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
|
#[derive(Debug, PartialEq)]
pub enum Token {
Eof,
Def,
Extern,
Identifier(String),
Number(f64),
Char(char),
If,
Then,
Else,
}
pub struct Lexer<I>
where
I: Iterator<Item = char>,
{
input: I,
last_char: Option<char>,
}
impl<I> Lexer<I>
where
I: Iterator<Item = char>,
{
pub fn new(mut input: I) -> Lexer<I> {
let last_char = input.next();
Lexer { input, last_char }
}
fn step(&mut self) -> Option<char> {
self.last_char = self.input.next();
self.last_char
}
/// Lex and return the next token.
///
/// Implement `int gettok();` from the tutorial.
pub fn gettok(&mut self) -> Token {
// Eat up whitespaces.
while matches!(self.last_char, Some(c) if c.is_ascii_whitespace()) {
self.step();
}
// Unpack last char or return EOF.
let last_char = if let Some(c) = self.last_char {
c
} else {
return Token::Eof;
};
// Identifier: [a-zA-Z][a-zA-Z0-9]*
if last_char.is_ascii_alphabetic() {
let mut ident = String::new();
ident.push(last_char);
while let Some(c) = self.step() {
if c.is_ascii_alphanumeric() {
ident.push(c)
} else {
break;
}
}
match ident.as_ref() {
"def" => return Token::Def,
"extern" => return Token::Extern,
"if" => return Token::If,
"then" => return Token::Then,
"else" => return Token::Else,
_ => {}
}
return Token::Identifier(ident);
}
// Number: [0-9.]+
if last_char.is_ascii_digit() || last_char == '.' {
let mut num = String::new();
num.push(last_char);
while let Some(c) = self.step() {
if c.is_ascii_digit() || c == '.' {
num.push(c)
} else {
break;
}
}
let num: f64 = num.parse().unwrap_or_default();
return Token::Number(num);
}
// Eat up comment.
if last_char == '#' {
loop {
match self.step() {
Some(c) if c == '\r' || c == '\n' => return self.gettok(),
None => return Token::Eof,
_ => { /* consume comment */ }
}
}
}
// Advance last char and return currently last char.
self.step();
Token::Char(last_char)
}
}
#[cfg(test)]
mod test {
use super::{Lexer, Token};
#[test]
fn test_identifier() {
let mut lex = Lexer::new("a b c".chars());
assert_eq!(Token::Identifier("a".into()), lex.gettok());
assert_eq!(Token::Identifier("b".into()), lex.gettok());
assert_eq!(Token::Identifier("c".into()), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
}
#[test]
fn test_keyword() {
let mut lex = Lexer::new("def extern".chars());
assert_eq!(Token::Def, lex.gettok());
assert_eq!(Token::Extern, lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
}
#[test]
fn test_number() {
let mut lex = Lexer::new("12.34".chars());
assert_eq!(Token::Number(12.34f64), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
let mut lex = Lexer::new(" 1.0 2.0 3.0".chars());
assert_eq!(Token::Number(1.0f64), lex.gettok());
assert_eq!(Token::Number(2.0f64), lex.gettok());
assert_eq!(Token::Number(3.0f64), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
let mut lex = Lexer::new("12.34.56".chars());
assert_eq!(Token::Number(0f64), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
}
#[test]
fn test_comment() {
let mut lex = Lexer::new("# some comment".chars());
assert_eq!(Token::Eof, lex.gettok());
let mut lex = Lexer::new("abc # some comment \n xyz".chars());
assert_eq!(Token::Identifier("abc".into()), lex.gettok());
assert_eq!(Token::Identifier("xyz".into()), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
}
#[test]
fn test_chars() {
let mut lex = Lexer::new("a+b-c".chars());
assert_eq!(Token::Identifier("a".into()), lex.gettok());
assert_eq!(Token::Char('+'), lex.gettok());
assert_eq!(Token::Identifier("b".into()), lex.gettok());
assert_eq!(Token::Char('-'), lex.gettok());
assert_eq!(Token::Identifier("c".into()), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
}
#[test]
fn test_whitespaces() {
let mut lex = Lexer::new(" +a b c! ".chars());
assert_eq!(Token::Char('+'), lex.gettok());
assert_eq!(Token::Identifier("a".into()), lex.gettok());
assert_eq!(Token::Identifier("b".into()), lex.gettok());
assert_eq!(Token::Identifier("c".into()), lex.gettok());
assert_eq!(Token::Char('!'), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
let mut lex = Lexer::new("\n a \n\r b \r \n c \r\r \n ".chars());
assert_eq!(Token::Identifier("a".into()), lex.gettok());
assert_eq!(Token::Identifier("b".into()), lex.gettok());
assert_eq!(Token::Identifier("c".into()), lex.gettok());
assert_eq!(Token::Eof, lex.gettok());
}
#[test]
fn test_ite() {
let mut lex = Lexer::new("if then else".chars());
assert_eq!(Token::If, lex.gettok());
assert_eq!(Token::Then, lex.gettok());
assert_eq!(Token::Else, lex.gettok());
}
}
|
