feat(interpreter): add enclosing environment parameter

src/interpreter/environment.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+from typing import Any, Optional
+
+from src.interpreter.error import PebbleRuntimeError
+from src.token import Token
+
+
+class Environment:
+    def __init__(self, enclosing: Optional[Environment] = None):
+        self.enclosing: Optional[Environment] = enclosing
+        self.values: dict[str, Any] = {}
+
+    def define(self, name: str, value: Any):
+        self.values[name] = value
+
+    def get(self, name: Token) -> Any:
+        try:
+            return self.values[name.lexeme]
+        except IndexError:
+            if self.enclosing is not None:
+                return self.enclosing.get(name)
+            raise PebbleRuntimeError(name, f"Undefined variable '{name.lexeme}'.")
+
+    def assign(self, name: Token, value: Any):
+        if name.lexeme not in self.values:
+            if self.enclosing is not None:
+                self.enclosing.assign(name, value)
+                return
+            raise PebbleRuntimeError(name, f"Undefined variable '{name.lexeme}'.")
+        self.values[name.lexeme] = value
+
+    def clear(self):
+        self.values = {}

src/interpreter/interpreter.py

@@ -1,36 +1,16 @@
 from typing import Any
 
 from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr
-from src.ast.stmt import Stmt, PrintStmt, T, ExpressionStmt, LetStmt
+from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt
+from src.interpreter.environment import Environment
 from src.interpreter.error import PebbleRuntimeError
 from src.pebble import Pebble
 from src.token import TokenType, Token
 
 
 class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
-    class Environment:
-        def __init__(self):
-            self.values: dict[str, Any] = {}
-
-        def define(self, name: str, value: Any):
-            self.values[name] = value
-
-        def get(self, name: Token) -> Any:
-            try:
-                return self.values[name.lexeme]
-            except IndexError:
-                raise PebbleRuntimeError(name, f"Undefined variable '{name.lexeme}'.")
-
-        def assign(self, name: Token, value: Any):
-            if name.lexeme not in self.values:
-                raise PebbleRuntimeError(name, f"Undefined variable '{name.lexeme}'.")
-            self.values[name.lexeme] = value
-
-        def clear(self):
-            self.values = {}
-
     def __init__(self):
-        self.env: Interpreter.Environment = Interpreter.Environment()
+        self.env: Environment = Environment()
 
     def interpret(self, statements: list[Stmt]) -> None:
         self.env.clear()