feat: add super keyword and parent method access

docs/grammar.bnf

@@ -48,6 +48,7 @@
         KW_CONTINUE="continue"
         KW_CLASS="class"
         KW_THIS="this"
+        KW_SUPER="super"
 
         WHITE_SPACE="regexp:\s+"
 
@@ -98,7 +99,7 @@ factor ::= unary ( ( OP_SLASH | OP_STAR ) unary )* ;
 
 unary ::= ( OP_BANG | OP_MINUS ) unary | call ;
 call ::= primary ( PUNC_LPAREN arguments? PUNC_RPAREN | PUNC_DOT IDENTIFIER )* ;
-primary ::= KW_TRUE | KW_FALSE | KW_NULL | KW_THIS | NUMBER | STRING | IDENTIFIER | PUNC_LPAREN expression PUNC_RPAREN ;
+primary ::= KW_TRUE | KW_FALSE | KW_NULL | KW_THIS | NUMBER | STRING | IDENTIFIER | PUNC_LPAREN expression PUNC_RPAREN | KW_SUPER PUNC_DOT IDENTIFIER ;
 
 function ::= IDENTIFIER PUNC_LPAREN parameters? PUNC_RPAREN block ;
 parameters ::= IDENTIFIER ( PUNC_COMMA IDENTIFIER )* ;

examples/basic/21_super.peb

@@ -6,6 +6,10 @@ class Employee {
     has_responsibilities() {
         return false
     }
+
+    get_title() {
+        return "Employee"
+    }
 }
 
 class Manager < Employee {
@@ -22,6 +26,10 @@ class Boss < Manager {
     get_salary() {
         return 500
     }
+
+    get_title() {
+        return super.get_title() + ", CEO"
+    }
 }
 
 let employee = Employee()
@@ -35,3 +43,7 @@ print(boss, boss.get_salary())
 print(employee, employee.has_responsibilities())
 print(manager, manager.has_responsibilities())
 print(boss, boss.has_responsibilities())
+
+print(employee, employee.get_title())
+print(manager, manager.get_title())
+print(boss, boss.get_title())

src/ast/expr.py

@@ -61,6 +61,10 @@ class Expr(ABC):
         def visit_this_expr(self, expr: ThisExpr) -> T:
             ...
 
+        @abstractmethod
+        def visit_super_expr(self, expr: SuperExpr) -> T:
+            ...
+
 
 @dataclass(frozen=True)
 class AssignExpr(Expr):
@@ -159,3 +163,12 @@ class ThisExpr(Expr):
 
     def accept(self, visitor: Expr.Visitor[T]) -> T:
         return visitor.visit_this_expr(self)
+
+
+@dataclass(frozen=True)
+class SuperExpr(Expr):
+    keyword: Token
+    method: Token
+
+    def accept(self, visitor: Expr.Visitor[T]) -> T:
+        return visitor.visit_super_expr(self)

src/formatter.py

@@ -2,7 +2,7 @@ from enum import Enum, auto
 from typing import Any
 
 from src.ast.expr import Expr, VariableExpr, LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, AssignExpr, LogicalExpr, \
-    CallExpr, SetExpr, GetExpr, ThisExpr, T
+    CallExpr, SetExpr, GetExpr, ThisExpr, T, SuperExpr
 from src.ast.stmt import Stmt, LetStmt, IfStmt, ExpressionStmt, BlockStmt, WhileStmt, ForStmt, FunctionStmt, \
     ReturnStmt, BreakStmt, ContinueStmt, ClassStmt
 
@@ -46,6 +46,9 @@ class Formatter(Expr.Visitor[str], Stmt.Visitor[str]):
     def visit_this_expr(self, expr: ThisExpr) -> str:
         return expr.keyword.lexeme
 
+    def visit_super_expr(self, expr: SuperExpr) -> str:
+        return f"{expr.keyword.lexeme}.{expr.method.lexeme}"
+
     def visit_unary_expr(self, expr: UnaryExpr) -> str:
         return f"{expr.operator.lexeme}{self.format(expr.right)}"
 

src/interpreter/interpreter.py

@@ -1,7 +1,7 @@
 from typing import Any, Optional
 
 from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr, LogicalExpr, \
-    CallExpr, GetExpr, T, SetExpr, ThisExpr
+    CallExpr, GetExpr, T, SetExpr, ThisExpr, SuperExpr
 from src.ast.stmt import Stmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt, WhileStmt, ForStmt, FunctionStmt, \
     ReturnStmt, BreakStmt, ContinueStmt, ClassStmt
 from src.consts import CONSTRUCTOR_NAME
@@ -91,6 +91,15 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
     def visit_this_expr(self, expr: ThisExpr) -> Any:
         return self.look_up_variable(expr.keyword, expr)
 
