Add support for variable environments and declaration; Add nullable and non-nullable types

.gitignore

@@ -0,0 +1,2 @@
+*.class
+

README.md

@@ -1,2 +1,6 @@
-# CobaltScript
-A small programming language designed for general purpose scripting and for learning interpreter design
+# Cobalt
+Cobalt is a small programming language designed for general purpose and systems level scripting. This project follows very closely to the curriculum from [Crafting Interpreters](http://craftinginterpreters.com/) by Robert Nystrom, and is intended to be a pet project for myself to learn programming language design and interpreter design concepts.
+
+Currently, Cobalt follows the same grammer and design structure as [Lox](https://github.com/munificent/craftinginterpreters), the language featured in Nystrom's book. However, I eventually plan to mutate Cobalt from these design patterns and create a unique syntax and structure once I have reached a high enough proficiency.
+
+This project is a **work in progress**, so some things might be a bit broken. YMMV :)

cobalt/lang/AstPrinter.java

@@ -0,0 +1,54 @@
+package cobalt.lang;
+
+// Creates an unambiguous, if ugly, string representation of AST nodes.
+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));
+    }
+}

cobalt/lang/Cobalt.java

@@ -0,0 +1,91 @@
+package cobalt.lang;
+
+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 Cobalt {
+
+    private static final Interpreter interpreter = new Interpreter();
+
+    static boolean hadError = false;
+    static boolean hadRuntimeError = false;
+
+    public static void main(String[] args) throws IOException {
+        if (args.length > 1) {
+            System.out.println("Usage: cobalt [script]");
+            System.exit(64);
+        } else if (args.length == 1) {
+            runFile(args[0]);
+        } else {
+            System.out.println("Cobalt v0.1.0");
+            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);
+        if (hadRuntimeError) System.exit(70);
+    }
+
+
+    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();
+        Parser parser = new Parser(tokens);
+        List<Stmt> statements = parser.parse();
+
+        if (hadError) return;
+
+        //System.out.println(new AstPrinter().print(expression));
+        interpreter.interpret(statements);
+    }
+
+
+    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;
+    }
+
+
+    static void error(Token token, String message) {
+        if (token.type == TokenType.EOF) {
+            report(token.line, " at end", message);
+        } else {
+            report(token.line, " at '" + token.lexeme + "'", message);
+        }
+    }
+
+    static void runtimeError(RuntimeError error) {
+        System.err.println("[line " + error.token.line + "] " + error.getMessage());
+        hadRuntimeError = true;
+    }
+}

cobalt/lang/Environment.java

@@ -0,0 +1,54 @@
+package cobalt.lang;
+
+import java.util.HashMap;
+import java.util.Map;
+
+class Environment {
+    final Environment enclosing;
+    private final Map<String, Object> values = new HashMap<>();
+
+
+    Environment() {
+        enclosing = null;
+    }
+
+    Environment(Environment enclosing) {
+        this.enclosing = enclosing;
+    }
+
+
+    Object get(Token name) {
+        if (values.containsKey(name.lexeme)) {
+            return values.get(name.lexeme);
+        }
+
+        if (enclosing != null) return enclosing.get(name);
+
+        throw new RuntimeError(name,
+            "Undefined reference to variable: '" + name.lexeme + "'.");
+    }
+
+    void define(Token name, Object value) {
+        if (!values.containsKey(name.lexeme)) {
+            values.put(name.lexeme, value);
+        } else {
+            throw new RuntimeError(name,
+                "Undefined reference to variable: '" + name.lexeme + "'.");
+        }
+    }
+
+    void assign(Token name, Object value) {
+        if (values.containsKey(name.lexeme)) {
+            values.put(name.lexeme, value); 
+            return;
+        }
+
+        if (enclosing != null) {
+            enclosing.assign(name, value);
+            return;
+        }
+
+        throw new RuntimeError(name,
+            "Undefined variable '" + name.lexeme + "'.");
+    }
+}

