diff --git a/samples/addition.lox b/samples/addition.lox
new file mode 100644
index 0000000..4fc8bc9
--- /dev/null
+++ b/samples/addition.lox
@@ -0,0 +1 @@
+true+false
\ No newline at end of file
diff --git a/src/compile.zig b/src/compile.zig
new file mode 100644
index 0000000..a338362
--- /dev/null
+++ b/src/compile.zig
@@ -0,0 +1,29 @@
+const std = @import("std");
+const debug = std.debug;
+const Allocator = std.mem.Allocator;
+
+const Scanner = @import("./scanner.zig").Scanner;
+const Token = @import("./scanner.zig").Token;
+const TokenType = @import("./scanner.zig").TokenType;
+
+pub fn compile(allocator: Allocator, contents: []const u8) !void {
+    var line: ?usize = null;
+    _ = allocator;
+
+    var scanner = Scanner.init(contents);
+
+    while (true) {
+        const token = scanner.scan_token();
+        if (line == null or token.line != line.?) {
+            debug.print("{d:4} ", .{token.line});
+            line = token.line;
+        } else {
+            debug.print("   | ", .{});
+        }
+        debug.print("{s:12} len:{d:2} '{s}'\n", .{ token.token_type.string(), token.length, token.start[0..token.length] });
+
+        if (token.token_type == TokenType.EOF) {
+            break;
+        }
+    }
+}
diff --git a/src/main.zig b/src/main.zig
index 76924a0..f0c19aa 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -5,42 +5,102 @@ const Allocator = std.mem.Allocator;
 const Chunk = @import("./chunk.zig").Chunk;
 const OpCode = @import("./opcode.zig").OpCode;
 const VM = @import("./vm.zig").VM;
+const InterpretResult = @import("./vm.zig").InterpretResult;
+
+const compile = @import("./compile.zig").compile;
 
 pub const DEBUG_TRACE_EXECUTION = true;
 
+pub fn repl(allocator: Allocator) !void {
+    var line: [1024]u8 = undefined;
+
+    const stdin = std.io.getStdIn().reader();
+    const stdout = std.io.getStdOut().writer();
+
+    while (true) {
+        try stdout.print("> ", .{});
+
+        @memset(&line, 0);
+
+        const bytes_read = try stdin.read(&line);
+
+        if (bytes_read == 0) {
+            try stdout.print("\n", .{});
+            break;
+        }
+
+        _ = try interpret(allocator, &line);
+    }
+}
+
+pub fn run_file(allocator: Allocator, filepath: []const u8) !void {
+    const file = try std.fs.cwd().openFile(filepath, .{});
+    defer file.close();
+
+    const file_content = try file.readToEndAlloc(allocator, 1024 * 1024);
+    defer allocator.free(file_content);
+
+    const result = try interpret(allocator, file_content);
+
+    switch (result) {
+        InterpretResult.COMPILE_ERROR => std.process.exit(65),
+        InterpretResult.RUNTIME_ERROR => std.process.exit(70),
+        else => {},
+    }
+}
+
+pub fn interpret(allocator: Allocator, content: []const u8) !InterpretResult {
+    // XXX catch and return InterpretResult.COMPILE_ERROR ?
+    try compile(allocator, content);
+    return InterpretResult.OK;
+}
+
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{ .safety = true }){};
     defer _ = debug.assert(gpa.deinit() == .ok);
     const allocator = gpa.allocator();
 
-    var vm = VM.new(allocator);
+    const args = try std.process.argsAlloc(allocator);
+    defer std.process.argsFree(allocator, args);
 
-    var chunk = Chunk.new();
-    try chunk.init(allocator);
+    if (args.len == 1) {
+        try repl(allocator);
+    } else if (args.len == 2) {
+        try run_file(allocator, args[1]);
+    } else {
+        const stdout = std.io.getStdOut().writer();
+        try stdout.print("Usage: clox [path]\n", .{});
+        std.process.exit(64);
+    }
 
-    var constant = try chunk.add_constant(allocator, 1.2);
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_CONSTANT), 123);
-    try chunk.write(allocator, @intCast(constant), 123);
+    // var vm = VM.new(allocator);
 
-    constant = try chunk.add_constant(allocator, 3.4);
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_CONSTANT), 123);
-    try chunk.write(allocator, @intCast(constant), 123);
+    // var chunk = Chunk.new();
+    // try chunk.init(allocator);
 
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_ADD), 123);
+    // var constant = try chunk.add_constant(allocator, 1.2);
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_CONSTANT), 123);
+    // try chunk.write(allocator, @intCast(constant), 123);
 
