conditional Chatbot response

Hi ! I'm trying to work with your Chatbot and I was wondering if there is a posibility to only make the Bot answering under a certain condition. I tried it with following template but it didn't work:

{% block %}
{% client %}(?P.*){% endclient %}
{% if {% call Myfuncion:%query%} %}
{% response %}My answer.{% endresponse %}
{% endif %}
{% endblock %}

The funcion Myfuncion returns True / False depending on the client's query.
Thank you in advance for your help!