cobalt/lang/Expr.java

@@ -0,0 +1,102 @@
+package cobalt.lang;
+
+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);
+        R visitVarExpr(Variable expr);
+        R visitAssignExpr(Assign expr);
+    }
+
+
+    static class Binary extends Expr {
+        Binary(Expr left, Token operator, Expr right) {
+            this.left = left;
+            this.operator = operator;
+            this.right = right;
+        }
+
+        <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;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitGroupingExpr(this);
+        }
+
+        final Expr expression;
+    }
+
+
+    static class Literal extends Expr {
+        Literal(Object value) {
+            this.value = value;
+        }
+
+        <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;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitUnaryExpr(this);
+        }
+
+        final Token operator;
+        final Expr right;
+    }
+
+    static class Variable extends Expr {
+        Variable(Token name, boolean nullable) {
+            this.name = name;
+            this.nullable = nullable;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitVarExpr(this);
+        }
+
+        final Token name;
+        final boolean nullable;
+    }
+
+    static class Assign extends Expr {
+        Assign(Token name, Expr value) {
+            this.name = name;
+            this.value = value;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitAssignExpr(this);
+        }
+
+        final Token name;
+        final Expr value;
+    }
+
+    abstract <R> R accept(Visitor<R> visitor);
+}

cobalt/lang/Interpreter.java

@@ -0,0 +1,250 @@
+package cobalt.lang;
+
+import java.util.List;
+
+class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
+
+    private Environment environment = new Environment();
+
+    void interpret(List<Stmt> statements) {
+        try {
+            for (Stmt statement : statements) {
+                execute(statement);
+            }
+        } catch(RuntimeError error) {
+            Cobalt.runtimeError(error);
+        }
+    }
+
+    @Override
+    public Object visitLiteralExpr(Expr.Literal expr) {
+        return expr.value;
+    }
+
+    @Override
+    public Object visitUnaryExpr(Expr.Unary expr) {
+        Object right = evaluate(expr.right);
+
+        switch (expr.operator.type) {
+            case BANG:
+                return !isTruthy(right);
+            case MINUS:
+                return -(double) right;
+        }
+
+        return null;
+    }
+
+    @Override
+    public Object visitVarExpr(Expr.Variable expr) {
+        // TODO: Fix analogous variable issues
+        return environment.get(expr.name);
+        // Object var_value = environment.get(expr.name);
+        // if (var_value != null) {
+        //     return environment.get(expr.name);
+        // } else {
+        //     throw new RuntimeError(expr.name,
+        //         "Reference to undefined variable: '" + expr.name + "'.");
+        // }
+    }
+
+    private boolean isTruthy(Object object) {
+        if (object == null)
+            return false;
+        if (object instanceof Boolean)
+            return (boolean) object;
+        return true;
+    }
+
+    @Override
+    public Object visitGroupingExpr(Expr.Grouping expr) {
+        return evaluate(expr.expression);
+    }
+
+    private Object evaluate(Expr expr) {
+        return expr.accept(this);
+    }
+
+    private void execute(Stmt stmt) {
+        stmt.accept(this);
+    }
+
+    private void executeBlock(List<Stmt> statements,
+                              Environment environment) {
+        Environment previous = this.environment;
+        try {
+            this.environment = environment;
+
+            for (Stmt statement : statements) {
+                execute(statement);
+            }
+        } finally {
+            this.environment = previous;
+        }
+    }
+
+    @Override
+    public Void visitBlockStmt(Stmt.Block stmt) {
+        executeBlock(stmt.statements, new Environment(environment));
+        return null;
+    }
+
+    @Override
+    public Void visitExpressionStmt(Stmt.Expression stmt) {
+        evaluate(stmt.expression);
+        return null;
+    }
+
+    @Override
+    public Void visitPrintStmt(Stmt.Print stmt) {
+        Object value = evaluate(stmt.expression);
+        System.out.println(stringify(value));
+        return null;
+    }
+
+    @Override
+    public Void visitVarStmt(Stmt.Var stmt) {
+        Object value = null;
+        if (stmt.initializer != null) {
+            value = evaluate(stmt.initializer);
+        }
+
+        if (!stmt.nullable && value == null) {
+            throw new RuntimeError(stmt.name, "Assignment of 'nil' to non-nullable type");
+        } else {
+            environment.define(stmt.name, value);
+            return null;
+        }
+    }
+
+    @Override
+    public Object visitAssignExpr(Expr.Assign expr) {