-    constant = try chunk.add_constant(allocator, 5.6);
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_CONSTANT), 123);
-    try chunk.write(allocator, @intCast(constant), 123);
+    // constant = try chunk.add_constant(allocator, 3.4);
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_CONSTANT), 123);
+    // try chunk.write(allocator, @intCast(constant), 123);
 
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_DIVIDE), 123);
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_ADD), 123);
 
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_NEGATE), 123);
-    try chunk.write(allocator, @intFromEnum(OpCode.OP_RETURN), 123);
+    // constant = try chunk.add_constant(allocator, 5.6);
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_CONSTANT), 123);
+    // try chunk.write(allocator, @intCast(constant), 123);
 
-    chunk.dissassemble("test chunk");
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_DIVIDE), 123);
 
-    _ = try vm.interpret(&chunk);
-    vm.free();
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_NEGATE), 123);
+    // try chunk.write(allocator, @intFromEnum(OpCode.OP_RETURN), 123);
 
-    chunk.deinit(allocator);
+    // chunk.dissassemble("test chunk");
+
+    // _ = try vm.interpret(&chunk);
+    // vm.free();
+
+    // chunk.deinit(allocator);
 }
diff --git a/src/scanner.zig b/src/scanner.zig
new file mode 100644
index 0000000..a0d4070
--- /dev/null
+++ b/src/scanner.zig
@@ -0,0 +1,359 @@
+const std = @import("std");
+
+pub const TokenType = enum {
+    // 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,
+    FOR,
+    FUN,
+    IF,
+    NIL,
+    OR,
+    PRINT,
+    RETURN,
+    SUPER,
+    THIS,
+    TRUE,
+    VAR,
+    WHILE,
+    ERROR,
+    EOF,
+
+    pub fn string(self: TokenType) []const u8 {
+        return switch (self) {
+            TokenType.LEFT_PAREN => "LEFT_PAREN",
+            TokenType.RIGHT_PAREN => "RIGHT_PAREN",
+            TokenType.LEFT_BRACE => "LEFT_BRACE",
+            TokenType.RIGHT_BRACE => "RIGHT_BRACE",
+            TokenType.COMMA => "COMMA",
+            TokenType.DOT => "DOT",
+            TokenType.MINUS => "MINUS",
+            TokenType.PLUS => "PLUS",
+            TokenType.SEMICOLON => "SEMICOLON",
+            TokenType.SLASH => "SLASH",
+            TokenType.STAR => "STAR",
+            TokenType.BANG => "BANG",
+            TokenType.BANG_EQUAL => "BANG_EQUAL",
+            TokenType.EQUAL => "EQUAL",
+            TokenType.EQUAL_EQUAL => "EQUAL_EQUAL",
+            TokenType.GREATER => "GREATER",
+            TokenType.GREATER_EQUAL => "GREATER_EQUAL",
+            TokenType.LESS => "LESS",
+            TokenType.LESS_EQUAL => "LESS_EQUAL",
+            TokenType.IDENTIFIER => "IDENTIFIER",
+            TokenType.STRING => "STRING",
+            TokenType.NUMBER => "NUMBER",
+            TokenType.AND => "AND",
+            TokenType.CLASS => "CLASS",
+            TokenType.ELSE => "ELSE",
+            TokenType.FALSE => "FALSE",
+            TokenType.FOR => "FOR",
+            TokenType.FUN => "FUN",
+            TokenType.IF => "IF",
+            TokenType.NIL => "NIL",
+            TokenType.OR => "OR",
+            TokenType.PRINT => "PRINT",
+            TokenType.RETURN => "RETURN",
+            TokenType.SUPER => "SUPER",
+            TokenType.THIS => "THIS",
+            TokenType.TRUE => "TRUE",
+            TokenType.VAR => "VAR",
+            TokenType.WHILE => "WHILE",
+            TokenType.ERROR => "ERROR",
+            TokenType.EOF => "EOF",
+        };
+    }
+};
+
+pub const Token = struct {
+    token_type: TokenType,
+    start: []const u8,
+    length: usize,
+    line: usize,
+};
+
+pub const Scanner = struct {
+    source: []const u8,
+    start: usize,
+    current: usize,
+    line: usize,
+
+    pub fn init(content: []const u8) Scanner {
+        return Scanner{
+            .start = 0,
+            .current = 0,
+            .line = 1,
+            .source = content,
+        };
+    }
+
+    pub fn scan_token(self: *Scanner) Token {
+        self.skip_whitespace();
+
+        self.start = self.current;
+
+        if (self.is_at_end()) {
+            return self.make_token(TokenType.EOF);
+        }
+
+        const c = self.advance();
+        if (self.is_alpha(c)) {
+            return self.identifier();
+        }
+
