serializing to JSON

[mvolkmann]

I'm trying to learn how to use the json_chars predicate defined in this Scryer library: https://github.com/mthom/scryer-prolog/blob/master/src/lib/serialization/json.pl
So far I haven't been able to get it to work.
Can someone share a simple, one-line example?

[triska]

Without knowing anything about the nonterminal, let's ask Prolog for what solutions look like in general:

?- phrase(json_chars(Js), Cs).
   Js = pairs([]), Cs = "{}"
;  Js = pairs([]), Cs = "{} "
;  Js = pairs([]), Cs = "{}  "
;  ... .

OK, not a very fair enumeration, yet a simple, one-line example!

[mvolkmann]

Thanks! Based on this it seems I can specify Prolog data that I wish to turn into JSON using a pairs structure that takes a list. I assume the list should contain pairs of the form key-value. So I tried this:

use_module(library(dcgs)).
use_module(library(serialization/json)).
phrase(json_chars(pairs([foo-alpha, bar-beta])), Cs).

But that doesn't terminate and pressing ctrl-c doesn't stop it. I have to kill it from another terminal window.
I think I am not correctly specifying the data to be converted to JSON.

[triska]

?- phrase(json_chars(pairs([string("alpha")-string("beta")])), Cs).
   Cs = "{\"alpha\":\"beta\"}"
;  Cs = "{\"alpha\":\"beta\"} "
;  Cs = "{\"alpha\":\"beta\"}  "
;  ... .

Alternatively, start with a valid JSON string, and see how json_chars//1 parses it. For example:

?- phrase(json_chars(Js), "{\"alpha\":\"beta\"}").
   Js = pairs([string("alpha")-string("beta")])
;  false.

[mvolkmann]

Thanks so much! I was hoping I could give it any Prolog term and it would serialize it to JSON.
Is it the case that json_chars is not that general purpose?

[trygvis]

@triska So how is one supposed to use json_chars to serialize a structure if it keeps on generating solutions?

Generating variants with extra, insignificant blank space doesn't seem very useful right now :)

@mvolkmann It does seem very low level, dealing only with transforming specific terms into json. You (and I) need something between your terms and the json-oriented terms.