# Buggy code
def tokenize(source, filename=None):
    """Tokenize a Lisp file or string buffer into internal Hy objects.

    Parameters
    ----------
    source: str
        The source to tokenize.
    filename: str, optional
        The filename corresponding to `source`.
    """
    from hy.lex.lexer import lexer
    from hy.lex.parser import parser
    from rply.errors import LexingError

    try:
        return parser.parse(lexer.lex(source), state=ParserState(source, filename))
    except LexingError as e:
        pos = e.getsourcepos()
        raise LexException(
            "Could not identify the next token.",
            filename,
            pos.lineno,
            pos.colno,
            source,
        )


# Traceback (hy.errors.HyCompileError)
Traceback (most recent call last):
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/importer.py", line 180, in hy_eval
_ast, expr = hy_compile(hytree, module_name, get_expr=True)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 2213, in hy_compile
result = compiler.compile(tree)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 460, in compile
ret = self.compile_atom(_type, tree)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 1731, in compile_expression
ret = self.compile_atom(fn, expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 819, in compile_do
return self._compile_branch(expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 545, in _compile_branch
return _branch(self.compile(expr) for expr in exprs)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 318, in _branch
results = list(results)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 545, in <genexpr>
return _branch(self.compile(expr) for expr in exprs)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 460, in compile
ret = self.compile_atom(_type, tree)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 1731, in compile_expression
ret = self.compile_atom(fn, expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 372, in checker
return fn(self, expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 873, in compile_try_expression
name)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 1002, in _compile_catch_expression
body = self._compile_branch(expr)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 545, in _compile_branch
return _branch(self.compile(expr) for expr in exprs)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 318, in _branch
results = list(results)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 545, in <genexpr>
return _branch(self.compile(expr) for expr in exprs)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 460, in compile
ret = self.compile_atom(_type, tree)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 1731, in compile_expression
ret = self.compile_atom(fn, expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 372, in checker
return fn(self, expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 858, in compile_try_expression
body += self.compile(expr.pop(0))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 472, in compile
raise_empty(HyCompileError, e, sys.exc_info()[2])
File "<string>", line 1, in raise_empty
hy.errors.HyCompileError: Internal Compiler Bug 😱
⤷ ImportError: cannot require names: [HySymbol('let')]
Compilation traceback:
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 460, in compile
ret = self.compile_atom(_type, tree)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 1731, in compile_expression
ret = self.compile_atom(fn, expression)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 447, in compile_atom
else _compile_table[atom_type](self, atom))
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/compiler.py", line 1486, in compile_require
require(module, self.module_name, assignments=assignments)
File "/home/johnzhuang/.virtualenvs/hy/lib/python3.6/site-packages/hy/macros.py", line 106, in require
raise ImportError("cannot require names: " + repr(list(unseen)))

# Fixed code
def tokenize(source, filename=None):
    """Tokenize a Lisp file or string buffer into internal Hy objects.

    Parameters
    ----------
    source: str
        The source to tokenize.
    filename: str, optional
        The filename corresponding to `source`.
    """
    from hy.lex.lexer import lexer
    from hy.lex.parser import parser
    from rply.errors import LexingError

    try:
        return parser.parse(lexer.lex(source), state=ParserState(source, filename))
    except LexingError as e:
        pos = e.getsourcepos()
        raise LexException(
            "Could not identify the next token.",
            None,
            filename,
            source,
            max(pos.lineno, 1),
            max(pos.colno, 1),
        )
    except LexException as e:
        raise e