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Chapter 4: Scanning

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This commit is contained in:
Michael Thomson 2025-04-09 20:17:32 -04:00
parent 94aca70c09
commit 3a6e4e7833
2 changed files with 181 additions and 13 deletions
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4
jlox/src/main/java/com/craftinginterpreters/lox/Lox.java
View File

@ -36,7 +36,7 @@ public class Lox {
BufferedReader reader = new BufferedReader(input);
for (;;) {
System.out.println("> ");
System.out.print("> ");
String line = reader.readLine();
if (line == null) break;
run(line);
@ -58,7 +58,7 @@ public class Lox {
}
private static void report(int line, String where, String message) {
System.err.println("[line " + line + "] Error" + where + ": " + message););
System.err.println("[line " + line + "] Error" + where + ": " + message);
hadError = true;
}
}

190
jlox/src/main/java/com/craftinginterpreters/lox/Scanner.java
View File

@ -1,7 +1,9 @@
package com.craftinginterpreters.lox;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
class Scanner {
private final String source;
@ -10,6 +12,28 @@ class Scanner {
private int current = 0;
private int line = 1;
private static final Map<String, TokenType> keywords;
static {
keywords = new HashMap<>();
keywords.put("and", TokenType.AND);
keywords.put("class", TokenType.CLASS);
keywords.put("else", TokenType.ELSE);
keywords.put("false", TokenType.FALSE);
keywords.put("for", TokenType.FOR);
keywords.put("fun", TokenType.FUN);
keywords.put("if", TokenType.IF);
keywords.put("nil", TokenType.NIL);
keywords.put("or", TokenType.OR);
keywords.put("print", TokenType.PRINT);
keywords.put("return", TokenType.RETURN);
keywords.put("super", TokenType.SUPER);
keywords.put("this", TokenType.THIS);
keywords.put("true", TokenType.TRUE);
keywords.put("var", TokenType.VAR);
keywords.put("while", TokenType.WHILE);
}
public Scanner(String source) {
this.source = source;
}
@ -27,19 +51,163 @@ class Scanner {
private void scanToken() {
char c = advance();
switch (c) {
case '(': addToken(TokenType.LEFT_PAREN); break;
case ')': addToken(TokenType.RIGHT_PAREN); break;
case '{': addToken(TokenType.LEFT_BRACE); break;
case '}': addToken(TokenType.RIGHT_BRACE); break;
case ',': addToken(TokenType.COMMA); break;
case '.': addToken(TokenType.DOT); break;
case '-': addToken(TokenType.MINUS); break;
case '+': addToken(TokenType.PLUS); break;
case ';': addToken(TokenType.SEMICOLON); break;
case '*': addToken(TokenType.STAR); break;
case '(':
addToken(TokenType.LEFT_PAREN);
break;
case ')':
addToken(TokenType.RIGHT_PAREN);
break;
case '{':
addToken(TokenType.LEFT_BRACE);
break;
case '}':
addToken(TokenType.RIGHT_BRACE);
break;
case ',':
addToken(TokenType.COMMA);
break;
case '.':
addToken(TokenType.DOT);
break;
case '-':
addToken(TokenType.MINUS);
break;
case '+':
addToken(TokenType.PLUS);
break;
case ';':
addToken(TokenType.SEMICOLON);
break;
case '*':
addToken(TokenType.STAR);
break;
case '!':
addToken(match('=') ? TokenType.BANG_EQUAL : TokenType.BANG);
break;
case '=':
addToken(match('=') ? TokenType.EQUAL_EQUAL : TokenType.EQUAL);
break;
case '<':
addToken(match('=') ? TokenType.LESS_EQUAL : TokenType.LESS);
break;
case '>':
addToken(match('=') ? TokenType.GREATER_EQUAL : TokenType.GREATER);
break;
case '/':
if (match('/')) {
while (peek() != '\n' && !isAtEnd())
advance();
} else {
addToken(TokenType.SLASH);
}
break;
case ' ':
case '\r':
case '\t':
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();
String text = source.substring(start, current);
TokenType type = keywords.get(text);
if (type == null) type = TokenType.IDENTIFIER;
addToken(type);
}
private void number() {
while (isDigit(peek()))
advance();
// Look for a fractional part
if (peek() == '.' && isDigit(peekNext())) {
advance();
while (isDigit(peek()))
advance();
}
addToken(TokenType.NUMBER, Double.parseDouble(source.substring(start, current)));
}
private void string() {
while (peek() != '"' && !isAtEnd()) {
if (peek() == '\n')
line++;
advance();
}
if (isAtEnd()) {
Lox.error(line, "Unterminated string.");
return;
}
// the closing "
advance();
// trim quotes
String value = source.substring(start + 1, current - 1);
addToken(TokenType.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();
}
@ -53,7 +221,7 @@ class Scanner {
}
private void addToken(TokenType type, Object literal) {
String text = source.substring(start, current);
String text = source.substring(start, current);
tokens.add(new Token(type, text, literal, line));
}
}