Re: json_to_prolog help

Hello,

On Mon, Jul 29, 2013 at 3:46 PM, Daniel Elliott
<[email protected]> wrote:
> Wouter, thank you for your response.  It turns out that upgrade to 6.4
> was all that I needed to make this work -- I do not need to include
> the type information in the json_object specification (it works with
> or without).  My guess is that using the type thing is necessary only
> when the json_object specifications are insufficient to be unique.  Is
> that your understanding?
>
> Everyone, I have a follow-up question.  Now that I have my lovely
> reading from the json_to_prolog predicate, how do I use it?  Here is
> my example:
>
> ?-json_to_prolog(json([passwd='1234',datetime='41234',data=json([sensor_id=1,data=[json([raw=2,eng=3.3])]),json([sensor_id=2,data=json([raw=3,eng=4.3])])]]),PRLG_Obj).
> PRLG_Obj = reading('1234', '41234', [reading_datum(1, datum(2, 3.3)),
> reading_datum(2, datum(3, 4.3))], []).
>
> I've tried using the access method laid out in the library(record)
> documentation:
>
> ?- json_to_prolog(json([passwd='1234',datetime='41234',data=[json([sensor_id=1,data=json([raw=2,eng=3.3])]),json([sensor_id=2,data=json([raw=3,eng=4.3])])]]),PRLG_Obj),
> reading_pass\
> wd(PRLG_Obj,X).
> ERROR: toplevel: Undefined procedure: reading_passwd/2 (DWIM could not
> correct goal)
>
> What, other than "reading_passwd(PRLG_Obj,X)" should I use to access
> the data in the data structure returned by json_to_prolog.
>
> Sorry for the bad formatting, the browser is wrecking havoc on the
> code listing.  Thank you for your time.
>
> - dan
>
>
> On Mon, Jul 29, 2013 at 12:37 PM, Wouter Beek <[email protected]> wrote:
>> Hi Daniel,
>>
>> Nice to hear that you're using SWI-Prolog for a production system!
>>
>> I've been playing around with the JSON format in SWI-Prolog myself recently.
>> The problem is that JSON does not give the type of an object. Luckily, the
>> json_object directive accounts for that, since it allows you to add a type.
>>
>> For your code fragments, this would look as follows:
>> ~~~{.pl}
>> :- json_object datum(raw:integer, eng:float) + [type=datum].
>> :- json_object reading_error(sensor_id:integer, rply_code:integer) +
>> [type=reading_error].
>> :- json_object reading_datum(sensor_id:integer, data:datum/2) +
>> [type=reading_datum].
>> :- json_object reading(passwd:integer, datetime:integer,
>> data:list(reading_datum/2)) + [type=reading].
>> ~~~
>>
>> Now when you do
>> `prolog_to_json(reading(1234,41234,[reading_datum(1,datum(2,3.3))]), JSON)`
>> you get:
>> ~~~{.pl}
>> JSON =
>> json([passwd=1234,datetime=41234,data=[json([sensor_id=1,data=json([raw=2,eng=3.3,type=datum]),type=reading_datum])],type=reading])
>> ~~~
>> Notice the types in there!
>>
>> When you do `json_to_prolog(JSON,PL)` on this result, you get:
>> ~~~{.pl}
>> PL = reading(1234,41234,[reading_datum(1,datum(2,3.3))])
>> ~~~
>> The result that you were after (I hope :-)).
>>
>> PS: Updating to a version >= 6.3.19 could be beneficial for you, since JSON
>> support received several updates in that release. Here's the relevant
>> improvements from the changelog:
>> ~~~{.txt}
>> * FIXED: Disambiguating JSON->Prolog translation.
>> * MODIFIED: Make json_to_prolog/2 ignore fields in the json that are
>>   not specified in the json_object/1 declaration.  If multiple rules
>>   now apply, the one producing the Prolog term with the highest arity
>>   is selected.
>> * ADDED: library(http/json_convert) - disjunction of types using
>>   (TypeA|TypeB) - null `type' to demand the key is not present -
>>   Handle specified defaults as optional fields in the JSON input.
>> * FIXED: library(http/json_convert): properly handle types such as
>>   list(atom).
>> ~~~
>>
>> ---
>> Cheers!,
>> Wouter.
>>
>> E-mail: [email protected]
>> WWW: www.wouterbeek.com
>> Tel.: 0647674624
>>
>>
>> On Mon, Jul 29, 2013 at 6:46 PM, Daniel Elliott <[email protected]>
>> wrote:
>>>
>>> Hello,
>>>
>>> I am having some difficulties with the following MWE.  I'm new to
>>> Prolog and this is a small part of a prototype which will, hopefully,
>>> make Prolog a significant part of our production system!  I am
>>> uncertain if my approach is fundamentally flawed (not using the
>>> library correctly), if there is a error, or if I am running up on a
>>> limitation of the JSON support.  I am using pl-6.2.6 which I
>>> downloaded and built.
>>>
>>> Here, I am working on code to parse JSON.  The problem is that, in my
>>> example, it does not return a reading record but a json record (may
>>> not be the proper terminology).
>>>
>>> :- use_module(library(http/json)).
>>> :- use_module(library(http/json_convert)).
>>> :- json_object
>>> datum(raw:integer, eng:float).
>>> :- json_object
>>> reading_error(sensor_id:integer, rply_code:integer).
>>> :- json_object
>>> reading_datum(sensor_id:integer, data:datum/2).
>>> :- json_object
>>> reading(passwd:integer, datetime:integer, data:list(reading_datum/2)).
>>>
>>> Here is the result of two illustrative queries:
>>>
>>> ?-
>>> prolog_to_json(reading(1234,41234,[reading_datum(1,datum(2,3.3))]),JSON_Obj),
>>> format(user_output, '~w', JSON_Obj).
>>>
>>> json([passwd=1234,datetime=41234,data=[json([sensor_id=1,data=json([raw=2,eng=3.3])])]])
>>>
>>> ?-
>>> json_to_prolog(json([passwd=1234,datetime=41234,data=[json([sensor_id=1,data=json([raw=2,eng=3.3])])]]),PRLG_Obj).
>>> PRLG_Obj = json([passwd=1234, datetime=41234, data=[reading_datum(1,
>>> datum(2, 3.3))]]).
>>>
>>> I want PRLG_Obj to be reading(...), not json(....).
>>>
>>> Any help over this hump would be greatly appreciated.  Thank you in
>>> advance.
>>>
>>> - dan elliott
>>> _______________________________________________
>>> SWI-Prolog mailing list
>>> [email protected]
>>> https://lists.iai.uni-bonn.de/mailman/listinfo.cgi/swi-prolog
>>>
>>

I see that I have to do something like this:

?- json_to_prolog(json([passwd='1234',datetime='41234',data=[json([sensor_id=1,data=json([raw=2,eng=3.3])]),json([sensor_id=2,data=json([raw=3,eng=4.3])])]]),PRLG_Obj),
PRLG_Obj = r\
eading(P,D,Dd,Ed).
PRLG_Obj = reading('1234', '41234', [reading_datum(1, datum(2, 3.3)),
reading_datum(2, datum(3, 4.3))], []),
P = '1234',
D = '41234',
Dd = [reading_datum(1, datum(2, 3.3)), reading_datum(2, datum(3,
4.3))],
Ed = [].

I guess I need to learn more about this "PRLG_Obj = ..." notation.
Feel free to throw about any pointers.

Thank you.

- dan elliott