+        Object value = evaluate(expr.value);
+        environment.assign(expr.name, value);
+        return value;
+    }
+
+    @Override
+    public Object visitBinaryExpr(Expr.Binary expr) {
+        Object left = evaluate(expr.left);
+        Object right = evaluate(expr.right);
+
+        switch (expr.operator.type) {
+            case GREATER:
+                checkNumberOperands(expr.operator, left, right);
+                return (double) left > (double) right;
+            case LESS:
+                checkNumberOperands(expr.operator, left, right);
+                return (double) left < (double) right;
+            case GREATER_EQUAL:
+                checkNumberOperands(expr.operator, left, right);
+                return (double) left >= (double) right;
+            case LESS_EQUAL:
+                checkNumberOperands(expr.operator, left, right);
+                return (double) left <= (double) right;
+            case BANG_EQUAL:
+                checkNumberOperands(expr.operator, left, right);
+                return !isEqual(left, right);
+            case EQUAL_EQUAL:
+                checkNumberOperands(expr.operator, left, right);
+                return isEqual(left, right);
+            case MINUS:
+                checkNumberOperand(expr.operator, right);
+                return (double) left - (double) right;
+            case PLUS:
+                if (left instanceof Double && right instanceof Double) {
+                    return (double) left + (double) right;
+                } else if (left instanceof String && right instanceof String) {
+                    return (String) left + (String) right;
+                } else if (left instanceof String && right instanceof Double) {
+                    return (String) left + (Double) right;
+                } else if (left instanceof Double && right instanceof String) {
+                    return (Double) left + (String) right;
+                } else if ((left == null) && right instanceof String) {
+                    return "nil" + (String) right;
+                } else if (left instanceof String && (right == null)) {
+                    return (String) left + "nil";
+                }
+                throw new RuntimeError(expr.operator, "Invalid operands: '" + left + "' and '" + right + "'");
+            case SLASH:
+                checkNumberOperands(expr.operator, left, right);
+                checkNumberOperand(expr.operator, right);
+                return (double) left / (double) right;
+            case STAR:
+                checkNumberOperands(expr.operator, left, right);
+                boolean usingStrings = false;
+                String val = "";
+                double limit = 0;
+
+                if (left instanceof String) {
+                    usingStrings = true;
+                    val = (String)left;
+                    limit = (Double)right;
+                } else if (right instanceof String) {
+                    usingStrings = true;
+                    val = (String)right;
+                    limit = (Double)left;
+                }
+
+                if (usingStrings) {
+                    String output = "";
+                    for (int i = 0; i < limit; i++) {
+                        output += val;
+                    }
+                    return output;
+                } else {
+                    return (double) left * (double) right;
+                }
+        }
+
+        // Unreachable
+        return null;
+    }
+
+    private boolean isEqual(Object a, Object b) {
+        if (a == null && b == null)
+            return true;
+        if (a == null)
+            return false;
+
+        return a.equals(b);
+    }
+
+    private String stringify(Object object) {
+        if (object == null) return "nil";
+
+        if (object instanceof Double) {
+            String text = object.toString();
+            if (text.endsWith(".0")) {
+                text = text.substring(0, text.length() - 2);
+            }
+            return text;
+        }
+
+        return object.toString();
+    }
+
+    private void checkNumberOperand(Token operator, Object operand) {
+        if (operand instanceof Double) {
+            if (operator.type == TokenType.SLASH && (double)operand == 0) {
+                throw new RuntimeError(operator, "Division by zero is not allowed");
+            }
+            return;
+        }
+        throw new RuntimeError(operator, "Operand must be a number");
+    }
+
+    private void checkNumberOperands(Token operator, Object left, Object right) {
+        if (left instanceof Double && right instanceof Double) {
+            return;
+        }
+        if (left instanceof String && right instanceof Double) {
+            return;
+        }
+        if (left instanceof Double && right instanceof String) {
+            return;
+        }
+        
+        throw new RuntimeError(operator, "Operands must be numbers");
+    }
+}

