# Phase 143: Canonicalizer Adaptation Range Expansion

## Status
- State: 🎉 Complete (P0)

## P0: parse_number Pattern - Break in THEN Clause

### Objective
Expand the canonicalizer to recognize parse_number/digit collection patterns, maximizing the adaptation range before adding new lowering patterns.

### Target Pattern
`tools/selfhost/test_pattern2_parse_number.hako`

```hako
loop(i < num_str.length()) {
  local ch = num_str.substring(i, i + 1)
  local digit_pos = digits.indexOf(ch)

  // Exit on non-digit (break in THEN clause)
  if digit_pos < 0 {
    break
  }

  // Append digit
  result = result + ch
  i = i + 1
}
```

### Pattern Characteristics

**Key Difference from skip_whitespace**:
- **skip_whitespace**: `if cond { update } else { break }` - break in ELSE clause
- **parse_number**: `if invalid_cond { break } body... update` - break in THEN clause

**Structure**:
```
loop(cond) {
    // ... body statements (ch, digit_pos computation)
    if invalid_cond {
        break
    }
    // ... rest statements (result append, carrier update)
    carrier = carrier + const
}
```

### Implementation Summary

#### 1. New Recognizer (`ast_feature_extractor.rs`)

Added `detect_parse_number_pattern()`:
- Detects `if cond { break }` pattern (no else clause)
- Extracts body statements before break check
- Extracts rest statements after break check (including carrier update)
- Returns `ParseNumberInfo { carrier_name, delta, body_stmts, rest_stmts }`

**Lines added**: ~150 lines

#### 2. Canonicalizer Integration (`canonicalizer.rs`)

- Tries parse_number pattern before skip_whitespace pattern
- Builds LoopSkeleton with:
  - Step 1: HeaderCond
  - Step 2: Body (statements before break)
  - Step 3: Body (statements after break, excluding carrier update)
  - Step 4: Update (carrier update)
- Routes to `Pattern2Break` (has_break=true)

**Lines modified**: ~60 lines

#### 3. Export Chain

Added exports through the module hierarchy:
- `ast_feature_extractor.rs` → `ParseNumberInfo` struct
- `patterns/mod.rs` → re-export
- `joinir/mod.rs` → re-export
- `control_flow/mod.rs` → re-export
- `builder.rs` → re-export
- `mir/mod.rs` → final re-export

**Files modified**: 6 files (8 lines total)

#### 4. Unit Tests

Added `test_parse_number_pattern_recognized()` in `canonicalizer.rs`:
- Builds AST for parse_number pattern
- Verifies skeleton structure (4 steps)
- Verifies carrier (name="i", delta=1, role=Counter)
- Verifies exit contract (has_break=true)
- Verifies routing decision (Pattern2Break, no missing_caps)

**Lines added**: ~130 lines

### Acceptance Criteria

- ✅ Canonicalizer creates Skeleton for parse_number loop
- ✅ RoutingDecision.chosen matches router (Pattern2Break)
- ✅ Strict parity OK (canonicalizer and router agree)
- ✅ Default behavior unchanged
- ✅ quick profile not affected
- ✅ Unit test added
- ✅ Documentation created

### Results

#### Parity Verification

```bash
NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1 ./target/release/hakorune \
  tools/selfhost/test_pattern2_parse_number.hako
```

**Output**:
```
[loop_canonicalizer]   Chosen pattern: Pattern2Break
[choose_pattern_kind/PARITY] OK: canonical and actual agree on Pattern2Break
[loop_canonicalizer/PARITY] OK in function 'main': canonical and actual agree on Pattern2Break
```

**Status**: ✅ **Green parity** - canonicalizer and router agree

#### Unit Test Results

```bash
cargo test --release --lib loop_canonicalizer::canonicalizer::tests::test_parse_number_pattern_recognized
```

**Status**: ✅ **PASS**

### Statistics

| Metric | Count |
|--------|-------|
| New patterns supported | 1 (parse_number) |
| Total patterns supported | 3 (skip_whitespace, parse_number, continue) |
| New Capability Tags | 0 (uses existing ConstStep) |
| Lines added | ~280 |
| Files modified | 8 |
| Unit tests added | 1 |
| Parity status | Green ✅ |

### Comparison: Parse Number vs Skip Whitespace

| Aspect | Skip Whitespace | Parse Number |
|--------|----------------|--------------|
| **Break location** | ELSE clause | THEN clause |
| **Pattern** | `if cond { update } else { break }` | `if invalid { break } rest... update` |
| **Body before if** | Optional | Optional (ch, digit_pos) |
| **Body after if** | None (last statement) | Required (result append) |
| **Carrier update** | In THEN clause | After if statement |
| **Routing** | Pattern2Break | Pattern2Break |
| **Example** | skip_whitespace, trim_leading/trailing | parse_number, digit collection |

### Follow-up Opportunities

#### Immediate (Phase 143 P1-P2)
- [ ] Support parse_string pattern (continue + return combo)
- [ ] Add capability for variable-step updates (escape handling)

#### Future Enhancements
- [ ] Extend recognizer for nested if patterns
- [ ] Support multiple break points (requires new capability)
- [ ] Add signature-based corpus analysis

### Lessons Learned

1. **Break location matters**: THEN vs ELSE clause creates different patterns
2. **rest_stmts extraction**: Need to carefully separate body from carrier update
3. **Export chain**: Requires 6-level re-export (ast → patterns → joinir → control_flow → builder → mir)
4. **Parity first**: Always verify strict parity before claiming success

## SSOT

- **Design**: `docs/development/current/main/design/loop-canonicalizer.md`
- **Recognizer**: `src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs`
- **Canonicalizer**: `src/mir/loop_canonicalizer/canonicalizer.rs`
- **Tests**: Test file `tools/selfhost/test_pattern2_parse_number.hako`

---

**Phase 143 P0: Complete** ✅
**Date**: 2025-12-16
**Implemented by**: Claude Code (Sonnet 4.5)