function ARG_PASS_RETURN, arg
  return, arg
end

>>> import GDL
>>> import numpy
>>> arg = numpy.arange(0, 259, dtype=int)
>>> retval = GDL.function('arg_pass_return', arg)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
GDL.error: Calling ARG_PASS_RETURN: FromPython: Unknown array type.
>>> arg = numpy.arange(-255, 255, dtype=numpy.int8)
>>> retval = GDL.function('arg_pass_return', arg)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
GDL.error: Calling ARG_PASS_RETURN: FromPython: Unknown array type.