[Init&Scanning] - Chapter 4 follow up

- Chapter 4 follow up from the "crafting interpreters" book
- Changing the package name ``com.craftinginterpreters.lox`` to ``com.lox``

.gitignore

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+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+out/
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
+replay_pid*

README.md

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+# jlox: the lox java implementation follow up from CraftingInterpreters
+The java implementation for the lox language from the reading of Crafting Interpreters

run.sh

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+#!/bin/bash
+
+# Compile
+javac -d out src/com/lox/*.java
+
+# Run 
+
+java -cp out com.lox.Lox
+

shell.nix

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+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  buildInputs = [
+    pkgs.openjdk
+  ];
+
+  shellHook = ''
+    chmod +x run.sh
+    echo "Java environment is ready. You can now compile and run your Java programs."    
+  '';
+}
+

src/com/lox/Lox.java

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+package com.lox;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+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 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;
+  }
+
+
+  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 {
+    InputStreamReader input = new InputStreamReader(System.in);
+    BufferedReader reader = new BufferedReader(input);
+
+    for (;;) { 
+      System.out.print("> ");
+      String line = reader.readLine();
+      if (line == null) break;
+      run(line);
+      hadError = false;
+    }
+  }
+}

src/com/lox/Scanner.java

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+package com.lox;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static com.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 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;
+      case 'o':
+	if (match('r')) {
+	   addToken(OR);
+  	}
+  	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;
+    }
+
+    // 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() {
+    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));
+  } 
+}

src/com/lox/Token.java

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+package com.lox;
+
+class Token {
+  final TokenType type;
+  final String lexeme;
+  final Object literal;
+  final int line; 
+
+  Token(TokenType type, String lexeme, Object literal, int line) {
+    this.type = type;
+    this.lexeme = lexeme;
+    this.literal = literal;
+    this.line = line;
+  }
+
+  public String toString() {
+    return type + " " + lexeme + " " + literal;
+  }
+}

src/com/lox/TokenType.java

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+package com.lox;
+
+enum TokenType {
+  // Single-character tokens.
+  LEFT_PAREN, RIGHT_PAREN, LEFT_BRACE, RIGHT_BRACE,
+  COMMA, DOT, MINUS, PLUS, SEMICOLON, SLASH, STAR,
+
+  // One or two character tokens.
+  BANG, BANG_EQUAL,
+  EQUAL, EQUAL_EQUAL,
+  GREATER, GREATER_EQUAL,
+  LESS, LESS_EQUAL,
+
+  // Literals.
+  IDENTIFIER, STRING, NUMBER,
+
+  // Keywords.
+  AND, CLASS, ELSE, FALSE, FUN, FOR, IF, NIL, OR,
+  PRINT, RETURN, SUPER, THIS, TRUE, VAR, WHILE,
+
+  EOF
+}
+