+        if (self.is_digit(c)) {
+            return self.number();
+        }
+
+        return switch (c) {
+            '(' => self.make_token(TokenType.LEFT_PAREN),
+            ')' => self.make_token(TokenType.RIGHT_PAREN),
+            '{' => self.make_token(TokenType.LEFT_BRACE),
+            '}' => self.make_token(TokenType.RIGHT_BRACE),
+            ';' => self.make_token(TokenType.SEMICOLON),
+            ',' => self.make_token(TokenType.COMMA),
+            '.' => self.make_token(TokenType.DOT),
+            '-' => self.make_token(TokenType.MINUS),
+            '+' => self.make_token(TokenType.PLUS),
+            '/' => self.make_token(TokenType.SLASH),
+            '*' => self.make_token(TokenType.STAR),
+            '!' => {
+                if (self.match('=')) {
+                    return self.make_token(TokenType.BANG_EQUAL);
+                } else {
+                    return self.make_token(TokenType.BANG);
+                }
+            },
+            '=' => {
+                if (self.match('=')) {
+                    return self.make_token(TokenType.EQUAL_EQUAL);
+                } else {
+                    return self.make_token(TokenType.EQUAL);
+                }
+            },
+            '<' => {
+                if (self.match('=')) {
+                    return self.make_token(TokenType.LESS_EQUAL);
+                } else {
+                    return self.make_token(TokenType.LESS);
+                }
+            },
+            '>' => {
+                if (self.match('=')) {
+                    return self.make_token(TokenType.GREATER_EQUAL);
+                } else {
+                    return self.make_token(TokenType.GREATER);
+                }
+            },
+            '"' => return self.string(),
+            else => self.error_token("Unexpected character."),
+        };
+    }
+
+    pub fn is_at_end(self: Scanner) bool {
+        return self.source.len == self.current;
+    }
+
+    pub fn make_token(self: Scanner, token_type: TokenType) Token {
+        return Token{
+            .token_type = token_type,
+            .start = self.source[self.start..],
+            .length = self.current - self.start,
+            .line = self.line,
+        };
+    }
+
+    pub fn error_token(self: Scanner, error_message: []const u8) Token {
+        return Token{
+            .token_type = TokenType.EOF,
+            .start = error_message,
+            .length = error_message.len,
+            .line = self.line,
+        };
+    }
+
+    pub fn advance(self: *Scanner) u8 {
+        self.current += 1;
+        return self.source[self.current - 1];
+    }
+
+    pub fn match(self: *Scanner, expected: u8) bool {
+        if (self.is_at_end()) {
+            return false;
+        }
+
+        if (self.source[self.current] != expected) {
+            return false;
+        }
+
+        self.current += 1;
+        return true;
+    }
+
+    pub fn skip_whitespace(self: *Scanner) void {
+        while (!self.is_at_end()) {
+            const c = self.peek();
+            switch (c) {
+                ' ', '\r', '\t' => {
+                    _ = self.advance();
+                },
+                '\n' => {
+                    self.line += 1;
+                    _ = self.advance();
+                },
+                '/' => {
+                    if (self.peek_next() == '/') {
+                        while (self.peek() != '\n' and !self.is_at_end()) {
+                            _ = self.advance();
+                        }
+                    } else {
+                        return;
+                    }
+                },
+                else => return,
+            }
+        }
+    }
+
+    pub fn peek(self: *Scanner) u8 {
+        if (self.is_at_end()) {
+            return 0;
+        }
+
+        return self.source[self.current];
+    }
+
+    pub fn peek_next(self: *Scanner) u8 {
+        if (self.is_at_end()) {
+            return 0;
+        }
+
+        return self.source[self.current + 1];
+    }
+
+    pub fn string(self: *Scanner) Token {
+        while (self.peek() != '"' and !self.is_at_end()) {
+            if (self.peek() == '\n') {
+                self.line += 1;
+            }
+            _ = self.advance();
+        }
+
+        if (self.is_at_end()) {
