B9 produces not only VM-Images but also text documents such as configuration files required by virtual machines. This module is about creating and merging files containing parsable syntactic structures, such as most configuration files do.

Imagine you would want to create a cloud-init 'user-data' file from a set of 'user-data' snippets which each are valid 'user-data' files in yaml syntax and e.g. a writefiles section. Now the goal is, for b9 to be able to merge these snippets into one, such that all writefiles sections are combined into a single writefile section. Another example is OTP/Erlang sys.config files. This type class is the greatest commonon denominator of types describing a syntax that can be parsed, concatenated e.g. like in the above example and rendered. The actual concatenation operation is the append from Monoid, i.e. like monoid but without the need for an empty element.