evaltrees 0.1.0

A simple term-rewriting interpreter that displays intermediate expressions.
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
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
158
159
160
161

use linked_hash_set::LinkedHashSet;

use ast::{Decl, Expr, Pattern, Type};
use typeck::{subst::SubstVar, ty::Ty, util::UnreifyEnv};

// TODO: This reification is unsound in the presence of higher rank polymorphism.

impl Decl<Ty> {
    /// Reifies a declaration.
    pub(in typeck) fn reify(self) -> Decl<Type> {
        let mut vars = LinkedHashSet::new();
        for arg in &self.args {
            arg.collect_vars(&mut vars);
        }
        self.body.collect_vars(&mut vars);

        let env = vars.into_iter().rev().collect::<Vec<_>>();
        let mut ty = self.aux.reify_in(&env);
        for _ in &env {
            ty = Type::Forall(Box::new(ty));
        }

        let args = self.args
            .into_iter()
            .map(|arg| arg.reify_in(&env))
            .collect();
        let body = self.body.reify_in(&env);
        Decl {
            name: self.name,
            args,
            body,
            aux: ty,
        }
    }
}

impl Expr<Ty> {
    fn collect_vars(&self, vars: &mut LinkedHashSet<SubstVar>) {
        match *self {
            Expr::If(ref c, ref t, ref e, ref ty) => {
                c.collect_vars(vars);
                t.collect_vars(vars);
                e.collect_vars(vars);
                ty.collect_vars(vars);
            }
            Expr::Literal(_, ref ty) | Expr::Variable(_, ref ty) => {
                ty.collect_vars(vars);
            }
            Expr::Op(_, ref l, ref r, ref ty) => {
                l.collect_vars(vars);
                r.collect_vars(vars);
                ty.collect_vars(vars);
            }
        }
    }

    fn reify_in(self, env: &[SubstVar]) -> Expr<Type> {
        match self {
            Expr::If(c, t, e, ty) => Expr::If(
                Box::new(c.reify_in(env)),
                Box::new(t.reify_in(env)),
                Box::new(e.reify_in(env)),
                ty.reify_in(env),
            ),
            Expr::Literal(l, ty) => Expr::Literal(l, ty.reify_in(env)),
            Expr::Op(o, l, r, ty) => Expr::Op(
                o,
                Box::new(l.reify_in(env)),
                Box::new(r.reify_in(env)),
                ty.reify_in(env),
            ),
            Expr::Variable(v, ty) => Expr::Variable(v, ty.reify_in(env)),
        }
    }
}

impl Pattern<Ty> {
    fn collect_vars(&self, vars: &mut LinkedHashSet<SubstVar>) {
        match *self {
            Pattern::Binding(_, ref ty) | Pattern::Literal(_, ref ty) => {
                ty.collect_vars(vars);
            }
            Pattern::Cons(ref h, ref t, ref ty) => {
                h.collect_vars(vars);
                t.collect_vars(vars);
                ty.collect_vars(vars);
            }
        }
    }

    fn reify_in(self, env: &[SubstVar]) -> Pattern<Type> {
        match self {
            Pattern::Binding(n, ty) => Pattern::Binding(n, ty.reify_in(env)),
            Pattern::Cons(h, t, ty) => Pattern::Cons(
                Box::new(h.reify_in(env)),
                Box::new(t.reify_in(env)),
                ty.reify_in(env),
            ),
            Pattern::Literal(l, ty) => Pattern::Literal(l, ty.reify_in(env)),
        }
    }
}

impl Ty {
    fn collect_vars(&self, vars: &mut LinkedHashSet<SubstVar>) {
        match *self {
            Ty::Func(ref l, ref r) => {
                l.collect_vars(vars);
                r.collect_vars(vars);
            }
            Ty::Bool | Ty::Int => {}
            Ty::List(ref t) => t.collect_vars(vars),
            Ty::Var(v) => {
                vars.insert(v);
            }
        }
    }

    fn reify_in(self, env: &[SubstVar]) -> Type {
        match self {
            Ty::Bool => Type::Bool,
            Ty::Func(l, r) => Type::Func(Box::new(l.reify_in(env)), Box::new(r.reify_in(env))),
            Ty::Int => Type::Int,
            Ty::List(t) => Type::List(Box::new(t.reify_in(env))),
            Ty::Var(v) => {
                for (i, &v2) in env.iter().enumerate() {
                    if v == v2 {
                        return Type::Var(i);
                    }
                }
                panic!("Error: unknown var {:?} in env {:?}", v, env)
            }
        }
    }
}

impl Type {
    pub(in typeck) fn unreify(&self) -> Ty {
        fn helper(mut ty: &Type, mut env: UnreifyEnv) -> Ty {
            // First, peel off any Foralls.
            while let Type::Forall(ref t) = *ty {
                env.push(SubstVar::fresh());
                ty = t;
            }

            match *ty {
                Type::Bool => Ty::Bool,
                Type::Forall(_) => unreachable!(),
                Type::Func(ref l, ref r) => {
                    let l = helper(l, env.clone());
                    let r = helper(r, env);
                    Ty::Func(Box::new(l), Box::new(r))
                }
                Type::Int => Ty::Int,
                Type::List(ref t) => Ty::List(Box::new(helper(t, env))),
                Type::Var(n) => Ty::Var(env.get(n)),
            }
        }
        helper(self, UnreifyEnv::new())
    }
}