Generating Specials

Generating the list of specials

We’ll start with the list of specials since it’s conceptually simpler and a prerequisite of other generators. The method here is to first extract the list of all item names from the price list, and then create a matching table of specials. Let’s take a look at how it can be done.

defp special_list(price_list) do
  items = for {name, _} <- price_list, do: name

  let specials <- list({elements(items), choose(2, 5), integer()}) do
    sorted = Enum.sort(specials)
    Enum.dedup_by(sorted, fn {x, _, _} -> x end)
  end
end

The generated list of specials contains the name of the item, how many of them are required for the special to apply, and then the price for the whole group. The specials are generated from randomly selected entries from the item list with the duplicates removed, so that there is always a matching non-special item to any special one. Note that the special price can be higher than the non-special price with this generator.

Generating the list of regular items

It is a bit tricky to generate the list of items that are never special. We’ll call them regular items. We have to make it so we generate zero or more items, as long as the maximal value is below any special discount values for the item. Let’s take a look at how it can be done.