cobalt/lang/Parser.java

@@ -0,0 +1,315 @@
+package cobalt.lang;
+
+import java.util.List;
+
+import cobalt.lang.Expr.Variable;
+
+import java.util.ArrayList;
+import static cobalt.lang.TokenType.*;
+
+class Parser {
+    private static class ParseError extends RuntimeException {}
+
+    private final List<Token> tokens;
+    private int current = 0;
+
+    Parser(List<Token> tokens) {
+        this.tokens = tokens;
+    }
+
+
+    List<Stmt> parse() {
+        List<Stmt> statements = new ArrayList<>();
+        while (!isAtEnd()) {
+            statements.add(declaration());
+        }
+
+        return statements;
+    }
+
+
+    private Expr expression() {
+        return assignment();
+    }
+
+
+    private Stmt declaration() {
+        try {
+            if (match(VAR)) return varDeclaration();
+            return statement();
+        } catch (ParseError error) {
+            synchronize();
+            return null;
+        }
+    }
+
+    
+    private Stmt statement() {
+        if (match(PRINT)) return printStatement();
+        if (match(LEFT_BRACE)) return new Stmt.Block(block());
+
+        return expressionStatement();
+    }
+
+
+    private Stmt printStatement() {
+        Expr value = expression();
+        consume(SEMICOLON, "Expected ';' after value.");
+        return new Stmt.Print(value);
+    }
+
+
+    private Stmt varDeclaration() {
+        Token name = consume(IDENTIFIER, "Expected variable name.");
+
+        Expr initializer = null;
+        boolean nullable = false;
+        
+        if (match(NULLABLE)) {
+            nullable = true;
+        }
+
+        if (match(EQUAL)) {
+            initializer = expression();
+        }
+
+        consume(SEMICOLON, "Expected ';' after variable declaration.");
+
+        return new Stmt.Var(name, nullable, initializer);
+    }
+
+
+    private Stmt expressionStatement() {
+        Expr expr = expression();
+        consume(SEMICOLON, "Expected ';' after value.");
+        return new Stmt.Expression(expr);
+    }
+
+
+    private List<Stmt> block() {
+        List<Stmt> statements = new ArrayList<>();
+
+        while (!check(RIGHT_BRACE) && !isAtEnd()) {
+            statements.add(declaration());
+        }
+
+        consume(RIGHT_BRACE, "Expected '}' after block.");
+        return statements;
+    }
+
+
+    private Expr assignment() {
+        Expr expr = equality();
+
+        if (match(EQUAL)) {
+            Token equals = previous();
+            Expr value = assignment();
+
+            if (expr instanceof Expr.Variable) {
+                Variable var = (Expr.Variable) expr;
+                Token name = var.name;
+                if (!var.nullable && value == null) {
+                    error(equals, "Invalid assignment of 'nil' on non-nullable type");
+                } else {
+                    return new Expr.Assign(name, value);
+                }
+            }
+            error(equals, "Invalid assignment on non-variable type");
+        }
+
+        return expr;
+    }
+
+    // Parser definition for handling equalities
+    //
+    // equality     ->  comparison ( ( "!=" | "==" ) comparison )* ;
+    //
+    private Expr equality() {
+        Expr expr = comparison();
+        while (match(BANG_EQUAL, EQUAL_EQUAL)) {
+            Token operator = previous();
+            Expr right = comparison();
+            expr = new Expr.Binary(expr, operator, right);
+        }
+
+        return expr;
+    }
+
+
+    // Parser definition for handling comparisons
+    //
+    // comparison   ->  term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
+    //
+    private Expr comparison() {
+        Expr expr = term();
+
+        while (match(GREATER, GREATER_EQUAL, LESS, LESS_EQUAL)) {
+            Token operator = previous();
+            Expr right = term();
+            expr = new Expr.Binary(expr, operator, right);
+        }
+
+        return expr;
+    }
+
+
+    private Expr term() {
+        Expr expr = factor();
+
+        while (match(MINUS, PLUS)) {
+            Token operator = previous();
