challenge 7.2 done

pylox/cli.py

@@ -50,22 +50,12 @@ def run(self, src: str) -> None:
             tokens = Scanner(src).scan_tokens()
             ast = Parser(tokens, self.report_error).parse()
             if ast is not None:
-                print(self.stringify(self.interpreter.evaluate(ast)))
+                print(self.interpreter.interpret(ast))
         except LoxSyntaxError as e:
             self.report_error(e)
         except LoxRuntimeError as e:
             self.report_runtime_error(e)
 
-    @staticmethod
-    def stringify(value: typing.Any) -> str:
-        if value is None:
-            return "nil"
-
-        if type(value) is float and float(value).is_integer():
-            return str(int(value))
-
-        return str(value)
-
     @staticmethod
     def _build_error_string(err: LoxException) -> str:
         return f"{err.line + 1}: [bold red]{err.message}[/bold red]"

pylox/interpreter.py

@@ -6,6 +6,9 @@
 
 
 class Interpreter(ast.ExprVisitor):
+    def interpret(self, expr: ast.Expr):
+        return self.stringify(self.evaluate(expr))
+
     def evaluate(self, expr: ast.Expr) -> typing.Any:
         return expr.accept(self)
 
@@ -40,9 +43,12 @@ def visit_binary_expr(self, expr: ast.Binary):
                 if type(left) is str and type(right) is str:
                     return left + right
 
+                if type(left) is str or type(right) is str:
+                    return str(left) + str(right)
+
                 raise LoxRuntimeError(
                     expr.operator,
-                    "Operands must be two numbers of two strings.",
+                    "Operands must be numbers or strings.",
                 )
             case TokenType.SLASH:
                 self.check_number_operands(expr.operator, left, right)
@@ -96,3 +102,13 @@ def check_number_operands(op: Token, left, right: typing.Any) -> None:
         if Interpreter.is_number(left) and Interpreter.is_number(right):
             return
         raise LoxRuntimeError(op, "Operands must be a numbers.")
+
+    @staticmethod
+    def stringify(value: typing.Any) -> str:
+        if value is None:
+            return "nil"
+
+        if type(value) is float and float(value).is_integer():
+            return str(int(value))
+
+        return str(value)