diff --git a/chapter2.py b/chapter2.py
index f520994..2e8f89a 100644
--- a/chapter2.py
+++ b/chapter2.py
@@ -1,4 +1,4 @@
-# Chapter 1 - Lexer
+# Chapter 1&2 - Lexer and Parser
 
 from collections import namedtuple
 from enum import Enum
diff --git a/chapter3.py b/chapter3.py
new file mode 100644
index 0000000..307ecca
--- /dev/null
+++ b/chapter3.py
@@ -0,0 +1,405 @@
+# Chapter 3 - Code generation to LLVM IR
+
+from collections import namedtuple
+from enum import Enum
+
+import llvmlite.ir as ir
+
+# Each token is a tuple of kind and value. kind is one of the enumeration values
+# in TokenKind. value is the textual value of the token in the input.
+class TokenKind(Enum):
+    EOF = -1
+    DEF = -2
+    EXTERN = -3
+    IDENTIFIER = -4
+    NUMBER = -5
+    OPERATOR = -6
+
+
+Token = namedtuple('Token', 'kind value')
+
+
+class Lexer(object):
+    """Lexer for Kaleidoscope.
+
+    Initialize the lexer with a string buffer. tokens() returns a generator that
+    can be queried for tokens. The generator will emit an EOF token before
+    stopping.
+    """
+    def __init__(self, buf):
+        assert len(buf) >= 1
+        self.buf = buf
+        self.pos = 0
+        self.lastchar = self.buf[0]
+
+    def tokens(self):
+        while self.lastchar:
+            # Skip whitespace
+            while self.lastchar.isspace():
+                self._advance()
+            # Identifier or keyword
+            if self.lastchar.isalpha():
+                id_str = ''
+                while self.lastchar.isalnum():
+                    id_str += self.lastchar
+                    self._advance()
+                if id_str == 'def':
+                    yield Token(kind=TokenKind.DEF, value=id_str)
+                elif id_str == 'extern':
+                    yield Token(kind=TokenKind.EXTERN, value=id_str)
+                else:
+                    yield Token(kind=TokenKind.IDENTIFIER, value=id_str)
+            # Number
+            elif self.lastchar.isdigit() or self.lastchar == '.':
+                num_str = ''
+                while self.lastchar.isdigit() or self.lastchar == '.':
+                    num_str += self.lastchar
+                    self._advance()
+                yield Token(kind=TokenKind.NUMBER, value=num_str)
+            # Comment
+            elif self.lastchar == '#':
+                self._advance()
+                while self.lastchar and self.lastchar not in '\r\n':
+                    self._advance()
+            elif self.lastchar:
+                # Some other char
+                yield Token(kind=TokenKind.OPERATOR, value=self.lastchar)
+                self._advance()
+        yield Token(kind=TokenKind.EOF, value='')
+
+    def _advance(self):
+        try:
+            self.pos += 1
+            self.lastchar = self.buf[self.pos]
+        except IndexError:
+            self.lastchar = ''
+
+
+# AST hierarchy
+class ASTNode(object):
+    def dump(self, indent=0):
+        raise NotImplementedError
+
+
+class ExprAST(ASTNode):
+    pass
+
+
+class NumberExprAST(ExprAST):
+    def __init__(self, val):
+        self.val = val
+
+    def dump(self, indent=0):
+        return '{0}{1}[{2}]'.format(
+            ' ' * indent, self.__class__.__name__, self.val)
+
+
+class VariableExprAST(ExprAST):
+    def __init__(self, name):
+        self.name = name
+
+    def dump(self, indent=0):
+        return '{0}{1}[{2}]'.format(
+            ' ' * indent, self.__class__.__name__, self.name)
+
+
+class BinaryExprAST(ExprAST):
+    def __init__(self, op, lhs, rhs):
+        self.op = op
+        self.lhs = lhs
+        self.rhs = rhs
+
+    def dump(self, indent=0):
+        s = '{0}{1}[{2}]\n'.format(
+            ' ' * indent, self.__class__.__name__, self.op)
+        s += self.lhs.dump(indent + 2) + '\n'
+        s += self.rhs.dump(indent + 2)
+        return s
+
+
+class CallExprAST(ExprAST):
+    def __init__(self, callee, args):
+        self.callee = callee
+        self.args = args
+
+    def dump(self, indent=0):
+        s = '{0}{1}[{2}]\n'.format(
+            ' ' * indent, self.__class__.__name__, self.callee)
+        for arg in self.args:
+            s += arg.dump(indent + 2) + '\n'
+        return s[:-1]  # snip out trailing '\n'
+
+
+class PrototypeAST(ASTNode):
+    def __init__(self, name, argnames):
+        self.name = name
+        self.argnames = argnames
+
+    def dump(self, indent=0):
+        return '{0}{1}[{2}]'.format(
+            ' ' * indent, self.__class__.__name__, ', '.join(self.argnames))
+
+
+class FunctionAST(ASTNode):
+    def __init__(self, proto, body):
+        self.proto = proto
+        self.body = body
+
+    def dump(self, indent=0):
+        s = '{0}{1}[{2}]\n'.format(
+            ' ' * indent, self.__class__.__name__, self.proto.dump())
+        s += self.body.dump(indent + 2) + '\n'
+        return s
+
+
+class ParseError(Exception): pass
+
+
+class Parser(object):
+    def __init__(self, buf):
+        self.token_generator = Lexer(buf).tokens()
+        self.cur_tok = None
+        self._get_next_token()
+
+    # toplevel ::= definition | external | expression | ';'
+    def parse_toplevel(self):
+        if self.cur_tok.kind == TokenKind.EXTERN:
+            return self._parse_external()
+        elif self.cur_tok.kind == TokenKind.DEF:
+            return self._parse_definition()
+        elif self._cur_tok_is_operator(';'):
+            self._get_next_token()
+            return None
+        else:
+            return self._parse_toplevel_expression()
+
+    def _get_next_token(self):
+        self.cur_tok = next(self.token_generator)
+
+    _precedence_map = {'<': 10, '+': 20, '-': 20, '*': 40}
+
+    def _cur_tok_precedence(self):
+        """Get the operator precedence of the current token."""
