ascent 0.8.0

Logic programming in Rust
Documentation 
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

//! Binding `let` clause

use ascent::ascent;

#[derive(Clone, Eq, PartialEq, Hash, Debug)]
pub enum List {
   Nil,
   Cons(usize, Box<List>),
}

impl List {
   fn as_vec(&self) -> Vec<usize> {
      let mut items = vec![];

      let mut list = self;
      while let Self::Cons(head, tail) = list {
         items.push(*head);
         list = tail;
      }

      items
   }
}

ascent! {
    // Rules:

    relation list(List, usize);

    list(List::Nil, 0);
    list(List::Cons(*l, Box::new(t.clone())), h) <-- list(t, l), let h = *l + 1, if h <= 5;
}

fn main() {
   let mut prog = AscentProgram::default();

   prog.run();

   let AscentProgram { mut list, .. } = prog;

   list.sort_by_key(|(_, key)| *key);

   let lists: Vec<_> = list.into_iter().map(|(list, len)| (list.as_vec(), len)).collect();

   assert_eq!(lists, vec![
      (vec![], 0),
      (vec![0], 1),
      (vec![1, 0], 2),
      (vec![2, 1, 0], 3),
      (vec![3, 2, 1, 0], 4),
      (vec![4, 3, 2, 1, 0], 5),
   ]);
}