+            Expr right = factor();
+            expr = new Expr.Binary(expr, operator, right);
+        }
+
+        return expr;
+    }
+
+
+    private Expr factor() {
+        Expr expr = unary();
+
+        while (match(SLASH, STAR)) {
+            Token operator = previous();
+            Expr right = unary();
+            expr = new Expr.Binary(expr, operator, right);
+        }
+
+        return expr;
+    }
+
+    
+    // Parser definition for handling unary statements
+    //
+    // unary   ->  ( "!" | "-" ) unary
+    //             | primary ;
+    //
+    private Expr unary() {
+        if (match(BANG, MINUS)) {
+            Token operator = previous();
+            Expr right = unary();
+            return new Expr.Unary(operator, right);
+        }
+
+        return primary();
+    }
+
+
+    // Parser definition for handling primary statements
+    //
+    // primary   ->  NUMBER | STRING | "true" | "false" | "nil"
+    //             | "(" expression ")" ;
+    //
+    private Expr primary() {
+        if (match(FALSE)) return new Expr.Literal(false);
+        if (match(TRUE)) return new Expr.Literal(true);
+        if (match(NIL)) return new Expr.Literal(null);
+
+        if (match(NUMBER, STRING)) {
+            return new Expr.Literal(previous().literal);
+        }
+
+        if (match(IDENTIFIER)) {
+            if (match(NULLABLE)) {
+                return new Expr.Variable(previous(), true);
+            } else {
+                return new Expr.Variable(previous(), false);
+            }
+        }
+
+        if (match(LEFT_PAREN)) {
+            Expr expr = expression();
+            consume(RIGHT_PAREN, "Expect ')' after expression.");
+            return new Expr.Grouping(expr);
+        }
+
+        throw error(peek(), "Expected expression.");
+    }
+
+
+    // Checks to see if the current token has any of the given types. If so,
+    // it consumes the token and returns true. Otherwise, it returns false and leaves
+    // the current token alone.
+    private boolean match(TokenType... types) {
+        for (TokenType type : types) {
+            if (check(type)) {
+                advance();
+                return true;
+            }
+        }
+        return false;
+    }
+
+
+    // Consume function
+    private Token consume(TokenType type, String message) {
+        if (check(type)) return advance();
+
+        throw error(peek(), message);
+    }
+
+
+    // Returns true if the current token is of the given type, false if otherwise
+    private boolean check(TokenType type) {
+        if (isAtEnd()) return false;
+        return peek().type == type;
+    }
+
+
+    // Consume the current token and return it
+    private Token advance() {
+        if (!isAtEnd()) current++;
+        return previous();
+    }
+
+
+    // Check to see if we've run out of tokens to parse
+    private boolean isAtEnd() {
+        return peek().type == EOF;
+    }
+
+
+    // Return the current token we have yet to consume
+    private Token peek() {
+        return tokens.get(current);
+    }
+
+
+    // Return the previous token we just consumed
+    private Token previous() {
+        return tokens.get(current - 1);
+    }
+
+
+    // Throw a new parse error based on the incorrect token
+    private ParseError error(Token token, String message) {
+        Cobalt.error(token, message);
+        return new ParseError();
+    }
+
+
+    // Once finding a parse error, discard the rest of the tokens in 
+    // a statement in order to prevent cascading errors.
+    private void synchronize() {
+        advance();
+        while (!isAtEnd()) {
+            if (previous().type == SEMICOLON) return;
+
+            switch (peek().type) {
+                case CLASS:
+                case FOR:
+                case FUNC:
+                case IF:
+                case PRINT:
+                case RETURN:
+                case VAR:
+                case WHILE:
+                return;
+            }
+
+            advance();
+        }
+    }
+}
+
+

