# Enhanced Case Statements - Implementation Summary

## 🎉 Implementation Complete - All Tests Passing!

### **Primary Goal Achieved: FizzBuzz Implementation**
```plaintext
fizzbuzz_test : n ->
  when (n % 3) (n % 5) is
    0 0 then "FizzBuzz"
    0 _ then "Fizz"
    _ 0 then "Buzz"
    _ _ then n;

// Test Results:
fizzbuzz_test 15;  // "FizzBuzz"
fizzbuzz_test 3;   // "Fizz"
fizzbuzz_test 5;   // "Buzz"
fizzbuzz_test 7;   // 7
```

### **New Capabilities Added**

#### 1. **Multi-value Patterns with Expressions**
```plaintext
// Complex expressions in parentheses
when (x % 2) (y % 2) is
  0 0 then "both even"
  0 1 then "x even, y odd"
  1 0 then "x odd, y even"
  1 1 then "both odd";
```

#### 2. **Table Access in When Expressions**
```plaintext
user : {role: "admin", level: 5};

when u.role is
  "admin" then "admin user"
  "user" then "regular user"
  _ then "unknown role";
```

#### 3. **Function Calls in When Expressions** (with parentheses)
```plaintext
is_even : n -> n % 2 = 0;

when (is_even n) is
  true then "even number"
  false then "odd number";
```

#### 4. **Parenthesized Expressions in Patterns**
```plaintext
when (complex_func x y) is
  result then "matched"
  _ then "no match";
```

### **Language Design Decisions**

#### **Function Calls Require Parentheses**
This is a deliberate design choice for clarity and consistency:

**✅ Correct:**
```plaintext
when (is_even n) is true then "even"
when (complex_func x y) is result then "matched"
```

**❌ Incorrect:**
```plaintext
when is_even n is true then "even"  // Ambiguous parsing
```

**Benefits:**
- **Zero breaking changes** - No existing code affected
- **Clear intent** - Parentheses make function calls explicit
- **Language consistency** - Matches other disambiguation patterns
- **Parser simplicity** - Cleaner, more maintainable code

### **Backward Compatibility**

**✅ Perfect Backward Compatibility:**
- All existing when expressions continue to work unchanged
- Simple value matching: `when n is 0 then 1`
- Comparison patterns: `when score is score >= 90 then "A"`
- Multi-value patterns: `when x y is 0 0 then "both zero"`
- Wildcard patterns: `when n is _ then "other"`

### **Test Results**

**✅ All Tests Passing:**
- `tests/22_parser_limitations.txt` - All enhanced features working
- `tests/07_case_expressions.txt` - Backward compatibility confirmed
- `tests/08_first_class_functions.txt` - No regressions
- `tests/10_standard_library.txt` - Standard library intact
- Custom FizzBuzz tests - Primary goal validated

### **Implementation Details**

#### **Parser Changes Made:**
1. **Enhanced `parseWhenExpression()`** - Uses `parsePrimary()` for complex values
2. **Added parenthesized expression support** - Patterns can now handle `(expr)`
3. **Improved function call detection** - Better argument parsing in patterns
4. **Maintained backward compatibility** - All existing patterns work unchanged

#### **Key Technical Achievements:**
- **Multi-value patterns with expressions** - Enables tuple-like pattern matching
- **Table access in when expressions** - Full table property access support
- **Function calls in when expressions** - With parentheses for clarity
- **Zero breaking changes** - Perfect backward compatibility

### **Use Cases Enabled**

#### 1. **FizzBuzz and Similar Problems**
```plaintext
// Multiple condition checking
when (n % 3) (n % 5) is
  0 0 then "FizzBuzz"
  0 _ then "Fizz"
  _ 0 then "Buzz"
  _ _ then n;
```

#### 2. **Complex Data Validation**
```plaintext
// Multi-field validation
when (validate_name name) (validate_age age) is
  true true then "valid user"
  true false then "invalid age"
  false true then "invalid name"
  false false then "invalid user";
```

#### 3. **Table-based Pattern Matching**
```plaintext
// User role checking
when user.role is
  "admin" then "admin access"
  "user" then "user access"
  _ then "no access";
```

### **Future Enhancements**

The foundation is now in place for:
- **Helper combinators** for common pattern matching scenarios
- **Pattern matching utilities** for complex pattern construction
- **Performance optimizations** for common patterns
- **Additional pattern types** (destructuring, guard clauses, etc.)

### **Conclusion**

**🎉 Mission Accomplished!**

The enhanced case statements implementation successfully:
- ✅ **Solves the FizzBuzz problem** - Primary goal achieved
- ✅ **Enables complex pattern matching** - Multi-value patterns with expressions
- ✅ **Maintains backward compatibility** - Zero breaking changes
- ✅ **Provides clear language design** - Parentheses for function calls
- ✅ **Passes all tests** - Implementation validated and production-ready

The language now supports sophisticated pattern matching scenarios while maintaining its functional programming philosophy and existing code compatibility.