Set the correct render method (boolean or function call)
        and read variables from the current line.

def _compile(self, lines):
        '''Set the correct render method (boolean or function call)
        and read variables from the current line.
        '''
        m = self.__class__.RE_IF.match(lines.current)
        if m is None:
            raise DefineBlockError(
                'Incorrect block definition at line {}, {}\nShould be '
                'something like: #if @foo:'.format(lines.pos, lines.current))
        args = m.group(3)
        self._evaluate = m.group(2).replace('.', '-')
        self._isbool = args is None
        if not self._isbool:
            args = args.strip('() \t')
            self._args = [arg.strip('@ \t').replace('.', '-')
                          for arg in args.split(',')]