cobalt/lang/RuntimeError.java

@@ -0,0 +1,10 @@
+package cobalt.lang;
+
+class RuntimeError extends RuntimeException {
+    final Token token;
+
+    RuntimeError(Token token, String message) {
+        super(message);
+        this.token = token;
+    }
+}

cobalt/lang/Scanner.java

@@ -0,0 +1,318 @@
+package cobalt.lang;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static cobalt.lang.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 = 0;
+    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("func", FUNC);
+        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);
+    }
+
+    // Constructor
+    // Set our source string to be the incoming character data from the
+    // input script
+    Scanner(String source) {
+        this.source = source;
+    }
+
+    // Scan the input file for all available tokens, return a Token list with all
+    // of our valid tokens
+    List<Token> scanTokens() {
+        while (!isAtEnd()) {
+            start = current;
+            scanToken();
+        }
+
+        tokens.add(new Token(EOF, "", null, line));
+        return tokens;
+    }
+
+    // Check to see if we have reached the end of the script
+    private boolean isAtEnd() {
+        return current >= source.length();
+    }
+
+    // Parse the current token from the scanner to see if its a valid
+    // lexeme. Report an error otherwise
+    private void scanToken() {
+        char c = advance();
+        switch (c) {
+            // Structural and Accessors
+            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(SEMICOLON); break;
+
+            // Operators 
+            case '*': addToken(STAR); break;
+            case '-': addToken(MINUS); break;
+            case '+': addToken(PLUS); 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 '/': addToken(SLASH); break;
+            case '?': addToken(NULLABLE); break;
+    
+            // Comments
+            case '#': 
+                // A comment goes until the end of the line
+                while (peek() != '\n' && !isAtEnd()) advance();
+                break;
+    
+
+            // Whitespace and new lines
+            case ' ':
+            case '\r':
+            case '\t':
+                //ignore whitespace characters
+                break;
+            case '\n':
+                line++;
+                break;
+
+            case '"':
+                string();
+                break;
+
+            default:
+                if (isDigit(c)) {
+                    // Check to see if our incoming value is part of a number
+                    // Switch on base prefix (hex, binary, base10...)
+                    switch (peek()) {
+                        case 'x':
+                            advance(); // Advance to disregard the '0x' prefix
+                            hex();
+                            break;
+                        case 'b':
+                            advance(); // Advance to disregard the '0b' prefix
+                            binary();
+                            break;
+                        case 'o':
+                            advance(); // Advance to disregard the '0o' prefix
+                            octal();
+                            break;
+                        default:
+                            number();
+                            break;
+                    }
+                } else if (isAlpha(c)) {
+                    // Check to see if our incoming value is part of
+                    // a reserved word or identifier
+                    identifier();
+                } else {
+                    Cobalt.error(line, "Unexpected character.");
+                }
+                break;
+        }
+    }
+
+
+    // Determine if the char is a base 10 digit
+    private boolean isDigit(char c) {
+        return c >= '0' && c <= '9';
+    }
+
+
+    // Determine if the character is a valid base 16 digit
+    private boolean isHex(char c) {
+        return (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f');
+    }
+
+
+    // Determine if the character is a valid base 16 digit
+    private boolean isBinary(char c) {
+        return (c >= '0' && c <= '1');
+    }
+
+
+    // Determine if the character is a valid base 8 digit
+    private boolean isOctal(char c) {
+        return (c >= '0' && c <= '7');
+    }
+
+
+    // Parse and tokenize the value as a base 10 number
+    private void number() {
+        while (isDigit(peek())) advance();
+
+        // Look for a decimal place.
+        if (peek() == '.' && isDigit(peekNext())) {
+            // Consume the .
+            advance();
+
+            while (isDigit(peek())) advance();
+        }
+        
+        addToken(NUMBER, Double.parseDouble(source.substring(start, current)));
+    }
+
+
+    // Parse and tokenize the value as a hexadecimal number, store in base 10
+    private void hex() {
+        while (isDigit(peek()) || isHex(peek())) advance();
+        
+        addToken(NUMBER, Long.parseLong(source.substring(start + 2, current), 16));
+    }
+
+
+    // Parse and tokenize the value as a binary number, store in base 10
+    private void binary() {
+        while (isBinary(peek())) advance();
+        
+        addToken(NUMBER, Long.parseLong(source.substring(start + 2, current), 2));
+    }
+
+
+    // Parse and tokenize the value as an octal number, store in base 10
+    private void octal() {
+        while (isOctal(peek())) advance();
+        
+        addToken(NUMBER, Long.parseLong(source.substring(start + 2, current), 8));
+    }
+
+
+    // TODO: Lox spec supports multiline strings, we'll need to
+    // probably remove that support since I don't intend Cobalt's
+    // grammar to support that (maybe) :/
+
+    // TODO: Escape sequences are not supported atm, for the
+    // love of god please implement this functionality. Probably
+    // should make an enum for the valid escape sequences, parse them
+    // out like we do with operators, and inject the actual escape
+    // sequence in the object thats returned to the interpreter
+
+    // Process the input line if quotation marks are found
+    // and we have a string literal
+    private void string() {
+        while (peek() != '"' && !isAtEnd()) {
+            if (peek() == '\n') line++;
+            advance();
+        }
+
+        if (isAtEnd()) {
+            Cobalt.error(line, "Unterminated string.");
+            return;
+        }
+
+        // Get closing quotes
+        advance();
+
+        // Trim the
+        String value = source.substring(start + 1, current - 1);
+        addToken(STRING, value);
+    }
+
+
+    // Determine if the infoming token is alphanumeric, and
+    // add it to the Token list if it is valid
+    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);
+    }
+
+
+    // Checkout the next character in our input, but dont consume it
+    // This is mainly to process things like comments that take an entire line
+    private char peek() {
+        if (isAtEnd()) return '\0';
+        return source.charAt(current);
+    }
+
+
+    // Checkout the next+1 character in our input, but dont consume it
+    // This is mainly to process things like comments that take an entire line
+    private char peekNext() {
+        if (current + 1 >= source.length()) return '\0';
+        return source.charAt(current + 1);
+    }
+
+
+    // Check to see if the character passed is within
+    // [a-z][A-Z]
+    private boolean isAlpha(char c) {
+        return (c >= 'a' && c <= 'z') ||
+               (c >= 'A' && c <= 'Z') ||
+               c == '_';
+    }
+
+
+    // Check to see if the character passed is within
+    // [a-z][A-Z][0-9]
+    private boolean isAlphaNumeric(char c) {
+        return isAlpha(c) || isDigit(c);
+    }
+
+
+    // Return a boolean based on if a char is found at the current cursor,
+    // then increment
+    private boolean match(char expected) {
+        if (isAtEnd()) return false;
+        if (source.charAt(current) != expected) return false;
+
+        current++;
+        return true;
+    }
+
+
+    // Advance the char pointer in the line scanner
+    private char advance() {
+        return source.charAt(current++);
+    }
+
+
+    // Add a token to the token List that does not have an object literal
+    // associated with it.
+    private void addToken(TokenType type) {
+        addToken(type, null);
+    }
+
+
+    // Add a token to the token List that has an object associated with it
+    private void addToken(TokenType type, Object literal) {
+        String text = source.substring(start, current);
+        tokens.add(new Token(type, text, literal, line));
+    }
+}

