{% macro category_listing(page, language, base_url, none_description) -%}
	{%- if page.meta.category is defined -%}
		{%- for c in page.meta.category -%}
			{%- if not loop.first %}, {% endif %}<a href="{{ base_url }}{{ c }}/">{{ c }}</a>

			{%- set cat_names = site.groups["category_name"].pages
				| filter(attribute="meta.language", value=language)
				| map(attribute="meta.category_name") -%}
			{# what's up with this? Inlining the above into the condition is a
			syntax error. Filters apparently cannot appear in expressions,
			although they are valid inside "{{ }}". #}
			{%- if not cat_names is containing(c) -%}
				{{ throw(message="category `" ~ c ~ "' appears to be missing its page") }}
			{%- endif -%}
		{%- endfor -%}
	{%- else -%}
		{{ none_description }}
	{%- endif -%}
{%- endmacro category_listing %}