commit 84e04fbe159435a02fa3fac6525795ef4b2afc19
Author: Michael Smith <m@michaelsmith.be>
Date:   Wed Jun 29 16:38:57 2022 +0200

    Initial commit

diff --git a/java/com/craftinginterpreters/lox/AstPrinter.java b/java/com/craftinginterpreters/lox/AstPrinter.java
new file mode 100644
index 0000000..23f4655
--- /dev/null
+++ b/java/com/craftinginterpreters/lox/AstPrinter.java
@@ -0,0 +1,50 @@
+package com.craftinginterpreters.lox;
+
+class AstPrinter implements Expr.Visitor<String> {
+  String print(Expr expr) {
+    return expr.accept(this);
+  }
+
+  @Override
+  public String visitBinaryExpr(Expr.Binary expr) {
+    return parenthesize(expr.operator.lexeme, expr.left, expr.right);
+  }
+
+  @Override
+  public String visitGroupingExpr(Expr.Grouping expr) {
+    return parenthesize("group", expr.expression);
+  }
+
+  @Override
+  public String visitLiteralExpr(Expr.Literal expr) {
+    if (expr.value == null)
+      return "nil";
+    return expr.value.toString();
+  }
+
+  @Override
+  public String visitUnaryExpr(Expr.Unary expr) {
+    return parenthesize(expr.operator.lexeme, expr.right);
+  }
+
+  private String parenthesize(String name, Expr... exprs) {
+    StringBuilder builder = new StringBuilder();
+
+    builder.append("(").append(name);
+    for (Expr expr : exprs) {
+      builder.append(" ");
+      builder.append(expr.accept(this));
+    }
+    builder.append(")");
+
+    return builder.toString();
+  }
+
+  public static void main(String[] args) {
+    Expr expression = new Expr.Binary(
+        new Expr.Unary(new Token(TokenType.MINUS, "-", null, 1), new Expr.Literal(123)),
+        new Token(TokenType.STAR, "*", null, 1), new Expr.Grouping(new Expr.Literal(45.67)));
+
+    System.out.println(new AstPrinter().print(expression));
+  }
+}
diff --git a/java/com/craftinginterpreters/lox/Expr.java b/java/com/craftinginterpreters/lox/Expr.java
new file mode 100644
index 0000000..0e2c05e
--- /dev/null
+++ b/java/com/craftinginterpreters/lox/Expr.java
@@ -0,0 +1,72 @@
+package com.craftinginterpreters.lox;
+
+import java.util.List;
+
+abstract class Expr {
+  interface Visitor<R> {
+    R visitBinaryExpr(Binary expr);
+    R visitGroupingExpr(Grouping expr);
+    R visitLiteralExpr(Literal expr);
+    R visitUnaryExpr(Unary expr);
+  }
+
+  static class Binary extends Expr {
+    Binary(Expr left, Token operator, Expr right) {
+      this.left = left;
+      this.operator = operator;
+      this.right = right;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitBinaryExpr(this);
+    }
+
+    final Expr left;
+    final Token operator;
+    final Expr right;
+  }
+
+  static class Grouping extends Expr {
+    Grouping(Expr expression) {
+      this.expression = expression;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitGroupingExpr(this);
+    }
+
+    final Expr expression;
+  }
+
+  static class Literal extends Expr {
+    Literal(Object value) {
+      this.value = value;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitLiteralExpr(this);
+    }
+
+    final Object value;
+  }
+
+  static class Unary extends Expr {
+    Unary(Token operator, Expr right) {
+      this.operator = operator;
+      this.right = right;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitUnaryExpr(this);
+    }
+
+    final Token operator;
+    final Expr right;
+  }
+
+  abstract <R> R accept(Visitor<R> visitor);
+}
diff --git a/java/com/craftinginterpreters/lox/Lox.java b/java/com/craftinginterpreters/lox/Lox.java
new file mode 100644
index 0000000..5a33c95
--- /dev/null
+++ b/java/com/craftinginterpreters/lox/Lox.java
@@ -0,0 +1,66 @@
+package com.craftinginterpreters.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 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;
+    }
+  }
+
+  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;
+  }
+
+}
diff --git a/java/com/craftinginterpreters/lox/Scanner.java b/java/com/craftinginterpreters/lox/Scanner.java
new file mode 100644
index 0000000..52c7c27