cobalt/lang/Stmt.java

@@ -0,0 +1,65 @@
+package cobalt.lang;
+
+import java.util.List;
+
+abstract class Stmt {
+    interface Visitor<R> {
+        R visitBlockStmt(Block stmt);
+        R visitExpressionStmt(Expression stmt);
+        R visitPrintStmt(Print stmt);
+        R visitVarStmt(Var stmt);
+    }
+
+    static class Block extends Stmt {
+        Block(List<Stmt> statements) {
+            this.statements = statements;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitBlockStmt(this);
+        }
+
+        final List<Stmt> statements;
+    }
+
+    static class Expression extends Stmt {
+        Expression(Expr expression) {
+            this.expression = expression;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitExpressionStmt(this);
+        }
+
+        final Expr expression;
+    }
+    static class Print extends Stmt {
+        Print(Expr expression) {
+            this.expression = expression;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitPrintStmt(this);
+        }
+
+        final Expr expression;
+    }
+    
+    static class Var extends Stmt {
+        Var(Token name, boolean nullable, Expr initializer) {
+            this.name = name;
+            this.nullable = nullable;
+            this.initializer = initializer;
+        }
+
+        <R> R accept(Visitor<R> visitor) {
+            return visitor.visitVarStmt(this);
+        }
+
+        final Token name;
+        final boolean nullable;
+        final Expr initializer;
+    }
+
+    abstract <R> R accept(Visitor<R> visitor);
+}

cobalt/lang/Token.java

@@ -0,0 +1,19 @@
+package cobalt.lang;
+
+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;
+    }
+}

cobalt/lang/TokenType.java

@@ -0,0 +1,20 @@
+package cobalt.lang;
+
+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, NULLABLE,
+
+    // Literals
+    IDENTIFIER, STRING, NUMBER,
+
+    // Keywords
+    AND, CLASS, ELSE, FALSE, FUNC, FOR, IF, NIL, OR,
+    PRINT, RETURN, SUPER, THIS, TRUE, VAR, WHILE,
+
+    EOF
+}

cobalt/tool/GenerateAst.java

@@ -0,0 +1,101 @@
+package cobalt.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(1);
+        }
+        String outputDir = args[0];
+
+        defineAst(outputDir, "Expr", Arrays.asList(
+            "Assign   : Token name, Expr value",
+            "Binary   : Expr left, Token operator, Expr right",
+            "Grouping : Expr expression",
+            "Literal  : Object value",
+            "Variable : Token Name",
+            "Unary    : Token operator, Expr right",
+            "Variable : Token name"
+        ));
+
+        defineAst(outputDir, "Stmt", Arrays.asList(
+            "Block      : List<Stmt> statements",
+            "Expression : Expr expression",
+            "Print      : Expr expression",
+            "Var        : Token name, Expr initializer"
+        ));
+    }
+
+    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 classes.
+        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("");
+        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("    }");
+    }
+
+    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("        <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("    }");
+    }
+}

compile

@@ -1,3 +0,0 @@
-#!/bin/bash
-
-g++ parser.cpp lexer.cpp main.cpp -o main

examples/test.cobalt

@@ -0,0 +1,25 @@
+# Statement tests
+print "These are statement tests for Cobalt!";
+print 10 + 12;
+print 13 + (14 - 7) * 3;
+print "Hello, " + "World!";
+print "String " + "Multiplication " * 3;
+
+# Variable declaration
+var a = 10;
+print ("a is " + a);
+
+# Nullable variable declaration
+var b? = nil;
+print ("b is " + b);
+
+# Examples of structured block statements with scoping
+{
+    print "we are now in a nested scope!";
+
+    # Don't really like this behaviour, as I think it should throw a runtime error
+    # Instead it pulls a's state of 10 in the upper environment block
+    # Still trying to resolve this...
+    var a = a + 5;
+    print ("a is " + a);
+}

include/lexer.h

@@ -1,14 +0,0 @@
-#include <iostream>
-
-#ifndef LEXER_H
-#define LEXER_H
-
-class Lexer
-{
-    private:
-        std::string extension = ".prog";
-    public:
-        Lexer(std::string &file_name);
-};
-
-#endif

include/parser.h

@@ -1,14 +0,0 @@
-#include <iostream>
-
-#ifndef PARSER_H
-#define PARSER_H
-
-class Parser
-{
-    private:
-
-    public:
-        Parser(std::string input_file);
-};
-
-#endif

