MPIX_Op_create_x:
    user_fn_x: FUNCTION, func_type=MPIX_User_function_x, [user defined function with extra_state]
    destructor_fn: FUNCTION, func_type=MPIX_Destructor_function, [callback when op is freed]
    commute: LOGICAL, suppress=lis_paren, [true if commutative; false otherwise.]
    extra_state: EXTRA_STATE, [extra state]
    op: OPERATION, direction=out, [operation]
    .desc: Creates a user-defined reduction op with an extra_state
/*
    Notes on MPIX_User_function_x:
    The calling list for the user function type is
    .vb
        typedef void (MPIX_User_function_x) (void * a, void * b,
                                             MPI_Count len, MPI_Datatype datatype,
                                             void *extra_state);
    .ve
    There are a few differences from MPI_User_function used in MPI_Op_create.
    1. It passes len and datatype as scalar input, rather than as addresses.
    2. The len is of MPI_Count, rather than int.
    3. It accepts a void *extra_state which is passed from users during MPIX_Op_create_x.
*/

MPIX_Comm_create_errhandler_x:
    comm_errhandler_fn_x: FUNCTION, func_type=MPIX_Comm_errhandler_function_x, [user defined error handling procedure with extra_state]
    destructor_fn: FUNCTION, func_type=MPIX_Destructor_function, [callback when op is freed]
    extra_state: EXTRA_STATE, [extra state]
    errhandler: ERRHANDLER, direction=out
    .desc: Creates an MPI-style communicator errorhandler with an extra_state

MPIX_Win_create_errhandler_x:
    comm_errhandler_fn_x: FUNCTION, func_type=MPIX_Win_errhandler_function_x, [user defined error handling procedure with extra_state]
    destructor_fn: FUNCTION, func_type=MPIX_Destructor_function, [callback when op is freed]
    extra_state: EXTRA_STATE, [extra state]
    errhandler: ERRHANDLER, direction=out
    .desc: Creates an MPI-style window errorhandler with an extra_state

MPIX_File_create_errhandler_x:
    comm_errhandler_fn_x: FUNCTION, func_type=MPIX_File_errhandler_function_x, [user defined error handling procedure with extra_state]
    destructor_fn: FUNCTION, func_type=MPIX_Destructor_function, [callback when op is freed]
    extra_state: EXTRA_STATE, [extra state]
    errhandler: ERRHANDLER, direction=out
    .desc: Creates an MPI-style file errorhandler with an extra_state

MPIX_Session_create_errhandler_x:
    comm_errhandler_fn_x: FUNCTION, func_type=MPIX_Session_errhandler_function_x, [user defined error handling procedure with extra_state]
    destructor_fn: FUNCTION, func_type=MPIX_Destructor_function, [callback when op is freed]
    extra_state: EXTRA_STATE, [extra state]
    errhandler: ERRHANDLER, direction=out
    .desc: Creates an MPI-style session errorhandler with an extra_state