New in version 2.6.
True when expr is a sequence of Abjad pitch arrays:
abjad> from abjad.tools import pitcharraytools
abjad> pitch_array = pitcharraytools.PitchArray([[1, 2, 1], [2, 1, 1]])
abjad> pitcharraytools.all_are_pitch_arrays([pitch_array])
True
True when expr is an empty sequence:
abjad> pitcharraytools.all_are_pitch_arrays([])
True
Otherwise false:
abjad> pitcharraytools.all_are_pitch_arrays('foo')
False
Return boolean.