+    def visit_super_expr(self, expr: SuperExpr) -> Any:
+        distance: int = self.locals.get(expr)
+        superclass: PebbleClass = self.env.get_at(distance, "super")
+        obj: PebbleInstance = self.env.get_at(distance - 1, "this")
+        method: Optional[PebbleFunction] = superclass.find_method(expr.method.lexeme)
+        if method is None:
+            raise PebbleRuntimeError(expr.method, f"Undefined property '{expr.method.lexeme}'.")
+        return method.bind(obj)
+
     def visit_binary_expr(self, expr: BinaryExpr) -> Any:
         left: Any = self.evaluate(expr.left)
         right: Any = self.evaluate(expr.right)
@@ -184,11 +193,20 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
                 raise PebbleRuntimeError(stmt.superclass.name, "Superclass must be a class.")
 
         self.env.define(stmt.name.lexeme, None)
+
+        if stmt.superclass is not None:
+            self.env = Environment(self.env)
+            self.env.define("super", superclass)
+
         methods: dict[str, PebbleFunction] = {}
         for method in stmt.methods:
             func: PebbleFunction = PebbleFunction(method, self.env, method.name.lexeme == CONSTRUCTOR_NAME)
             methods[method.name.lexeme] = func
         klass: PebbleClass = PebbleClass(stmt.name.lexeme, superclass, methods)
+
+        if superclass is not None:
+            self.env = self.env.enclosing
+
         self.env.assign(stmt.name, klass)
 
     def visit_expression_stmt(self, stmt: ExpressionStmt) -> None:

src/interpreter/resolver.py

@@ -4,7 +4,7 @@ from enum import Enum, auto
 from typing import TYPE_CHECKING
 
 from src.ast.expr import Expr, LogicalExpr, VariableExpr, LiteralExpr, GroupingExpr, CallExpr, UnaryExpr, BinaryExpr, \
-    AssignExpr, GetExpr, SetExpr, ThisExpr
+    AssignExpr, GetExpr, SetExpr, ThisExpr, SuperExpr, T
 from src.ast.stmt import Stmt, ForStmt, WhileStmt, LetStmt, ReturnStmt, IfStmt, FunctionStmt, \
     ExpressionStmt, BlockStmt, BreakStmt, ContinueStmt, ClassStmt
 from src.consts import CONSTRUCTOR_NAME
@@ -123,6 +123,9 @@ class Resolver(Expr.Visitor[None], Stmt.Visitor[None]):
             Pebble.token_error(expr.keyword, "Cannot use 'this' outside of a class.")
         self.resolve_local(expr, expr.keyword)
 
+    def visit_super_expr(self, expr: SuperExpr) -> None:
+        self.resolve_local(expr, expr.keyword)
+
     def visit_block_stmt(self, stmt: BlockStmt) -> None:
         self.begin_scope()
         self.resolve(*stmt.statements)
@@ -139,6 +142,9 @@ class Resolver(Expr.Visitor[None], Stmt.Visitor[None]):
                 Pebble.token_error(stmt.superclass.name, "A class cannot inherit from itself.")
             self.resolve(stmt.superclass)
 
+            self.begin_scope()
+            self.scopes[-1]["super"] = True
+
         self.begin_scope()
         self.scopes[-1]["this"] = True
 
@@ -149,6 +155,10 @@ class Resolver(Expr.Visitor[None], Stmt.Visitor[None]):
             self.resolve_function(method, declaration)
 
         self.end_scope()
+
+        if stmt.superclass is not None:
+            self.end_scope()
+
         self.current_class = enclosing_class
 
     def visit_expression_stmt(self, stmt: ExpressionStmt) -> None:

src/keyword.py

@@ -21,4 +21,5 @@ KEYWORDS: dict[str, TokenType] = {
     "continue": TokenType.CONTINUE,
     "class": TokenType.CLASS,
     "this": TokenType.THIS,
+    "super": TokenType.SUPER,
 }

src/parser/parser.py

@@ -1,7 +1,7 @@
 from typing import Optional
 
 from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr, AssignExpr, LogicalExpr, \
-    CallExpr, GetExpr, SetExpr, ThisExpr
+    CallExpr, GetExpr, SetExpr, ThisExpr, SuperExpr
 from src.ast.stmt import Stmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt, WhileStmt, ForStmt, FunctionStmt, \
     ReturnStmt, BreakStmt, ContinueStmt, ClassStmt
 from src.consts import MAX_FUNCTION_ARGS
@@ -367,6 +367,12 @@ class Parser:
         if self.match(TokenType.NUMBER, TokenType.STRING):
             return LiteralExpr(self.previous().value)
 
+        if self.match(TokenType.SUPER):
+            keyword: Token = self.previous()
+            self.consume(TokenType.DOT, "Expected '.' after 'super'.")
+            method: Token = self.consume(TokenType.IDENTIFIER, "Expected superclass method name.")
+            return SuperExpr(keyword, method)
+
         if self.match(TokenType.THIS):
             return ThisExpr(self.previous())
 

src/token.py

@@ -60,6 +60,7 @@ class TokenType(Enum):
     CONTINUE = auto()
     CLASS = auto()
     THIS = auto()
+    SUPER = auto()
 
     # Misc
     COMMENT = auto()