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
|
package com.craftinginterpreters.lox;
import static com.craftinginterpreters.lox.TokenType.*;
import java.util.ArrayList;
import java.util.List;
class Parser {
private static class ParseError extends RuntimeException {
}
private final List<Token> tokens;
private int current = 0;
Parser(List<Token> tokens) {
this.tokens = tokens;
}
public List<Stmt> parse() {
List<Stmt> statements = new ArrayList<>();
while (!isAtEnd()) {
statements.add(statement());
}
return statements;
}
private Expr expression() {
return equality();
}
private Stmt statement() {
if (match(PRINT))
return printStatement();
return expressionStatement();
}
private Stmt printStatement() {
Expr value = expression();
consume(SEMICOLON, "Expect ';' after value.");
return new Stmt.Print(value);
}
private Stmt expressionStatement() {
Expr expr = expression();
consume(SEMICOLON, "Expect ';' after expression.");
return new Stmt.Expression(expr);
}
private Expr equality() {
Expr expr = comparison();
while (match(BANG_EQUAL, EQUAL_EQUAL)) {
Token operator = previous();
Expr right = comparison();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr comparison() {
Expr expr = term();
while (match(GREATER, GREATER_EQUAL, LESS, LESS_EQUAL)) {
Token operator = previous();
Expr right = term();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr term() {
Expr expr = factor();
while (match(MINUS, PLUS)) {
Token operator = previous();
Expr right = factor();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr factor() {
Expr expr = unary();
while (match(SLASH, STAR)) {
Token operator = previous();
Expr right = unary();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr unary() {
if (match(BANG, MINUS)) {
Token operator = previous();
Expr right = unary();
return new Expr.Unary(operator, right);
}
return primary();
}
private Expr primary() {
if (match(FALSE))
return new Expr.Literal(false);
if (match(TRUE))
return new Expr.Literal(true);
if (match(NIL))
return new Expr.Literal(null);
if (match(NUMBER, STRING)) {
return new Expr.Literal(previous().literal);
}
if (match(LEFT_PAREN)) {
Expr expr = expression();
consume(RIGHT_PAREN, "Expect ')' after expression.");
return new Expr.Grouping(expr);
}
throw error(peek(), "Expect expression.");
}
private boolean match(TokenType... types) {
for (TokenType type : types) {
if (check(type)) {
advance();
return true;
}
}
return false;
}
private Token consume(TokenType type, String message) {
if (check(type))
return advance();
throw error(peek(), message);
}
private boolean check(TokenType type) {
if (isAtEnd())
return false;
return peek().type == type;
}
private Token advance() {
if (!isAtEnd())
current++;
return previous();
}
private boolean isAtEnd() {
return peek().type == EOF;
}
private Token peek() {
return tokens.get(current);
}
private Token previous() {
return tokens.get(current - 1);
}
private ParseError error(Token token, String message) {
Lox.error(token, message);
return new ParseError();
}
private void synchronize() {
advance();
while (!isAtEnd()) {
if (previous().type == SEMICOLON)
return;
switch (peek().type) {
case CLASS:
case FUN:
case VAR:
case FOR:
case IF:
case WHILE:
case PRINT:
case RETURN:
return;
}
advance();
}
}
}
|