+            return self.error_token("Unterminated string.");
+        }
+
+        _ = self.advance();
+
+        return self.make_token(TokenType.STRING);
+    }
+
+    pub fn is_digit(self: Scanner, c: u8) bool {
+        _ = self;
+        return c >= '0' and c <= '9';
+    }
+
+    pub fn number(self: *Scanner) Token {
+        while (self.is_digit(self.peek())) {
+            _ = self.advance();
+        }
+
+        if (self.peek() == '.' and self.is_digit(self.peek_next())) {
+            // consume the '.'
+            _ = self.advance();
+        }
+
+        while (self.is_digit(self.peek())) {
+            _ = self.advance();
+        }
+
+        return self.make_token(TokenType.NUMBER);
+    }
+
+    pub fn is_alpha(self: Scanner, c: u8) bool {
+        _ = self;
+        return (c >= 'a' and c <= 'z') or (c >= 'A' and c <= 'Z') or c == '_';
+    }
+
+    pub fn identifier(self: *Scanner) Token {
+        while (self.is_alpha(self.peek()) or self.is_digit(self.peek())) {
+            _ = self.advance();
+        }
+
+        return self.make_token(self.identifier_type());
+    }
+
+    pub fn identifier_type(self: *Scanner) TokenType {
+        return switch (self.source[self.start]) {
+            'a' => self.check_keyword(1, 2, "nd", TokenType.AND),
+            'c' => self.check_keyword(1, 4, "class", TokenType.CLASS),
+            'e' => self.check_keyword(1, 3, "lse", TokenType.ELSE),
+            'f' => if (self.current - self.start > 1) {
+                return switch (self.source[self.start + 1]) {
+                    'a' => self.check_keyword(2, 3, "lse", TokenType.FALSE),
+                    'o' => self.check_keyword(2, 1, "r", TokenType.FOR),
+                    'u' => self.check_keyword(2, 1, "n", TokenType.FUN),
+                    else => TokenType.IDENTIFIER,
+                };
+            } else {
+                return TokenType.IDENTIFIER;
+            },
+            'i' => self.check_keyword(1, 1, "f", TokenType.IF),
+            'n' => self.check_keyword(1, 2, "il", TokenType.NIL),
+            'o' => self.check_keyword(1, 1, "or", TokenType.OR),
+            'p' => self.check_keyword(1, 4, "rint", TokenType.PRINT),
+            'r' => self.check_keyword(1, 5, "eturn", TokenType.RETURN),
+            's' => self.check_keyword(1, 4, "uper", TokenType.SUPER),
+            't' => if (self.current - self.start > 1) {
+                return switch (self.source[self.start + 1]) {
+                    'h' => self.check_keyword(2, 2, "is", TokenType.THIS),
+                    'r' => self.check_keyword(2, 2, "ue", TokenType.TRUE),
+                    else => TokenType.IDENTIFIER,
+                };
+            } else {
+                return TokenType.IDENTIFIER;
+            },
+            'v' => self.check_keyword(1, 2, "ar", TokenType.VAR),
+            'w' => self.check_keyword(1, 4, "hile", TokenType.WHILE),
+            else => TokenType.IDENTIFIER,
+        };
+    }
+
+    pub fn check_keyword(self: *Scanner, start: usize, length: usize, rest: []const u8, token_type: TokenType) TokenType {
+        if (self.current - self.start == start + length and std.mem.eql(u8, rest, self.source[self.start + start .. self.start + start + length])) {
+            return token_type;
+        }
+
+        return TokenType.IDENTIFIER;
+    }
+};
diff --git a/src/vm.zig b/src/vm.zig
index 3547969..b7139ed 100644
--- a/src/vm.zig
+++ b/src/vm.zig
@@ -12,7 +12,7 @@ const print_value = @import("./values.zig").print_value;
 
 const STACK_MAX = 256;
 
-const InterpretResult = enum {
+pub const InterpretResult = enum {
     OK,
     COMPILE_ERROR,
     RUNTIME_ERROR,
@@ -66,8 +66,8 @@ pub const VM = struct {
                 },
                 @intFromEnum(OpCode.OP_ADD) => self.binary_op(OpCode.OP_ADD),
                 @intFromEnum(OpCode.OP_SUBSTRACT) => self.binary_op(OpCode.OP_SUBSTRACT),
-                @intFromEnum(OpCode.OP_MULTIPLY) => self.binary_op(OpCode.OP_SUBSTRACT),
-                @intFromEnum(OpCode.OP_DIVIDE) => self.binary_op(OpCode.OP_SUBSTRACT),
+                @intFromEnum(OpCode.OP_MULTIPLY) => self.binary_op(OpCode.OP_MULTIPLY),
+                @intFromEnum(OpCode.OP_DIVIDE) => self.binary_op(OpCode.OP_DIVIDE),
                 @intFromEnum(OpCode.OP_NEGATE) => {
                     try self.push(-self.pop());
                 },