diff --git a/src/main.zig b/src/main.zig
index 40d72e9..71cfd6b 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,8 +1,35 @@
 const std = @import("std");
 
 const Allocator = std.mem.Allocator;
+const Scanner = @import("scanner.zig").Scanner;
 
-fn run(data: []u8) void {}
+pub var hadError = false;
+
+fn run(allocator: *Allocator, data: []u8) !void {
+    var stdout_file = try std.io.getStdOut();
+    const stdout = &stdout_file.outStream().stream;
+
+    var scanner = Scanner.init(allocator, data);
+    var tokens = try scanner.scanTokens();
+    var it = tokens.iterator();
+
+    while (it.next()) |token| {
+        try token.Simple.printToken(stdout);
+        hadError = false;
+    }
+}
+
+pub fn doError(line: usize, message: []const u8) !void {
+    try errorReport(line, "", message);
+}
+
+pub fn errorReport(line: usize, where: []const u8, message: []const u8) !void {
+    var stdout_file = try std.io.getStdOut();
+    const stdout = &stdout_file.outStream().stream;
+
+    try stdout.print("[line {}] Error {}: {}\n", line, where, message);
+    hadError = true;
+}
 
 fn runFile(allocator: *Allocator, path: []const u8) !void {
     var lox_file = try std.fs.File.openRead(path);
@@ -12,7 +39,8 @@ fn runFile(allocator: *Allocator, path: []const u8) !void {
     var slice = try allocator.alloc(u8, total_bytes);
     _ = try lox_file.read(slice);
 
-    run(slice);
+    try run(allocator, slice);
+    if (hadError) std.os.exit(65);
 }
 
 fn runPrompt(allocator: *Allocator) !void {
@@ -28,7 +56,7 @@ fn runPrompt(allocator: *Allocator) !void {
             return err;
         };
 
-        run(line);
+        try run(allocator, line);
     }
 }
 
diff --git a/src/scanner.zig b/src/scanner.zig
new file mode 100644
index 0000000..c4f9100
--- /dev/null
+++ b/src/scanner.zig
@@ -0,0 +1,93 @@
+const std = @import("std");
+
+const token = @import("token.zig");
+const main = @import("main.zig");
+
+const TokenList = std.ArrayList(token.Token);
+
+pub const Scanner = struct {
+    source: []u8,
+    tokens: TokenList,
+
+    start: usize = 0,
+    current: usize = 0,
+    line: usize = 1,
+
+    pub fn init(allocator: *std.mem.Allocator, data: []u8) Scanner {
+        return Scanner{
+            .source = data,
+            .tokens = TokenList.init(allocator),
+        };
+    }
+
+    fn isAtEnd(self: *Scanner) bool {
+        return self.current >= self.source.len;
+    }
+
+    fn advance(self: *Scanner) u8 {
+        self.current += 1;
+        return self.source[self.current - 1];
+    }
+
+    fn currentLexeme(self: *Scanner) []u8 {
+        return self.source[self.start..self.current];
+    }
+
+    fn addSimpleToken(self: *Scanner, ttype: token.TokenType) !void {
+        try self.addToken(token.Token{
+            .Simple = token.SimpleToken.init(
+                ttype,
+                self.currentLexeme(),
+                self.line,
+                {},
+            ),
+        });
+    }
+
+    fn addToken(
+        self: *Scanner,
+        tok: token.Token,
+    ) !void {
+        try self.tokens.append(tok);
+    }
+
+    fn scanToken(self: *Scanner) !void {
+        var c = self.advance();
+
+        switch (c) {
+            '(' => try self.addSimpleToken(.LEFT_PAREN),
+            ')' => try self.addSimpleToken(.RIGHT_PAREN),
+            '{' => try self.addSimpleToken(.LEFT_BRACE),
+            '}' => try self.addSimpleToken(.RIGHT_BRACE),
+            ',' => try self.addSimpleToken(.COMMA),
+            '.' => try self.addSimpleToken(.DOT),
+            '-' => try self.addSimpleToken(.MINUS),
+            '+' => try self.addSimpleToken(.PLUS),
+            ';' => try self.addSimpleToken(.SEMICOLON),
+            '*' => try self.addSimpleToken(.STAR),
+            else => {
+                try main.doError(self.line, "Unexpected character");
+            },
+        }
+    }
+
+    pub fn scanTokens(self: *Scanner) !TokenList {
+        // while we aren't at the end, we're still consuming
+        // tokens.
+        while (!self.isAtEnd()) {
+            self.start = self.current;
+            try self.scanToken();
+        }
+
+        try self.addToken(token.Token{
+            .Simple = token.SimpleToken.init(
+                .EOF,
+                "",
+                self.line,
+                {},
+            ),
+        });
+
+        return self.tokens;
+    }
+};
diff --git a/src/token.zig b/src/token.zig
new file mode 100644
index 0000000..0ce1283
--- /dev/null
+++ b/src/token.zig
@@ -0,0 +1,93 @@
+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,
+    FUN,
+    FOR,
+    IF,
+    NIL,
+    OR,
+    PRINT,
+    RETURN,
+    SUPER,
+    THIS,
+    TRUE,
+    VAR,
+    WHILE,
+
+    EOF,
+};
+
+pub fn TokenFactory(
+    comptime T: type,
+) type {
+    return struct {
+        const Self = @This();
+
+        ttype: TokenType,
+        lexeme: []u8,
+        line: usize,
+        literal: T,
+
+        pub fn init(
+            ttype: TokenType,
+            lexeme: []u8,
+            line: usize,
+            literal: T,
+        ) Self {
+            return Self{
+                .ttype = ttype,
+                .lexeme = lexeme,
+                .line = line,
+                .literal = literal,
+            };
+        }
+
+        pub fn printToken(self: Self, stdout: var) !void {
+            try stdout.print(
+                "Token(type={x}, lexeme='{}', line={}\n",
+                self.ttype,
+                self.lexeme,
+                self.line,
+            );
+        }
+    };
+}
+
+pub const SimpleToken = TokenFactory(void);
+
+pub const Token = union {
+    Simple: SimpleToken,
+};