I think it’s just normal Lua code.

Here’s a quick json converter (based on https://stackoverflow.com/a/55575074), assuming you have lua installed:

local function to_json(obj)
    local result = {}
    for key, value in pairs(obj) do
        if type(value) == "string" then
            value = string.format("\"%s\"", value)
        elseif type(value) == "table" then
            value = to_json(value)
        end
        table.insert(result, string.format("\"%s\":%s", key, value))
    end
    return "{" .. table.concat(result, ",") .. "}"
end

function item(obj)
    print(to_json(obj))
end

dofile(arg[1])

It just defines the item function to print json, and executes the data file.

arg[1], the first command line argument, is the path to the data file:

$  lua to_json.lua path/to/datafile.list

and pipe the output to something.json or whatever else you want to do.