New in version 2.6.
True when expr is a sequence of Abjad leaves:
abjad> leaves = [Note("c'4"), Rest('r4'), Note("d'4")]
abjad> leaftools.all_are_leaves(leaves)
True
True when expr is an empty sequence:
abjad> leaftools.all_are_leaves([])
True
Otherwise false:
abjad> leaftools.all_are_leaves('foo')
False
Return boolean.
Function wraps componenttools.all_are_components().