functor 0.1.2

Covariant, contravariant, invariant and bivariant functors.
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
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

pub mod isomorphism;
pub mod parametric;

use isomorphism::{Iso, IsoOnce};
use parametric::{Param, ReParam};

pub trait Covariant<'a, B>: ReParam<B> {
    fn fmap<F: 'a + Fn(Self::Param) -> B>(self, F) -> Self::Output;
}

pub trait CovariantOnce<'a, B>: ReParam<B> + Covariant<'a, B> {
    fn fmap_once<F: 'a + FnOnce(Self::Param) -> B>(self, F) -> Self::Output;
}

pub trait Contravariant<'a, B>: ReParam<B> {
    fn contramap<F: 'a + Fn(B) -> Self::Param>(self, F) -> Self::Output;
}

pub trait ContravariantOnce<'a, B>: ReParam<B> + Contravariant<'a, B> {
    fn contramap_once<F: 'a + FnOnce(B) -> Self::Param>(self, F) -> Self::Output;
}

pub trait Invariant<'a, B>: ReParam<B> {
    fn invmap<F: 'a + Iso<Self::Param, B>>(self, F) -> Self::Output;
}

pub trait InvariantOnce<'a, B>: ReParam<B> + Invariant<'a, B> {
    fn invmap_once<F: 'a + IsoOnce<Self::Param, B>>(self, F) -> Self::Output;
}

pub trait Bivariant<'a, B>: ReParam<B> {
    fn xmap(self) -> Self::Output;
}

pub trait NaturalTransform<T: Param<Param=Self::Param>>: Param {
    fn transform(self) -> T;
}

impl<'a, A, B> Covariant<'a, B> for std::option::Option<A> {
    fn fmap<F: 'a + Fn(A) -> B>(self, f: F) -> Self::Output {
        self.fmap_once(f)
    }
}

impl<'a, A, B> CovariantOnce<'a, B> for std::option::Option<A> {
    fn fmap_once<F: 'a + FnOnce(A) -> B>(self, f: F) -> Self::Output {
        self.map(|a| f(a))
    }
}

impl<'a, X, A, B> Covariant<'a, B> for (X, A) {
    fn fmap<F: Fn(A) -> B>(self, f: F) -> Self::Output {
        self.fmap_once(f)
    }
}

impl<'a, X, A, B> CovariantOnce<'a, B> for (X, A) {
    fn fmap_once<F: FnOnce(A) -> B>(self, f: F) -> Self::Output {
        (self.0, f(self.1))
    }
}

impl<'a, A, B> Covariant<'a, B> for Box<A> {
    fn fmap<F: 'a + Fn(A) -> B>(self, f: F) -> Self::Output {
        self.fmap_once(f)
    }
}

impl<'a, A, B> CovariantOnce<'a, B> for Box<A> {
    fn fmap_once<F: FnOnce(A) -> B>(self, f: F) -> Self::Output {
        Box::new(f(*self))
    }
}

impl<'a, A, B, E> Covariant<'a, B> for Result<A, E> {
    fn fmap<F: 'a + Fn(A) -> B>(self, f: F) -> Self::Output {
        self.fmap_once(f)
    }
}

impl<'a, A, B, E> CovariantOnce<'a, B> for Result<A, E> {
    fn fmap_once<F: FnOnce(A) -> B>(self, f: F) -> Self::Output {
        self.map(f)
    }
}

impl<'a, A, B> Bivariant<'a, B> for std::marker::PhantomData<A> {
    fn xmap(self) -> Self::Output { std::marker::PhantomData }
}

impl<A> NaturalTransform<Option<A>> for Box<A> {
    fn transform(self) -> Option<A> {
        Option::Some(*self)
    }
}

impl<A, E> NaturalTransform<Option<A>> for Result<A, E> {
    fn transform(self) -> Option<A> {
        self.ok()
    }
}

#[test]
fn it_works() {
}