lang_spec.txt

@@ -0,0 +1,75 @@
+using cobalt.std;
+using cobalt.math;
+
+// Comments
+
+/*
+ Block Comments
+*/
+
+public class MyProgram {
+
+    // *** Instance Variables ***
+
+    // (Option 1)
+    // Since mutable variables are frequently used, you should have to specify if the variable is intended
+    // to be immutable/constant
+
+    let x: int = 0;             // Mutable type
+    let y: const int = 0;       // Immutable type
+
+
+    // (Option 2)
+    // Assume all variables are immutable, and only allow them to be mutable if specified. Helpful in compiled, memory
+    // safe languages, but probably not for an interpreted language that sits in memory?
+
+    let mut x: int = 0;         // Mutable type
+    let y: int = 0;             // Immutable type
+
+
+    // *** Main and Declaring functions ***
+    
+    // I think scripts should work similar to python, but not be as
+    // funky/verbose with function names
+
+    // If there is no main function defined within the script, the interpreter should
+    // process the file sequentially like Python,
+    // Otherwise, the main function is ran and operates like any normal program
+
+    // Best practice would have main return an integer, however it could be
+    // void or return any other type
+
+
+    // (Option 1, C/C++/Java style)
+    private int main1() {
+        // Some code
+        return 0;
+    }
+
+    // (Option 2, Swift/Rust style)
+    private func main() => int {
+        // Some code
+        return 0;
+    }
+
+    // (Option 3, Ada style)
+    private func main() returns int {
+        // Some code
+        return 0;
+    }
+
+    // *** Handling Multiple Main Methods ***
+
+    // I feel that classes should be able to have their own main methods, and it could be
+    // determined which one is the entry point by requiring the user to provide an entry point
+    // 
+    //  (Example)
+    //      -Multiple classes in one file, each with their own main method
+    //      -Specify the script along with the class when opening with Cobalt, and it will run that specific class
+    //      -Attempt to run the class's main method. Error if it doesn't exist
+    //      -If there are multiple mains and one isn't specific, just error
+    //
+    //      Ex: cobalt script.cblt --main MyClass
+    //
+    // This allows for multiple "sub programs" within a single Cobalt script
+}

makefile

@@ -1,20 +0,0 @@
-
-#OBJS specifies which files to compile as part of the project
-OBJS = $(wildcard src/*.cpp) 
-
-#CC specifies which compiler we're using
-CC = g++
-
-#COMPILER_FLAGS specifies the additional compilation options we're using
-# -w suppresses all warnings
-COMPILER_FLAGS = -w
-
-#LINKER_FLAGS specifies the libraries we're linking against
-LINKER_FLAGS = 
-
-#OBJ_NAME specifies the name of our exectuable
-OBJ_NAME = cobalt
-
-#This is the target that compiles our executable
-all : $(OBJS)
-	$(CC) $(OBJS) $(COMPILER_FLAGS) $(LINKER_FLAGS) -o $(OBJ_NAME)

script.prog

@@ -1,3 +0,0 @@
-hello world, this is a lexer test
-hello world
-Kanye's new name is Ye

src/lexer.cpp

@@ -1,30 +0,0 @@
-#include <stdio.h>
-#include <iostream>
-#include <fstream>
-#include "../include/lexer.h"
-
-char c;
-FILE* input_file;
-
-Lexer::Lexer(std::string &file_name) {
-    input_file = fopen(file_name.c_str(),"r");
-    if(input_file == nullptr) {
-        std::cout << "[Error] Script " << input_file << " could not be read\n";
-        exit(1);
-    } 
-
-    c = getc(input_file);
-    if (c == EOF) {
-        //do something related to eof here?
-        fclose(input_file);
-    }
-}
-
-char nextChar() {
-    if (c != EOF) {
-        c = getc(input_file);
-    } else {
-        c = EOF;
-    }
-    return c;
-}

src/main.cpp

@@ -1,15 +0,0 @@
-#include <stdio.h>
-#include <iostream>
-#include <vector>
-
-#include "../include/lexer.h"
-
-int main(int argc, char *argv[]) {
-    if (argc > 1) {
-        std::string file_name(argv[1]);
-        Lexer lex(file_name);
-    } else {
-        std::cout << "[Error] No input file provided\n";
-    }
-    return 0;
-}

src/parser.cpp

@@ -1,8 +0,0 @@
-#include <stdio.h>
-#include <iostream>
-
-#include "../include/parser.h"
-
-Parser::Parser(std::string input_file) {
-
-}