Initial commit

java/com/craftinginterpreters/lox/Scanner.java

@@ -0,0 +1,229 @@
+package com.craftinginterpreters.lox;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static com.craftinginterpreters.lox.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 boolean isAtEnd() {
+    return current >= source.length();
+  }
+
+  private char advance() {
+    return source.charAt(current++);
+  }
+
+  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));
+  }
+
+  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();
+
+    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();
+    }
+
+    if (isAtEnd()) {
+      Lox.error(line, "Unterminated string.");
+      return;
+    }
+
+    advance(); // The closing ".
+
+    // 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';
+  }
+}