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
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
|
mod error;
mod value;
pub use self::error::{Error, Result};
pub use self::value::{Function, Value};
use crate::ast::hir::{Binding, Expr};
use crate::ast::{BinaryOperator, FunctionType, Ident, Literal, Type, UnaryOperator};
use crate::common::env::Env;
#[derive(Debug, Default)]
pub struct Interpreter<'a> {
env: Env<&'a Ident<'a>, Value<'a>>,
}
impl<'a> Interpreter<'a> {
pub fn new() -> Self {
Self::default()
}
fn resolve(&self, var: &'a Ident<'a>) -> Result<Value<'a>> {
self.env
.resolve(var)
.cloned()
.ok_or_else(|| Error::UndefinedVariable(var.to_owned()))
}
pub fn eval(&mut self, expr: &'a Expr<'a, Type>) -> Result<Value<'a>> {
let res = match expr {
Expr::Ident(id, _) => self.resolve(id),
Expr::Literal(Literal::Int(i), _) => Ok((*i).into()),
Expr::Literal(Literal::Bool(b), _) => Ok((*b).into()),
Expr::Literal(Literal::String(s), _) => Ok(s.clone().into()),
Expr::UnaryOp { op, rhs, .. } => {
let rhs = self.eval(rhs)?;
match op {
UnaryOperator::Neg => -rhs,
_ => unimplemented!(),
}
}
Expr::BinaryOp { lhs, op, rhs, .. } => {
let lhs = self.eval(lhs)?;
let rhs = self.eval(rhs)?;
match op {
BinaryOperator::Add => lhs + rhs,
BinaryOperator::Sub => lhs - rhs,
BinaryOperator::Mul => lhs * rhs,
BinaryOperator::Div => lhs / rhs,
BinaryOperator::Pow => todo!(),
BinaryOperator::Equ => Ok(lhs.eq(&rhs).into()),
BinaryOperator::Neq => todo!(),
}
}
Expr::Let { bindings, body, .. } => {
self.env.push();
for Binding { ident, body, .. } in bindings {
let val = self.eval(body)?;
self.env.set(ident, val);
}
let res = self.eval(body)?;
self.env.pop();
Ok(res)
}
Expr::If {
condition,
then,
else_,
..
} => {
let condition = self.eval(condition)?;
if *(condition.as_type::<bool>()?) {
self.eval(then)
} else {
self.eval(else_)
}
}
Expr::Call { ref fun, args, .. } => {
let fun = self.eval(fun)?;
let expected_type = FunctionType {
args: args.iter().map(|_| Type::Int).collect(),
ret: Box::new(Type::Int),
};
let Function {
args: function_args,
body,
..
} = fun.as_function(expected_type)?;
let arg_values = function_args.iter().zip(
args.iter()
.map(|v| self.eval(v))
.collect::<Result<Vec<_>>>()?,
);
let mut interpreter = Interpreter::new();
for (arg_name, arg_value) in arg_values {
interpreter.env.set(arg_name, arg_value);
}
Ok(Value::from(*interpreter.eval(body)?.as_type::<i64>()?))
}
Expr::Fun { args, body, type_ } => {
let type_ = match type_ {
Type::Function(ft) => ft.clone(),
_ => unreachable!("Function expression without function type"),
};
Ok(Value::from(value::Function {
// TODO
type_,
args: args.iter().map(|(arg, _)| arg.to_owned()).collect(),
body: (**body).to_owned(),
}))
}
}?;
debug_assert_eq!(&res.type_(), expr.type_());
Ok(res)
}
}
pub fn eval<'a>(expr: &'a Expr<'a, Type>) -> Result<Value<'a>> {
let mut interpreter = Interpreter::new();
interpreter.eval(expr)
}
#[cfg(test)]
mod tests {
use std::convert::TryFrom;
use super::value::{TypeOf, Val};
use super::*;
use BinaryOperator::*;
fn int_lit(i: u64) -> Box<Expr<'static, Type<'static>>> {
Box::new(Expr::Literal(Literal::Int(i), Type::Int))
}
fn do_eval<T>(src: &str) -> T
where
for<'a> &'a T: TryFrom<&'a Val<'a>>,
T: Clone + TypeOf,
{
let expr = crate::parser::expr(src).unwrap().1;
let hir = crate::tc::typecheck_expr(expr).unwrap();
let res = eval(&hir).unwrap();
res.as_type::<T>().unwrap().clone()
}
#[test]
fn simple_addition() {
let expr = Expr::BinaryOp {
lhs: int_lit(1),
op: Mul,
rhs: int_lit(2),
type_: Type::Int,
};
let res = eval(&expr).unwrap();
assert_eq!(*res.as_type::<i64>().unwrap(), 2);
}
#[test]
fn variable_shadowing() {
let res = do_eval::<i64>("let x = 1 in (let x = 2 in x) + x");
assert_eq!(res, 3);
}
#[test]
fn conditional_with_equals() {
let res = do_eval::<i64>("let x = 1 in if x == 1 then 2 else 4");
assert_eq!(res, 2);
}
#[test]
#[ignore]
fn function_call() {
let res = do_eval::<i64>("let id = fn x = x in id 1");
assert_eq!(res, 1);
}
}
|
