feat: add logical expressions

examples/09_logical.peb

@@ -0,0 +1,2 @@
+print("hi" or 2) // "hi".
+print(null or "yes") // "yes".

main.py

@@ -13,7 +13,7 @@ def main():
     123
     "This is
      another string" """
-    path: str = "examples/04_if_else.peb"
+    path: str = "examples/09_logical.peb"
     with open(path, "r") as f:
         source = f.read()
     lexer: Lexer = Lexer()

src/ast/expr.py

@@ -41,6 +41,10 @@ class Expr(ABC):
         def visit_variable_expr(self, expr: VariableExpr) -> T:
             ...
 
+        @abstractmethod
+        def visit_logical_expr(self, expr: LogicalExpr) -> T:
+            ...
+
 
 @dataclass(frozen=True)
 class AssignExpr(Expr):
@@ -92,3 +96,13 @@ class VariableExpr(Expr):
 
     def accept(self, visitor: Expr.Visitor[T]) -> T:
         return visitor.visit_variable_expr(self)
+
+
+@dataclass(frozen=True)
+class LogicalExpr(Expr):
+    left: Expr
+    operator: Token
+    right: Expr
+
+    def accept(self, visitor: Expr.Visitor[T]) -> T:
+        return visitor.visit_logical_expr(self)

src/interpreter/interpreter.py

@@ -1,6 +1,6 @@
 from typing import Any
 
-from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr
+from src.ast.expr import LiteralExpr, GroupingExpr, UnaryExpr, BinaryExpr, Expr, VariableExpr, AssignExpr, LogicalExpr
 from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt
 from src.interpreter.environment import Environment
 from src.interpreter.error import PebbleRuntimeError
@@ -40,6 +40,21 @@ class Interpreter(Expr.Visitor[Any], Stmt.Visitor[None]):
         self.env.assign(expr.name, value)
         return value
 
+    def visit_logical_expr(self, expr: LogicalExpr) -> Any:
+        left: Any = self.evaluate(expr.left)
+
+        match expr.operator.type:
+            case TokenType.OR:
+                if self.is_truthy(left):
+                    return left
+            case TokenType.AND:
+                if not self.is_truthy(left):
+                    return left
+            case _:
+                # Unreachable
+                raise PebbleRuntimeError(expr.operator, f"Unknown logical operator")
+        return self.evaluate(expr.right)
+
     def visit_binary_expr(self, expr: BinaryExpr) -> Any:
         left: Any = self.evaluate(expr.left)
         right: Any = self.evaluate(expr.right)

src/parser/parser.py

@@ -1,6 +1,6 @@
 from typing import Optional
 
-from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr, AssignExpr
+from src.ast.expr import Expr, BinaryExpr, UnaryExpr, LiteralExpr, GroupingExpr, VariableExpr, AssignExpr, LogicalExpr
 from src.ast.stmt import Stmt, PrintStmt, ExpressionStmt, LetStmt, BlockStmt, IfStmt
 from src.parser.error import ParsingError
 from src.pebble import Pebble
@@ -149,7 +149,7 @@ class Parser:
         return self.assignment()
 
     def assignment(self) -> Expr:
-        expr: Expr = self.equality()
+        expr: Expr = self.or_()
         if self.match(TokenType.EQUAL, TokenType.PLUS_EQUAL, TokenType.MINUS_EQUAL, TokenType.STAR_EQUAL, TokenType.SLASH_EQUAL):
             operator: Token = self.previous()
             value: Expr = self.assignment()
@@ -169,6 +169,22 @@ class Parser:
             self.error(operator, "Invalid assignment target.")
         return expr
 
+    def or_(self) -> Expr:
+        expr: Expr = self.and_()
+        while self.match(TokenType.OR):
+            operator: Token = self.previous()
+            right: Expr = self.and_()
+            expr = LogicalExpr(expr, operator, right)
+        return expr
+
+    def and_(self) -> Expr:
+        expr: Expr = self.equality()
+        while self.match(TokenType.AND):
+            operator: Token = self.previous()
+            right: Expr = self.equality()
+            expr = LogicalExpr(expr, operator, right)
+        return expr
+
     def equality(self) -> Expr:
         expr: Expr = self.comparison()
         while self.match(TokenType.BANG_EQUAL, TokenType.EQUAL_EQUAL):