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
197
198
199
200
201
202
203
204
205
206
207
208
209
210
|
use std::io::{ stdin, stdout };
#[derive(Debug, Copy, Clone, PartialEq)]
pub struct Operator {
token: char,
operation: fn(f64, f64) -> f64,
precedence: u8,
is_left_associative: bool,
}
#[derive(Debug, Copy, Clone)]
pub enum Token {
Operator(Operator),
Num(f64),
LParen,
RParen
}
impl Operator {
fn token_from_op(token: char, operation: fn(f64, f64) -> f64, precedence: u8, is_left_associative: bool) -> Token {
Token::Operator(
Operator {
token,
operation,
precedence,
is_left_associative
}
)
}
fn operate(self, x: f64, y: f64) -> f64 {
(self.operation)(x, y)
}
}
fn main() {
loop {
let mut input = String::new();
stdin().read_line(&mut input).unwrap();
let input = input.trim();
let input = input.replace(" ", "");
if input == "exit" {
return
}
let lexed = lexer(&input[..]);
let postfixed = to_postfix(lexed.unwrap());
let evaled = eval_postfix(postfixed.unwrap());
println!("{}", evaled.unwrap());
}
}
fn lexer(input: &str) -> Result<Vec<Token>, String> {
let mut num_vec: String = String::new();
let mut result: Vec<Token> = vec![];
for letter in input.chars() {
match letter {
'0'...'9' | '.' => {
num_vec.push(letter);
},
'+' | '-' | '/' | '*' | '^' => {
// parse num buf
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
num_vec.clear();
}
// finish
let operator_token: Token = match letter {
'+' => Operator::token_from_op('+', |x, y| x + y, 2, true),
'-' => Operator::token_from_op('-', |x, y| x - y, 2, true),
'/' => Operator::token_from_op('/', |x, y| x / y, 3, true),
'*' => Operator::token_from_op('*', |x, y| x * y, 3, true),
'^' => Operator::token_from_op('^', |x, y| x.powf(y), 4, false),
_ => panic!("unexpected op whuuu"),
};
result.push(operator_token);
},
'(' => {
// parse num buf
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
result.push(Operator::token_from_op('*', |x, y| x * y, 3, true));
num_vec.clear();
}
if let Some(x) = result.last() {
match x {
Token::RParen => {
result.push(Operator::token_from_op('*', |x, y| x * y, 3, true));
},
_ => {}
};
}
// finish
result.push(Token::LParen);
},
')' => {
// parse num buf
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
num_vec.clear();
}
// finish
result.push(Token::RParen);
}
' ' => {}
_ => {
return Err(format!("Unexpected character: {}", letter))
}
}
}
let parse_num = num_vec.parse::<f64>().ok();
if let Some(x) = parse_num {
result.push(Token::Num(x));
num_vec.clear();
}
Ok(result)
}
fn to_postfix(tokens: Vec<Token>) -> Result<Vec<Token>, String> {
let mut postfixed: Vec<Token> = vec![];
let mut op_stack: Vec<Token> = vec![];
for token in tokens {
match token {
Token::Num(_) => {
postfixed.push(token);
},
Token::Operator(current_op) => {
while let Some(top_op) = op_stack.last() {
match top_op {
Token::LParen => {
break;
}
Token::Operator(top_op) => {
let tp = top_op.precedence;
let cp = current_op.precedence;
if tp > cp || (tp == cp && top_op.is_left_associative) {
postfixed.push(op_stack.pop().unwrap());
} else {
break;
}
}
_ => {
return Err(format!("Unexpected match branch part 2"))
}
}
}
op_stack.push(token);
},
Token::LParen => {
op_stack.push(token);
},
Token::RParen => {
let mut found: bool = false;
while let Some(top_op) = op_stack.last() {
match top_op {
Token::LParen => {
let _ = op_stack.pop().unwrap();
found = true;
},
_ => {
postfixed.push(op_stack.pop().unwrap());
}
}
}
if found == false {
return Err(format!("Mismatched parentheses part 2"))
}
}
}
}
while let Some(op) = op_stack.pop() {
postfixed.push(op);
}
Ok(postfixed)
}
fn eval_postfix(postfixed: Vec<Token>) -> Result<f64, String> {
let mut num_stack: Vec<f64> = vec![];
for token in postfixed {
match token {
Token::Num(n) => {
num_stack.push(n);
},
Token::Operator(op) => {
if let Some(n2) = num_stack.pop() {
if let Some(n1) = num_stack.pop() {
num_stack.push(op.operate(n1, n2))
} else {
return Err(format!("Too many operators, Too little operands"))
}
} else {
return Err(format!("Too many operators, Too little operands"))
}
}
_ => {
return Err(format!("Yo nibba how did this get here"))
}
}
}
if num_stack.len() == 1 {
Ok(num_stack.pop().unwrap())
} else {
Err(format!("Parser Error"))
}
}
|
