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
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
|
/// This is the parser and interpreter for the 'Foo' language. See `tutorial.md` in the repository's root to learn
/// about it.
use chumsky::prelude::*;
#[derive(Debug)]
enum Expr {
Num(f64),
Var(String),
Neg(Box<Expr>),
Add(Box<Expr>, Box<Expr>),
Sub(Box<Expr>, Box<Expr>),
Mul(Box<Expr>, Box<Expr>),
Div(Box<Expr>, Box<Expr>),
Call(String, Vec<Expr>),
Let {
name: String,
rhs: Box<Expr>,
then: Box<Expr>,
},
Fn {
name: String,
args: Vec<String>,
body: Box<Expr>,
then: Box<Expr>,
},
}
fn parser() -> impl Parser<char, Expr, Error = Simple<char>> {
let ident = text::ident().padded();
let expr = recursive(|expr| {
let int = text::int(10)
.map(|s: String| Expr::Num(s.parse().unwrap()))
.padded();
let call = ident
.then(
expr.clone()
.separated_by(just(','))
.allow_trailing()
.delimited_by(just('('), just(')')),
)
.map(|(f, args)| Expr::Call(f, args));
let atom = int
.or(expr.delimited_by(just('('), just(')')))
.or(call)
.or(ident.map(Expr::Var));
let op = |c| just(c).padded();
let unary = op('-')
.repeated()
.then(atom)
.foldr(|_op, rhs| Expr::Neg(Box::new(rhs)));
let product = unary
.clone()
.then(
op('*')
.to(Expr::Mul as fn(_, _) -> _)
.or(op('/').to(Expr::Div as fn(_, _) -> _))
.then(unary)
.repeated(),
)
.foldl(|lhs, (op, rhs)| op(Box::new(lhs), Box::new(rhs)));
let sum = product
.clone()
.then(
op('+')
.to(Expr::Add as fn(_, _) -> _)
.or(op('-').to(Expr::Sub as fn(_, _) -> _))
.then(product)
.repeated(),
)
.foldl(|lhs, (op, rhs)| op(Box::new(lhs), Box::new(rhs)));
sum
});
let decl = recursive(|decl| {
let r#let = text::keyword("let")
.ignore_then(ident)
.then_ignore(just('='))
.then(expr.clone())
.then_ignore(just(';'))
.then(decl.clone())
.map(|((name, rhs), then)| Expr::Let {
name,
rhs: Box::new(rhs),
then: Box::new(then),
});
let r#fn = text::keyword("fn")
.ignore_then(ident)
.then(ident.repeated())
.then_ignore(just('='))
.then(expr.clone())
.then_ignore(just(';'))
.then(decl)
.map(|(((name, args), body), then)| Expr::Fn {
name,
args,
body: Box::new(body),
then: Box::new(then),
});
r#let.or(r#fn).or(expr).padded()
});
decl.then_ignore(end())
}
fn eval<'a>(
expr: &'a Expr,
vars: &mut Vec<(&'a String, f64)>,
funcs: &mut Vec<(&'a String, &'a [String], &'a Expr)>,
) -> Result<f64, String> {
match expr {
Expr::Num(x) => Ok(*x),
Expr::Neg(a) => Ok(-eval(a, vars, funcs)?),
Expr::Add(a, b) => Ok(eval(a, vars, funcs)? + eval(b, vars, funcs)?),
Expr::Sub(a, b) => Ok(eval(a, vars, funcs)? - eval(b, vars, funcs)?),
Expr::Mul(a, b) => Ok(eval(a, vars, funcs)? * eval(b, vars, funcs)?),
Expr::Div(a, b) => Ok(eval(a, vars, funcs)? / eval(b, vars, funcs)?),
Expr::Var(name) => {
if let Some((_, val)) = vars.iter().rev().find(|(var, _)| *var == name) {
Ok(*val)
} else {
Err(format!("Cannot find variable `{}` in scope", name))
}
}
Expr::Let { name, rhs, then } => {
let rhs = eval(rhs, vars, funcs)?;
vars.push((name, rhs));
let output = eval(then, vars, funcs);
vars.pop();
output
}
Expr::Call(name, args) => {
if let Some((_, arg_names, body)) =
funcs.iter().rev().find(|(var, _, _)| *var == name).copied()
{
if arg_names.len() == args.len() {
let mut args = args
.iter()
.map(|arg| eval(arg, vars, funcs))
.zip(arg_names.iter())
.map(|(val, name)| Ok((name, val?)))
.collect::<Result<_, String>>()?;
vars.append(&mut args);
let output = eval(body, vars, funcs);
vars.truncate(vars.len() - args.len());
output
} else {
Err(format!(
"Wrong number of arguments for function `{}`: expected {}, found {}",
name,
arg_names.len(),
args.len(),
))
}
} else {
Err(format!("Cannot find function `{}` in scope", name))
}
}
Expr::Fn {
name,
args,
body,
then,
} => {
funcs.push((name, args, body));
let output = eval(then, vars, funcs);
funcs.pop();
output
}
}
}
fn main() {
let src = std::fs::read_to_string(std::env::args().nth(1).unwrap()).unwrap();
match parser().parse(src) {
Ok(ast) => match eval(&ast, &mut Vec::new(), &mut Vec::new()) {
Ok(output) => println!("{}", output),
Err(eval_err) => println!("Evaluation error: {}", eval_err),
},
Err(parse_errs) => parse_errs
.into_iter()
.for_each(|e| println!("Parse error: {}", e)),
}
}
|
