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
use std::marker::PhantomData;
use std::{fmt, hash};
#[macro_use]
pub mod lift;
pub trait Identity<A: ?Sized, B: ?Sized>: Sized {
type Inverse: Identity<B, A, Inverse = Self>;
fn conv(&self, x: A) -> B where A: Sized, B: Sized;
fn conv_ref<'a>(&self, x: &'a A) -> &'a B;
fn conv_mut<'a>(&self, x: &'a mut A) -> &'a mut B;
fn conv_box(&self, x: Box<A>) -> Box<B>;
fn conv_under<TF: lift::TyFun<A> + lift::TyFun<B>>(&self, x: <TF as lift::TyFun<A>>::Result) -> <TF as lift::TyFun<B>>::Result
where <TF as lift::TyFun<A>>::Result: Sized, <TF as lift::TyFun<B>>::Result: Sized;
fn inv(&self) -> &Self::Inverse;
fn elim<Prop: lift::TyFun2<A, Refl<A>> + lift::TyFun2<B, Self>>
(&self, refl_case: <Prop as lift::TyFun2<A, Refl<A>>>::Result) -> <Prop as lift::TyFun2<B, Self>>::Result
where <Prop as lift::TyFun2<A, Refl<A>>>::Result: Sized, <Prop as lift::TyFun2<B, Self>>::Result: Sized;
}
pub fn refl<A: ?Sized>() -> Refl<A> { Refl::default() }
pub struct Refl<A: ?Sized> {
phantom_fn: PhantomData<fn(A) -> A>,
}
impl<A: ?Sized> fmt::Debug for Refl<A> {
fn fmt(&self, fmtr: &mut fmt::Formatter) -> fmt::Result { fmtr.debug_struct("Refl").field("phantom_fn", &self.phantom_fn).finish() }
}
impl<A: ?Sized> Clone for Refl<A> {
fn clone(&self) -> Refl<A> { refl() }
}
impl<A: ?Sized> Copy for Refl<A> {}
impl<A: ?Sized> Default for Refl<A> {
fn default() -> Refl<A> { Refl { phantom_fn: PhantomData } }
}
impl<A: ?Sized> hash::Hash for Refl<A> {
fn hash<H: hash::Hasher>(&self, hshr: &mut H) { self.phantom_fn.hash(hshr); }
}
impl<A: ?Sized> Identity<A, A> for Refl<A> {
type Inverse = Self;
fn conv(&self, x: A) -> A
where A: Sized {
x
}
fn conv_ref<'a>(&self, x: &'a A) -> &'a A { x }
fn conv_mut<'a>(&self, x: &'a mut A) -> &'a mut A { x }
fn conv_box(&self, x: Box<A>) -> Box<A> { x }
fn inv(&self) -> &Self { self }
fn conv_under<TF: lift::TyFun<A>>(&self, x: TF::Result) -> TF::Result
where TF::Result: Sized {
x
}
fn elim<Prop: lift::TyFun2<A, Refl<A>>>(&self,
refl_case: <Prop as lift::TyFun2<A, Refl<A>>>::Result)
-> <Prop as lift::TyFun2<A, Refl<A>>>::Result
where <Prop as lift::TyFun2<A, Refl<A>>>::Result: Sized {
refl_case
}
}
pub trait Equals<Other: ?Sized> {
type IdentityWitness: Identity<Self, Other>;
fn identity_witness() -> Self::IdentityWitness;
}
impl<T: ?Sized> Equals<T> for T {
type IdentityWitness = Refl<T>;
fn identity_witness() -> Refl<T> { refl() }
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn inv_conv_test() {
fn inv_conv<A, B, Ev: Identity<A, B>>(ev: Ev, x: B) -> A { ev.inv().conv(x) }
assert_eq!(inv_conv(Refl::default(), 0), 0)
}
}