Re: Lua as a configuration language -- validation

[Chris Smith <space.dandy@...>]

> On 22 Aug 2019, at 13:58, Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br> wrote:
> 
> Please show us a sample configuration file and what validation you have in mind.


Ok, well let’s take a trivial and contrived example of a UI configuration.  The configuration might look something like this:

UI = {
  mainwindow = {
    size = {
      width = 100,
      height = 200
    }
  }
}

Now, my code wants to use this information very simply:

local width = config.UI.mainwindow.size.width

But before I can do that, as a minimum I need to verify the structure and format of the config before I can safely use it.  Very naively, I might do something like this:

local width
if type(UI) == ’table’ then
  if type(UI.mainwindow) == ’table’ then
    if type(UI.mainwindow.size) == ’table’ then
      — now can access safely
      width = UI.mainwindow.size.width
    end
  end
end

If type(width) == ’number’ then
  — do something
end

That’s an awful lot of cruft just for one element, and I haven’t even dealt with range checking, default values and passing back warnings to the user.  There are a few ways I can think to make it simpler, like wrapping a simple access in a pcall to see if it crashes or not, but this must be quite a common issue and I wondered if there are already some standard libraries or patterns to deal with it before I start re-inventing wheels.

Regards,
Chris
—
Chris Smith <space.dandy@icloud.com>