1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
use {List, Queue};
#[cfg(not(feature="nightly"))]
use HetFnMut as FnMut;
pub trait Foldable<I, F> {
fn fold(self, init: I, f: F) -> I;
}
impl<I, F> Foldable<I, F> for List<()> {
fn fold(self, init: I, _: F) -> I { init }
}
impl<I, F> Foldable<I, F> for Queue<()> {
fn fold(self, init: I, _: F) -> I { init }
}
impl<I, F, H, T> Foldable<I, F> for List<(H, T)>
where T: Foldable<I, F>,
F: FnMut<(H, I), Output=I>
{
fn fold(self, init: I, mut f: F) -> I {
let List((head, tail)) = self;
tail.fold(f.call_mut((head, init)), f)
}
}
impl<I, F, H, T> Foldable<I, F> for Queue<(H, T)>
where H: for<'a> Foldable<I, &'a mut F>,
F: FnMut<(T, I), Output=I>
{
fn fold(self, init: I, mut f: F) -> I {
let Queue((head, tail)) = self;
let head = head.fold(init, &mut f);
f.call_mut((tail, head))
}
}