{% macro redact(topSecret) %}
{% set length = topSecret|length - 4 %}
{{ topSecret|slice(0, 3) }}{% for i in 0..length %}*{% endfor %}
{% endmacro %}
{# You have to import from _self if the macro is declared in the same file. #}
{% import _self as sharpie %}
{{ sharpie.redact('Top secret information') }}
{# => Top******************* #}