeta with expr_result
    ↓
JoinInlineBoundary (with_expr_result)
    ↓
JoinIRConversionPipeline
    ├─ Merges blocks
    ├─ Creates exit PHI for sum
    └─ Returns merge_result (exit PHI ValueId)
    ↓
Pattern3 Dispatcher
    └─ Returns expr_result (not Void)
    ↓
Final MIR Function
    ├─ Loop produces ValueId (sum)
    └─ Return statement uses that ValueId
    ↓
VM Execution
    └─ RC=2 (actual sum value, not 0)

Architecture Verification

Phase 215-2 Fixes Confirmed

✅ Fix 1 Verified: JoinIR lowerer creates expr_result

• loop_with_if_phi_if_sum.rs uses with_expr_result(sum_final, exit_meta)
• expr_result properly carries sum's exit PHI ValueId

✅ Fix 2 Verified: Boundary builder passes expr_result

• pattern3_with_if_phi.rs calls .with_expr_result(Some(expr_id))
• expr_result flows to ExitLineReconnector

✅ Fix 3 Verified: Final return uses merge result

• Pattern dispatcher returns expr_val instead of Void
• Loop result (RC=2) propagates to main's return statement

ExprResult Exit Contract

Pattern 3 now matches Pattern 2's behavior:

• Expr-position loops: Return actual computation result
• Statement-position loops: Return Void, update variable_map only
• Unified contract: Consistent with Pattern 2 (Phase 172/190)

Implementation Quality

Code Cleanliness

• No special casing for expr_result in final return
• Conditional return based on merge_result (Option)
• Follows established Pattern 2 pattern

No Regressions

• All existing tests still passing
• Pattern 1/2/4 behavior unchanged
• Legacy P3 mode unaffected

Documentation

• Phase 215 design doc complete
• Phase 212 doc updated with RC=2 success
• This Phase 216 report documents production validation

Lessons Learned

1. ExprResult Contract Importance: Phase 215 fixes were essential

   • Without proper expr_result propagation, RC=0 problem was unfixable
   • Pattern 2 reference implementation was key to understanding correct flow

2. AST-Based Lowering Works: if-sum pattern extraction reliable

   • Loop condition extraction works
   • If condition extraction works
   • Update extraction works
   • Exit PHI handling correct

3. Minimal Changes Approach: Phase 216 needed no fixes

   • All work was in Phase 213-215
   • Production validation just confirmed Phase 215 sufficiency
   • Risk minimal, confidence high

Future Work

Phase 217: Multi-Carrier If-Sum

• Extend to sum+count pattern (2 accumulators)
• Pattern already supports (Phase 214 dynamic join_inputs)
• Test file candidate: Candidate 2 from Phase 211 search

Phase 218: Nested If-Else

• Complex conditional patterns
• Test file candidate: esc_json() from Phase 211 search
• Validates nested if handling inside loops

Phase 219: JsonParser Integration

• Apply if-sum pattern to actual JsonParser loops
• First target: numeric processing loop
• Validates selfhost compiler real use case

Files Modified

No source code changes in Phase 216 - all fixes were in Phase 215.

Summary

Phase 216 successfully validates that Pattern 3 if-sum implementation is production-ready:

• ✅ Target test (phase212_if_sum_min.hako) returns RC=2
• ✅ All regression tests passing
• ✅ ExprResult contract verified
• ✅ No additional bugs found

The complete Phase 213-215 work (AST-based if-sum lowering + ExprResult exit contract) is now validated on production test case. Ready to proceed with multi-carrier and nested patterns (Phase 217+).