def prepare_predicate(next, token):
    # FIXME: replace with real parser!!! refs:
    # http://effbot.org/zone/simple-iterator-parser.htm
    # http://javascript.crockford.com/tdop/tdop.html
    signature = ''
    predicate = []
    while 1:
        token = next()
        if token[0] == "]":
            break
        if token == ('', ''):
            # ignore whitespace
            continue
        if token[0] and token[0][:1] in "'\"":
            token = "'", token[0][1:-1]
        signature += token[0] or "-"
        predicate.append(token[1])

    # use signature to determine predicate type
    if signature == "@-":
        # [@attribute] predicate
        key = predicate[1]
        def select(result):
            for elem in result:
                if elem.get(key) is not None:
                    yield elem
        return select
    if signature == "@-='":
        # [@attribute='value']
        key = predicate[1]
        value = predicate[-1]
        def select(result):
            for elem in result:
                if elem.get(key) == value:
                    yield elem
        return select
    if signature == "-" and not re.match(r"-?\d+$", predicate[0]):
        # [tag]
        tag = predicate[0]
        def select(result):
            for elem in result:
                for _ in elem.iterchildren(tag):
                    yield elem
                    break
        return select
    if signature == ".='" or (signature == "-='" and not re.match(r"-?\d+$", predicate[0])):
        # [.='value'] or [tag='value']
        tag = predicate[0]
        value = predicate[-1]
        if tag:
            def select(result):
                for elem in result:
                    for e in elem.iterchildren(tag):
                        if "".join(e.itertext()) == value:
                            yield elem
                            break
        else:
            def select(result):
                for elem in result:
                    if "".join(elem.itertext()) == value:
                        yield elem
        return select
    if signature == "-" or signature == "-()" or signature == "-()-":
        # [index] or [last()] or [last()-index]
        if signature == "-":
            # [index]
            index = int(predicate[0]) - 1
            if index < 0:
                if index == -1:
                    raise SyntaxError(
                        "indices in path predicates are 1-based, not 0-based")
                else:
                    raise SyntaxError("path index >= 1 expected")
        else:
            if predicate[0] != "last":
                raise SyntaxError("unsupported function")
            if signature == "-()-":
                try:
                    index = int(predicate[2]) - 1
                except ValueError:
                    raise SyntaxError("unsupported expression")
            else:
                index = -1
        def select(result):
            for elem in result:
                parent = elem.getparent()
                if parent is None:
                    continue
                try:
                    # FIXME: what if the selector is "*" ?
                    elems = list(parent.iterchildren(elem.tag))
                    if elems[index] is elem:
                        yield elem
                except IndexError:
                    pass
        return select
    raise SyntaxError("invalid predicate")