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
|
// This implements the grammar of Lox as described starting in the
// Crafting Interpreters chapter "Representing Code". Note that the
// upstream Java implementation works about Java being bad at value
// classes by writing a code generator for Java.
//
// My Rust implementation skips this step because it's unnecessary, we
// have real types.
use crate::scanner::{Token, TokenKind};
// AST
#[derive(Debug)]
struct Binary<'a> {
left: Box<Expr<'a>>,
right: Box<Expr<'a>>,
operator: Token<'a>,
}
#[derive(Debug)]
struct Grouping<'a>(Box<Expr<'a>>);
#[derive(Debug)]
struct Literal(TokenKind);
#[derive(Debug)]
enum Expr<'a> {
Binary(Binary<'a>),
Grouping(Grouping<'a>),
Literal(Literal),
}
// Parser
/*
expression → equality ;
equality → comparison ( ( "!=" | "==" ) comparison )* ;
comparison → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
term → factor ( ( "-" | "+" ) factor )* ;
factor → unary ( ( "/" | "*" ) unary )* ;
unary → ( "!" | "-" ) unary
| primary ;
primary → NUMBER | STRING | "true" | "false" | "nil"
| "(" expression ")" ;
*/
struct Parser<'a> {
tokens: Vec<Token<'a>>,
current: usize,
}
impl<'a> Parser<'a> {
// recursive-descent parser functions
fn expression(&mut self) -> Expr<'a> {
self.equality()
}
fn equality(&mut self) -> Expr<'a> {
let expr = self.comparison();
unimplemented!()
}
fn comparison(&mut self) -> Expr<'a> {
unimplemented!()
}
// internal helpers
fn match_token(&mut self, oneof: &[TokenKind]) -> bool {
for token in oneof {
if self.check_token(token) {
self.advance();
return true;
}
}
return false;
}
fn advance(&mut self) -> &Token {
if !self.is_at_end() {
self.current += 1;
}
return self.previous();
}
fn is_at_end(&self) -> bool {
self.check_token(&TokenKind::Eof)
}
fn check_token(&self, token: &TokenKind) -> bool {
self.peek().kind == *token
}
fn peek(&self) -> &Token {
&self.tokens[self.current]
}
fn previous(&self) -> &Token {
&self.tokens[self.current - 1]
}
}
|
