(lldb) th backtrace * thread #3, queue = 'com.apple.root.default-qos', stop reason = breakpoint 1.1 frame #0: 0x000000010e89e001 libobjc.A.dylib`objc_exception_throw frame #1: 0x000000010f2090b9 CoreFoundation`-[NSException raise] + 9 * frame #2: 0x000000010df90ea6 StackChain`doInnerSomething() at ViewController.swift:8 frame #3: 0x000000010df90e19 StackChain`doSomething() at ViewController.swift:4 frame #4: 0x000000010df910c9 StackChain`closure #1 in ViewController.onButton() at ViewController.swift:14 frame #5: 0x000000010df910fd StackChain`thunk for @escaping @callee_guaranteed () -> () at ViewController.swift:0 frame #6: 0x000000011359b7ab libdispatch.dylib`_dispatch_call_block_and_release + 12 frame #7: 0x000000011359c7ec libdispatch.dylib`_dispatch_client_callout + 8 frame #8: 0x00000001135a1619 libdispatch.dylib`_dispatch_queue_override_invoke + 1451 frame #9: 0x00000001135a836c libdispatch.dylib`_dispatch_root_queue_drain + 664 frame #10: 0x00000001135a8076 libdispatch.dylib`_dispatch_worker_thread3 + 132 frame #11: 0x0000000113ac7169 libsystem_pthread.dylib`_pthread_wqthread + 1387 frame #12: 0x0000000113ac6be9 libsystem_pthread.dylib`start_wqthread + 13 (lldb)