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
|
use dhall_syntax::{Label, V};
/// Stores a pair of variables: a normal one and if relevant one
/// that corresponds to the alpha-normalized version of the first one.
/// Equality is up to alpha-equivalence.
#[derive(Debug, Clone, Eq)]
pub(crate) struct AlphaVar {
normal: V<Label>,
alpha: Option<V<()>>,
}
// Exactly like a Label, but equality returns always true.
// This is so that Value equality is exactly alpha-equivalence.
#[derive(Debug, Clone, Eq)]
pub(crate) struct AlphaLabel(Label);
pub(crate) trait Shift {
fn shift(&self, delta: isize, var: &AlphaVar) -> Self;
}
pub(crate) trait Subst<T>: Shift {
fn subst_shift(&self, var: &AlphaVar, val: &T) -> Self;
}
impl AlphaVar {
pub(crate) fn to_var(&self, alpha: bool) -> V<Label> {
match (alpha, &self.alpha) {
(true, Some(x)) => V("_".into(), x.1),
_ => self.normal.clone(),
}
}
pub(crate) fn from_var(normal: V<Label>) -> Self {
AlphaVar {
normal,
alpha: None,
}
}
}
impl AlphaLabel {
pub(crate) fn to_label_maybe_alpha(&self, alpha: bool) -> Label {
if alpha {
"_".into()
} else {
self.to_label()
}
}
pub(crate) fn to_label(&self) -> Label {
self.clone().into()
}
}
impl Shift for AlphaVar {
fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
AlphaVar {
normal: self.normal.shift(delta, &var.normal),
alpha: match (&self.alpha, &var.alpha) {
(Some(x), Some(v)) => Some(x.shift(delta, v)),
_ => None,
},
}
}
}
impl std::cmp::PartialEq for AlphaVar {
fn eq(&self, other: &Self) -> bool {
match (&self.alpha, &other.alpha) {
(Some(x), Some(y)) => x == y,
(None, None) => self.normal == other.normal,
_ => false,
}
}
}
impl std::cmp::PartialEq for AlphaLabel {
fn eq(&self, _other: &Self) -> bool {
true
}
}
impl From<Label> for AlphaVar {
fn from(x: Label) -> AlphaVar {
AlphaVar {
normal: V(x, 0),
alpha: Some(V((), 0)),
}
}
}
impl<'a> From<&'a Label> for AlphaVar {
fn from(x: &'a Label) -> AlphaVar {
x.clone().into()
}
}
impl From<AlphaLabel> for AlphaVar {
fn from(x: AlphaLabel) -> AlphaVar {
let l: Label = x.into();
l.into()
}
}
impl<'a> From<&'a AlphaLabel> for AlphaVar {
fn from(x: &'a AlphaLabel) -> AlphaVar {
x.clone().into()
}
}
impl From<Label> for AlphaLabel {
fn from(x: Label) -> AlphaLabel {
AlphaLabel(x)
}
}
impl From<AlphaLabel> for Label {
fn from(x: AlphaLabel) -> Label {
x.0
}
}
|
