feat: add block statements and scoped environment

examples/08_scopes.peb

@@ -0,0 +1,19 @@
+let a = "global a"
+let b = "global b"
+let c = "global c"
+{
+  let a = "outer a"
+  let b = "outer b"
+  {
+    let a = "inner a"
+    print(a)
+    print(b)
+    print(c)
+  }
+  print(a)
+  print(b)
+  print(c)
+}
+print(a)
+print(b)
+print(c)

main.py

@@ -13,7 +13,7 @@ def main():
     123
     "This is
      another string" """
-    path: str = "examples/01_variables.peb"
+    path: str = "examples/08_scopes.peb"
     with open(path, "r") as f:
         source = f.read()
     lexer: Lexer = Lexer()

src/ast/stmt.py

@@ -17,6 +17,10 @@ class Stmt(ABC):
         ...
 
     class Visitor(ABC, Generic[T]):
+        @abstractmethod
+        def visit_block_stmt(self, stmt: BlockStmt) -> T:
+            ...
+
         @abstractmethod
         def visit_expression_stmt(self, stmt: ExpressionStmt) -> T:
             ...
@@ -30,6 +34,14 @@ class Stmt(ABC):
             ...
 
 
+@dataclass(frozen=True)
+class BlockStmt(Stmt):
+    statements: list[Stmt]
+
+    def accept(self, visitor: Stmt.Visitor[T]) -> T:
+        return visitor.visit_block_stmt(self)
+
+
 @dataclass(frozen=True)
 class ExpressionStmt(Stmt):
     expression: Expr

src/interpreter/interpreter.py

@@ -1,7 +1,7 @@
 from typing import Any
 
 from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr
-from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt
+from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt
 from src.interpreter.environment import Environment
 from src.interpreter.error import PebbleRuntimeError
 from src.pebble import Pebble
@@ -26,6 +26,15 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
     def execute(self, stmt: Stmt) -> None:
         stmt.accept(self)
 
+    def execute_block(self, statements: list[Stmt], env: Environment) -> None:
+        previous_env: Environment = self.env
+        try:
+            self.env = env
+            for stmt in statements:
+                self.execute(stmt)
+        finally:
+            self.env = previous_env
+
     def visit_assign_expr(self, expr: AssignExpr) -> Any:
         value: Any = self.evaluate(expr.value)
         self.env.assign(expr.name, value)
@@ -93,6 +102,9 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
     def visit_variable_expr(self, expr: VariableExpr) -> Any:
         return self.env.get(expr.name)
 
+    def visit_block_stmt(self, stmt: BlockStmt) -> None:
+        self.execute_block(stmt.statements, Environment(self.env))
+
     def visit_expression_stmt(self, stmt: ExpressionStmt) -> None:
         self.evaluate(stmt.expression)
 

src/parser/parser.py

@@ -1,7 +1,7 @@
 from typing import Optional
 
 from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr, AssignExpr
-from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt
+from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt
 from src.parser.error import ParsingError
 from src.pebble import Pebble
 from src.token import Token, TokenType
@@ -109,6 +109,8 @@ class Parser:
     def statement(self) -> Stmt:
         if self.match(TokenType.PRINT):
             return self.print_stmt()
+        if self.match(TokenType.LEFT_BRACE):
+            return self.block_stmt()
         return self.expression_stmt()
 
     def print_stmt(self) -> Stmt:
@@ -118,6 +120,16 @@ class Parser:
         self.expect_eol("Expected end of line after statement")
         return PrintStmt(value)
 
+    def block_stmt(self) -> Stmt:
+        statements: list[Stmt] = []
+        self.skip_newlines()
+        while not self.check(TokenType.RIGHT_BRACE) and not self.is_at_end():
+            self.skip_newlines()
+            statements.append(self.declaration())
+
+        self.consume(TokenType.RIGHT_BRACE, "Expected '}' after block.")
+        return BlockStmt(statements)
+
     def expression_stmt(self) -> Stmt:
         value: Expr = self.expression()
         self.expect_eol("Expected end of line after expression")