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
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157

use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, LinkedList, VecDeque};
use std::hash::{BuildHasher, Hash};

use higher::Lift;

/// `Bind` lets you chain computations together.
///
/// It takes a function `Fn(A) -> M<B>` and applies it to the `A` inside `M<A>`.
/// You can think of this as a callback function for when the value of `A` is
/// ready to be processed, returning the next computation in the sequence.
pub trait Bind<A, B>: Lift<A, B> {
    /// Use the value inside an `M<A>: Bind` to create an `M<B>`.
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1;
}

impl<A, B> Bind<A, B> for Option<A> {
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.and_then(f)
    }
}

impl<A, B, E> Bind<A, B> for Result<A, E> {
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.and_then(f)
    }
}

impl<A, B> Bind<A, B> for Vec<A> {
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B> Bind<A, B> for VecDeque<A> {
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B> Bind<A, B> for LinkedList<A> {
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B> Bind<A, B> for BinaryHeap<A>
where
    A: Ord,
    B: Ord,
{
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B> Bind<A, B> for BTreeSet<A>
where
    A: Ord,
    B: Ord,
{
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B, S> Bind<A, B> for HashSet<A, S>
where
    A: Hash + Eq,
    B: Hash + Eq,
    S: BuildHasher + Default,
{
    fn bind<F>(self, f: F) -> <Self as Lift<A, B>>::Target1
    where
        F: Fn(A) -> <Self as Lift<A, B>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B, C, D, S> Bind<(A, B), (C, D)> for HashMap<A, B, S>
where
    A: Hash + Eq,
    B: Hash + Eq,
    C: Hash + Eq,
    D: Hash + Eq,
    S: BuildHasher + Default,
{
    fn bind<F>(self, f: F) -> <Self as Lift<(A, B), (C, D)>>::Target1
    where
        F: Fn((A, B)) -> <Self as Lift<(A, B), (C, D)>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

impl<A, B, C, D> Bind<(A, B), (C, D)> for BTreeMap<A, B>
where
    A: Ord,
    B: Ord,
    C: Ord,
    D: Ord,
{
    fn bind<F>(self, f: F) -> <Self as Lift<(A, B), (C, D)>>::Target1
    where
        F: Fn((A, B)) -> <Self as Lift<(A, B), (C, D)>>::Target1,
    {
        self.into_iter().flat_map(|v| f(v).into_iter()).collect()
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::Pure;
    use proptest::collection::vec;
    use proptest::num::u8;
    use proptest::proptest;

    #[test]
    fn bind_vec() {
        let v = vec![1, 2, 3];
        let o = v.bind(|i| vec![i, i + 1]);
        assert_eq!(vec![1, 2, 2, 3, 3, 4], o);
    }

    proptest! {
        #[test]
        fn identity(v in vec(u8::ANY, 0..1000)) {
            let orig = v.clone();
            let result = v.bind(Pure::pure);
            assert_eq!(orig, result);
        }
    }
}