+        try:
+            return Parser._precedence_map[self.cur_tok.value]
+        except KeyError:
+            return -1
+
+    def _cur_tok_is_operator(self, op):
+        """Query whether the current token is the operator op"""
+        return (self.cur_tok.kind == TokenKind.OPERATOR and
+                self.cur_tok.value == op)
+
+    # identifierexpr
+    #   ::= identifier
+    #   ::= identifier '(' expression* ')'
+    def _parse_identifier_expr(self):
+        id_name = self.cur_tok.value
+        self._get_next_token()
+        # If followed by a '(' it's a call; otherwise, a simple variable ref.
+        if not self._cur_tok_is_operator('('):
+            return VariableExprAST(id_name)
+
+        self._get_next_token()
+        args = []
+        if not self._cur_tok_is_operator(')'):
+            while True:
+                args.append(self._parse_expression())
+                if self._cur_tok_is_operator(')'):
+                    break
+                if not self._cur_tok_is_operator(','):
+                    raise ParseError('Expected ")" or "," in argument list')
+                self._get_next_token()
+
+        self._get_next_token()  # consume the ')'
+        return CallExprAST(id_name, args)
+
+    # numberexpr ::= number
+    def _parse_number_expr(self):
+        result = NumberExprAST(self.cur_tok.value)
+        self._get_next_token()  # consume the number
+        return result
+
+    # parenexpr ::= '(' expression ')'
+    def _parse_paren_expr(self):
+        self._get_next_token()  # consume the '('
+        expr = self._parse_expression()
+        if not self._cur_tok_is_operator(')'):
+            raise ParseError('Expected ")"')
+        self._get_next_token()  # consume the ')'
+        return expr
+
+    # primary
+    #   ::= identifierexpr
+    #   ::= numberexpr
+    #   ::= parenexpr
+    def _parse_primary(self):
+        if self.cur_tok.kind == TokenKind.IDENTIFIER:
+            return self._parse_identifier_expr()
+        elif self.cur_tok.kind == TokenKind.NUMBER:
+            return self._parse_number_expr()
+        elif self._cur_tok_is_operator('('):
+            return self._parse_paren_expr()
+        else:
+            raise ParseError('Unknown token when expecting an expression')
+
+    # binoprhs ::= (<binop> primary)*
+    def _parse_binop_rhs(self, expr_prec, lhs):
+        """Parse the right-hand-side of a binary expression.
+
+        expr_prec: minimal precedence to keep going (precedence climbing).
+        lhs: AST of the left-hand-side.
+        """
+        while True:
+            cur_prec = self._cur_tok_precedence()
+            # If this is a binary operator with precedence lower than the
+            # currently parsed sub-expression, bail out. If it binds at least
+            # as tightly, keep going.
+            # Note that the precedence of non-operators is defined to be -1,
+            # so this condition handles cases when the expression ended.
+            if cur_prec < expr_prec:
+                return lhs
+            op = self.cur_tok.value
+            self._get_next_token()  # consume the operator
+            rhs = self._parse_primary()
+
+            next_prec = self._cur_tok_precedence()
+            # There are three options:
+            # 1. next_prec > cur_prec: we need to make a recursive call
+            # 2. next_prec == cur_prec: no need for a recursive call, the next
+            #    iteration of this loop will handle it.
+            # 3. next_prec < cur_prec: no need for a recursive call, combine
+            #    lhs and the next iteration will immediately bail out.
