Jlox解释器的源代码和词法扫描
时间: 2024-03-23 18:43:06 浏览: 12
Jlox是一个用Java编写的lox语言解释器,它包含了词法扫描和语法分析等功能。以下是Jlox的源代码和词法扫描器部分的示例代码:
### Lox.java
```java
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
public class Lox {
static boolean hadError = false;
public static void main(String[] args) throws IOException {
if (args.length > 1) {
System.out.println("Usage: jlox [script]");
System.exit(64);
} else if (args.length == 1) {
runFile(args[0]);
} else {
runPrompt();
}
}
private static void runFile(String path) throws IOException {
byte[] bytes = Files.readAllBytes(Paths.get(path));
run(new String(bytes, Charset.defaultCharset()));
if (hadError) System.exit(65);
}
private static void runPrompt() throws IOException {
System.out.println("Welcome to the JLox REPL!");
for (;;) {
System.out.print("> ");
run(new java.util.Scanner(System.in).nextLine());
hadError = false;
}
}
private static void run(String source) {
Scanner scanner = new Scanner(source);
List<Token> tokens = scanner.scanTokens();
// For now, just print the tokens.
for (Token token : tokens) {
System.out.println(token);
}
}
static void error(int line, String message) {
report(line, "", message);
}
private static void report(int line, String where, String message) {
System.err.println(
"[line " + line + "] Error" + where + ": " + message);
hadError = true;
}
}
```
### Scanner.java
```java
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import static TokenType.*;
class Scanner {
private final String source;
private final List<Token> tokens = new ArrayList<>();
private int start = 0;
private int current = 0;
private int line = 1;
private static final Map<String, TokenType> keywords;
static {
keywords = new HashMap<>();
keywords.put("and", AND);
keywords.put("class", CLASS);
keywords.put("else", ELSE);
keywords.put("false", FALSE);
keywords.put("for", FOR);
keywords.put("fun", FUN);
keywords.put("if", IF);
keywords.put("nil", NIL);
keywords.put("or", OR);
keywords.put("print", PRINT);
keywords.put("return", RETURN);
keywords.put("super", SUPER);
keywords.put("this", THIS);
keywords.put("true", TRUE);
keywords.put("var", VAR);
keywords.put("while", WHILE);
}
Scanner(String source) {
this.source = source;
}
List<Token> scanTokens() {
while (!isAtEnd()) {
// We are at the beginning of the next lexeme.
start = current;
scanToken();
}
tokens.add(new Token(EOF, "", null, line));
return tokens;
}
private void scanToken() {
char c = advance();
switch (c) {
case '(': addToken(LEFT_PAREN); break;
case ')': addToken(RIGHT_PAREN); break;
case '{': addToken(LEFT_BRACE); break;
case '}': addToken(RIGHT_BRACE); break;
case ',': addToken(COMMA); break;
case '.': addToken(DOT); break;
case '-': addToken(MINUS); break;
case '+': addToken(PLUS); break;
case ';': addToken(SEMICOLON); break;
case '*': addToken(STAR); break;
case '!': addToken(match('=') ? BANG_EQUAL : BANG); break;
case '=': addToken(match('=') ? EQUAL_EQUAL : EQUAL); break;
case '<': addToken(match('=') ? LESS_EQUAL : LESS); break;
case '>': addToken(match('=') ? GREATER_EQUAL : GREATER); break;
case '/':
if (match('/')) {
// A comment goes until the end of the line.
while (peek() != '\n' && !isAtEnd()) advance();
} else {
addToken(SLASH);
}
break;
case ' ':
case '\r':
case '\t':
// Ignore whitespace.
break;
case '\n':
line++;
break;
case '"': string(); break;
default:
if (isDigit(c)) {
number();
} else if (isAlpha(c)) {
identifier();
} else {
Lox.error(line, "Unexpected character.");
}
break;
}
}
private void identifier() {
while (isAlphaNumeric(peek())) advance();
// See if the identifier is a reserved word.
String text = source.substring(start, current);
TokenType type = keywords.get(text);
if (type == null) type = IDENTIFIER;
addToken(type);
}
private void number() {
while (isDigit(peek())) advance();
// Look for a fractional part.
if (peek() == '.' && isDigit(peekNext())) {
// Consume the "."
advance();
while (isDigit(peek())) advance();
}
addToken(NUMBER,
Double.parseDouble(source.substring(start, current)));
}
private void string() {
while (peek() != '"' && !isAtEnd()) {
if (peek() == '\n') line++;
advance();
}
// Unterminated string.
if (isAtEnd()) {
Lox.error(line, "Unterminated string.");
return;
}
// The closing ".
advance();
// Trim the surrounding quotes.
String value = source.substring(start + 1, current - 1);
addToken(STRING, value);
}
private boolean match(char expected) {
if (isAtEnd()) return false;
if (source.charAt(current) != expected) return false;
current++;
return true;
}
private char peek() {
if (isAtEnd()) return '\0';
return source.charAt(current);
}
private char peekNext() {
if (current + 1 >= source.length()) return '\0';
return source.charAt(current + 1);
}
private boolean isAlpha(char c) {
return (c >= 'a' && c <= 'z') ||
(c >= 'A' && c <= 'Z') ||
c == '_';
}
private boolean isAlphaNumeric(char c) {
return isAlpha(c) || isDigit(c);
}
private boolean isDigit(char c) {
return c >= '0' && c <= '9';
}
private boolean isAtEnd() {
return current >= source.length();
}
private char advance() {
current++;
return source.charAt(current - 1);
}
private void addToken(TokenType type) {
addToken(type, null);
}
private void addToken(TokenType type, Object literal) {
String text = source.substring(start, current);
tokens.add(new Token(type, text, literal, line));
}
}
```
这些代码只是Jlox解释器的一部分,但它们展示了如何实现词法扫描器和一些简单的语法分析。