New in version 2.0.
Iterate leaf pairs forward in expr:
abjad> score = Score([])
abjad> notes = [Note("c'8"), Note("d'8"), Note("e'8"), Note("f'8"), Note("g'4")]
abjad> score.append(Staff(notes))
abjad> notes = [Note(x, (1, 4)) for x in [-12, -15, -17]]
abjad> score.append(Staff(notes))
abjad> contexttools.ClefMark('bass')(score[1])
ClefMark('bass')(Staff{3})
abjad> f(score)
\new Score <<
\new Staff {
c'8
d'8
e'8
f'8
g'4
}
\new Staff {
\clef "bass"
c4
a,4
g,4
}
>>
abjad> for pair in leaftools.iterate_leaf_pairs_forward_in_expr(score):
... pair
(Note("c'8"), Note('c4'))
(Note("c'8"), Note("d'8"))
(Note('c4'), Note("d'8"))
(Note("d'8"), Note("e'8"))
(Note("d'8"), Note('a,4'))
(Note('c4'), Note("e'8"))
(Note('c4'), Note('a,4'))
(Note("e'8"), Note('a,4'))
(Note("e'8"), Note("f'8"))
(Note('a,4'), Note("f'8"))
(Note("f'8"), Note("g'4"))
(Note("f'8"), Note('g,4'))
(Note('a,4'), Note("g'4"))
(Note('a,4'), Note('g,4'))
(Note("g'4"), Note('g,4'))
Iterate leaf pairs left-to-right and top-to-bottom.
Return generator.