+            if cur_prec < next_prec:
+                rhs = self._parse_binop_rhs(cur_prec + 1, rhs)
+
+            # Merge lhs/rhs
+            lhs = BinaryExprAST(op, lhs, rhs)
+
+    # expression ::= primary binoprhs
+    def _parse_expression(self):
+        lhs = self._parse_primary()
+        # Start with precedence 0 because we want to bind any operator to the
+        # expression at this point.
+        return self._parse_binop_rhs(0, lhs)
+
+    # prototype ::= id '(' id* ')'
+    def _parse_prototype(self):
+        if self.cur_tok.kind != TokenKind.IDENTIFIER:
+            raise ParseError('Expected function name in prototype')
+        name = self.cur_tok.value
+        self._get_next_token()  # consume the name
+        if not self._cur_tok_is_operator('('):
+            raise ParseError('Expected "(" in prototype')
+        self._get_next_token()  # consume '('
+        argnames = []
+        while self.cur_tok.kind == TokenKind.IDENTIFIER:
+            argnames.append(self.cur_tok.value)
+            self._get_next_token()
+        if not self._cur_tok_is_operator(')'):
+            raise ParseError('Expected ")" in prototype')
+        self._get_next_token()  # consume ')'
+        return PrototypeAST(name, argnames)
+
+    # external ::= 'extern' prototype
+    def _parse_external(self):
+        self._get_next_token()  # consume 'extern'
+        return self._parse_prototype()
+
+    # definition ::= 'def' prototype expression
+    def _parse_definition(self):
+        self._get_next_token()  # consume 'def'
+        proto = self._parse_prototype()
+        expr = self._parse_expression()
+        return FunctionAST(proto, expr)
+
+    # toplevel ::= expression
+    def _parse_toplevel_expression(self):
+        expr = self._parse_expression()
+        # Anonymous function
+        return FunctionAST(PrototypeAST('', []), expr)
+
+
+class CodegenError(Exception): pass
+
+
+class LLVMCodeGenerator(object):
+    def __init__(self):
+        """Initialize the code generator.
+
+        This creates a new LLVM module into which code is generated. The
+        generate_code() method can be called multiple times. It adds the code
+        generated for this node into the module, and returns the module.
+        """
+        self.module = ir.Module()
+
+        # Current IR builder.
+        self.builder = None
+
+        # Manages a symbol table while a function is being codegen'd. Maps var
+        # names to ir.Value.
+        self.func_symtab = {}
+
+    def generate_code(self, node):
+        assert isinstance(node, (PrototypeAST, FunctionAST))
+        self._codegen(node)
+        return self.module
+
+    def _codegen(self, node):
+        """Node visitor. Dispathces upon node type.
+
+        For AST node of class Foo, calls self._codegen_Foo. Each visitor is
+        expected to return a llvmlite.ir.Value.
+        """
+        method = 'visit_' + node.__class__.__name__
+        return getattr(self, method)(node)
+
+    def _codegen_NumberExprAST(self, node):
+        return self.builder.constant(ir.DoubleType(), float(node.val))
+
+    def _codegen_VariableExprAST(self, node):
+        return self.symtab[node.name]
+
+    def _codegen_PrototypeAST(self, node):
+        # Create a function type
+        func_ty = ir.FunctionType(ir.DoubleType(),
+                                  [ir.DoubleType() * len(node.argnames)])
+
+        # If a function with this name already exists in the module...
+        if node.name in self.module.globals:
+            # We only allow the case in which a declaration exists and now the
+            # function is defined (or redeclared) with the same number of args.
+            existing_func = self.module[node.name]
+            if not isinstance(existing_func, ir.Function):
+                raise CodegenError('Function/Global name collision', node.name)
+            if not existing_func.is_declaration():
+                raise CodegenError('Redifinition of {0}'.format(node.name))
+            if len(existing_func.function_type.args) != len(func_ty.args):
+                raise CodegenError(
+                    'Redifinition with different number of arguments')
+            func = self.module.globals[node.name]
+        else:
+            # Otherwise create a new function
+            func = ir.Function(self.module, func_ty, node.name)
+        # Set function argument names from AST
+        for i in range(len(func.args)):
+            func.args[i].name = node.argnames[i]
+        return func
+
+    def _codegen_FunctionAST(self, node):
+        # Create the function skeleton from the prototype.
+        func = self._codegen(node.proto)
+        # Create the entry BB in the function and set the builder to it.
+        bb_entry = func.append_basic_block('entry')
+        self.builder = ir.IRBuilder(bb_entry)
+
+        # We're going to generate the function body now. Reset the symbol table.
+        self.func_symtab = {}
+        retval = self._codegen(node.body)
+        irbuilder.ret(retval)
+        return func
+
+
+if __name__ == '__main__':
+    pass
+