Re: lpeg.Carg() weirdness

[Dirk Laurie <dirk.laurie@...>]

2017-06-25 7:51 GMT+02:00 Sean Conner <sean@conman.org>:
> It was thus said that the Great Parke once stated:
>> On Sat, Jun 24, 2017 at 9:22 PM, Sean Conner <sean@conman.org> wrote:
>> >> Why?  What are you trying to do?
>> >
>> >   I have LPeg code to decode JSON data [1].  I received email from a person
>> > about the handling of 'null'---that is, I return a Lua nil value, but this
>> > person wanted a custom value.  I'm not completely swayed by the arguments
>> > for a custom JSON null value, but I would like to provide the option for
>> > such.  I thought a good way to handle a situation would be with Carg()---if
>> > you want a custom null value, one could be provided, but it's optional.
>>
>> Why not use lpeg.Cc(values)?
>
>   Given how I've implemented the module, I return an LPeg userdata, not a
> table (following the other parsing modules [1]).  I'd like to keep that
> format if at all possible (and it's seeming like I can't).  If require()
> passed along any additional paramters to the module, then that could be used
> to pass along a custom JSON null value, but alas, require() doesn't work
> that way.
>
>   So the only way to pass along an alternative null is through additional
> arguments to lpeg.match(), which doesn't work the way I would like.

One very easy method is to use the value of the global variable 'null'.
By default, it is nil, which will give the current behaviour. A user that
needs one can define it himself before invoking the LPeg pattern.

I've made that tiny change to your json.lua, and can report that it works.

-- Dirk