function get_patterns(...)
    local params            = {...}
    local occurrences       = type(params[5]) == "table" and params[4] or {}

    -- get_patterns(str[, min_length = 1[, max_length = 1]])
    local str               = type(params[1]) == "string" and params[1] or error("String expected, got ".. type(params[1]))
    local min_length        = type(params[2]) == "number" and params[2] or 1
    local max_length        = type(params[3]) == "number" and params[3] or min_length

    for len = min_length, max_length do
        for init = 1, #str - len do
            local tmp = string.sub(str, init, init + len - 1)
            occurrences[tmp] = occurrences[tmp] and ( occurrences[tmp] + 1 ) or 1
        end
    end
    return occurrences
end