Issues with JSON utilities

[astoff]

I have encountered some issues with the json routines. The following lua file

kpse.set_program_name("luatex")
require "lualibs"

inspect("array", utilities.json.tojson({[1] = 0}))
inspect("object", utilities.json.tojson({a = 0}))

generates

array
[
 0
]
object
{
 "a" : "0"
}

The object should be {"a": 0} here.

Second, the script

kpse.set_program_name("luatex")
require "lualibs"
utilities.json.tojson(0)

crashes with the following message:

...exmf-dist/tex/luatex/lualibs/lualibs-extended-merged.lua:3076: bad argument #1 to 'lpegmatch' (lpeg-pattern expected, got nil)

Finally, it would be important for the JSON encoder to be able to produce null values when needed (and perhaps for the decoder not to translate JSON nulls into Lua nils, at least if requested by the user). This could be done by checking for a special value utilities.json.null.

Lastly, it would be nice to be able to generate compact JSONs without additional blank spaces.