Don't deadlock during nested evaluation in print context

Lock for stdout should only hold when things are ready to be printed.
This prevents any double locking issues

musique/main.cc

@@ -191,12 +191,19 @@ struct Runner
 
 		Env::global->force_define("print", +[](Interpreter &interpreter, std::vector<Value> args) -> Result<Value> {
 			static std::mutex stdio_mutex;
-			std::lock_guard guard{stdio_mutex};
 			for (auto it = args.begin(); it != args.end(); ++it) {
-				std::cout << Try(format(interpreter, *it));
-				if (std::next(it) != args.end())
+				{
+					auto result = Try(format(interpreter, *it));
+					std::lock_guard guard{stdio_mutex};
+					std::cout << result;
+				}
+
+				if (std::next(it) != args.end()) {
+					std::lock_guard guard{stdio_mutex};
 					std::cout << ' ';
+				}
 			}
+			std::lock_guard guard{stdio_mutex};
 			std::cout << std::endl;
 			return {};
 		});