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
#[macro_export]
macro_rules! monadic {
(pure $e:expr ) => [Some($e)];
(let $v:ident = $e:expr ; $($rest:tt)*) => [Some($e).into_iter().flat_map( move |$v| { monadic!($($rest)*)} )];
(guard $boolean:expr ; $($rest:tt)*) => [(if $boolean {Some(())} else {None}).into_iter().flat_map( move |_| { monadic!($($rest)*)} )];
(_ <- $monad:expr ; $($rest:tt)* ) => [($monad).into_iter().flat_map( move |_| { monadic!($($rest)*)} )];
(&$v:ident <- $monad:expr ; $($rest:tt)* ) => [($monad).into_iter().flat_map( move |&$v| { monadic!($($rest)*)} )];
($v:ident <- pure $e:expr ; $($rest:tt)* ) => [Some($e).into_iter().flat_map( move |$v| { monadic!($($rest)*)} )];
($v:ident <- $monad:expr ; $($rest:tt)* ) => [($monad).into_iter().flat_map( move |$v| { monadic!($($rest)*)} )];
($monad:expr ) => [$monad];
}
#[cfg(test)]
mod tests {
#[test]
fn it_works() {
let xs = (1..6).collect::<Vec<i32>>();
let zs = (&xs).into_iter().filter(|&v| v < &4).map(|v| v*2).collect::<Vec<i32>>();
let ys = monadic!{
&v <- &xs;
guard v < 4;
pure v * 2
}.collect::<Vec<i32>>();
assert_eq!(ys, zs);
}
}