A classic one; Microsoft's three value BOOL: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getmessage https://docs.microsoft.com/en-us/w

A classic one; Microsoft's three value BOOL: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getmessage https://docs.microsoft.com/en-us/windows/win32/api/winuser/n... Can return -1, FALSE and TRUE.