feat: Add Walrus Operator (:=) assignment expression

Author: MrXploisLite

FEATURES.md

@@ -10,6 +10,7 @@ CodingYok adalah bahasa pemrograman Indonesia dengan fitur modern. Dokumen ini m
 
 | Feature | Description |
 |---------|-------------|
+| Walrus Operator | `(x := value)` assignment expression |
 | Ternary Expression | `x jika kondisi kalau_tidak y` inline conditional |
 | Slicing | `arr[start:stop:step]` untuk list dan string |
 | Tuple Unpacking | `a, b = [1, 2]` dan `untuk x, y dalam items` |
@@ -196,6 +197,27 @@ hasil = ["genap" jika n % 2 == 0 kalau_tidak "ganjil" untuk n dalam angka]
 
 ---
 
+## 🦭 Walrus Operator
+
+```codingyok
+# Assignment expression - assign and return value
+tulis((x := 10))  # prints 10, x is now 10
+
+# In conditions
+jika (n := panjang(data)) > 3:
+    tulis(f"List punya {n} elemen")
+
+# In while loops
+selama (line := baca_baris()):
+    tulis(line)
+
+# With calculations
+tulis(f"Total: {(total := a + b)}")
+tulis(f"Variable: {total}")
+```
+
+---
+
 ## 🎯 Pattern Matching
 
 ```codingyok

src/codingyok/ast_nodes.py

@@ -71,6 +71,17 @@ def accept(self, visitor):
         return visitor.visit_ternary(self)
 
 
+@dataclass
+class WalrusExpression(Expression):
+    """Walrus/assignment expression (name := value)"""
+
+    name: str
+    value: Expression
+
+    def accept(self, visitor):
+        return visitor.visit_walrus(self)
+
+
 @dataclass
 class UnaryExpression(Expression):
     """Unary operations (-a, bukan a, etc.)"""

src/codingyok/interpreter.py

@@ -764,6 +764,12 @@ def visit_ternary(self, expr) -> Any:
         else:
             return self.evaluate(expr.false_value)
 
+    def visit_walrus(self, expr) -> Any:
+        """Visit walrus expression (name := value)"""
+        value = self.evaluate(expr.value)
+        self.environment.define(expr.name, value)
+        return value
+
     def visit_unary(self, expr: UnaryExpression) -> Any:
         """Visit unary expression"""
         operand = self.evaluate(expr.operand)

src/codingyok/parser.py

@@ -477,6 +477,22 @@ def primary(self) -> Expression:
             return IdentifierExpression(self.previous().value)
 
         if self.match(TokenType.LEFT_PAREN):
+            # Check for walrus operator (name := value)
+            if self.check(TokenType.IDENTIFIER):
+                # Save position to backtrack if not walrus
+                saved_pos = self.current
+                name_token = self.advance()
+                if self.match(TokenType.WALRUS):
+                    value = self.expression()
+                    self.consume(
+                        TokenType.RIGHT_PAREN,
+                        "Diharapkan ')' setelah walrus expression"
+                    )
+                    return WalrusExpression(name_token.value, value)
+                else:
+                    # Not walrus, backtrack
+                    self.current = saved_pos
+
             expr = self.expression()
             self.consume(TokenType.RIGHT_PAREN, "Diharapkan ')' setelah ekspresi")
             return expr

src/codingyok/tokens.py

@@ -78,6 +78,7 @@ class TokenType(Enum):
 
     # Assignment
     ASSIGN = auto()  # =
+    WALRUS = auto()  # :=
     PLUS_ASSIGN = auto()  # +=
     MINUS_ASSIGN = auto()  # -=
     MULTIPLY_ASSIGN = auto()  # *=
@@ -177,6 +178,7 @@ def __repr__(self) -> str:
     ">": TokenType.GREATER_THAN,
     ">=": TokenType.GREATER_EQUAL,
     "=": TokenType.ASSIGN,
+    ":=": TokenType.WALRUS,
     "+=": TokenType.PLUS_ASSIGN,
     "-=": TokenType.MINUS_ASSIGN,
     "*=": TokenType.MULTIPLY_ASSIGN,