From Rosetta Code
This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.

Wren-perm is a module which enables the permutations and combinations of a given array to be counted or emitted using the Wren programming language. It consists of three classes: Perm, Comb and Powerset all of whose methods are static.

It is the thirty-fourth in a series of modules (listed on the language's main page) designed to assist with writing Rosetta Code tasks so the same code does not have to be written or copy/pasted time and time again thereby bloating a task's script code unnecessarily.

To use it you need to copy the source code (in the talk page) to a text file called perm.wren and place this in the same directory as the importing script so the command line interpreter or host application can find it.

As there is a dependency on the Wren-check module, you also need to copy that (if it is not already present) to the same directory as described here. If you need to use the Check class directly, that can even be imported via Wren-perm itself.