--- /dev/null
+++ b/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';
+  }
+}
diff --git a/java/com/craftinginterpreters/lox/Token.java b/java/com/craftinginterpreters/lox/Token.java
new file mode 100644
index 0000000..518bc87
--- /dev/null
+++ b/java/com/craftinginterpreters/lox/Token.java
@@ -0,0 +1,19 @@
+package com.craftinginterpreters.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;
+  }
+}
diff --git a/java/com/craftinginterpreters/lox/TokenType.java b/java/com/craftinginterpreters/lox/TokenType.java
new file mode 100644
index 0000000..cbb96ab
--- /dev/null
+++ b/java/com/craftinginterpreters/lox/TokenType.java
@@ -0,0 +1,20 @@
+package com.craftinginterpreters.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
+}
diff --git a/java/com/craftinginterpreters/tool/GenerateAst.java b/java/com/craftinginterpreters/tool/GenerateAst.java
new file mode 100644
index 0000000..ce9a78b
--- /dev/null
+++ b/java/com/craftinginterpreters/tool/GenerateAst.java
@@ -0,0 +1,93 @@
+package com.craftinginterpreters.tool;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.Arrays;
+import java.util.List;
+
+public class GenerateAst {
+  public static void main(String[] args) throws IOException {
+    // if (args.length != 1) {
+    // System.err.println("Usage: generate_ast <output directory>");
+    // System.exit(64);
+    // }
+    // String outputDir = args[0];
+    String outputDir = "com/craftinginterpreters/lox";
+    defineAst(outputDir, "Expr", Arrays.asList(
+        "Binary   : Expr left, Token operator, Expr right",
+        "Grouping : Expr expression",
+        "Literal  : Object value",
+        "Unary    : Token operator, Expr right"));
+  }
+
+  private static void defineAst(
+      String outputDir, String baseName, List<String> types) throws IOException {
+    String path = outputDir + "/" + baseName + ".java";
+    PrintWriter writer = new PrintWriter(path, "UTF-8");
+
+    writer.println("package com.craftinginterpreters.lox;");
+    writer.println();
+    writer.println("import java.util.List;");
+    writer.println();
+    writer.println("abstract class " + baseName + " {");
+
+    defineVisitor(writer, baseName, types);
+
+    // The AST clasess.
+    for (String type : types) {
+      String className = type.split(":")[0].trim();
+      String fields = type.split(":")[1].trim();
+      defineType(writer, baseName, className, fields);
+    }
+
+    // The base accept() method.
+    writer.println("  abstract <R> R accept(Visitor<R> visitor);");
+
+    writer.println("}");
+    writer.close();
+  }
+
+  private static void defineVisitor(PrintWriter writer, String baseName, List<String> types) {
+    writer.println("  interface Visitor<R> {");
+
+    for (String type : types) {
+      String typeName = type.split(":")[0].trim();
+      writer.println("    R visit" + typeName + baseName + "(" + typeName + " " + baseName.toLowerCase() + ");");
+    }
+
+    writer.println("  }");
+    writer.println();
+  }
+
+  private static void defineType(PrintWriter writer, String baseName, String className, String fieldList) {
+    writer.println("  static class " + className + " extends " + baseName + " {");
+
+    // Constructor.
+    writer.println("    " + className + "(" + fieldList + ") {");
+
+    // Store parameters in fields.
+    String[] fields = fieldList.split(", ");
+    for (String field : fields) {
+      String name = field.split(" ")[1];
+      writer.println("      this." + name + " = " + name + ";");
+    }
+
+    writer.println("    }");
+
+    // Visitor pattern.
+    writer.println();
+    writer.println("    @Override");
+    writer.println("    <R> R accept(Visitor<R> visitor) {");
+    writer.println("      return visitor.visit" + className + baseName + "(this);");
+    writer.println("    }");
+
+    // Fields.
+    writer.println();
+    for (String field : fields) {
+      writer.println("    final " + field + ";");
+    }
+
+    writer.println("  }");
+    writer.println();
+  }
+}