1:- encoding(utf8).
    2/*  Part of SWI-Prolog
    3
    4    Author:        Torbjörn Lager and Jan Wielemaker
    5    E-mail:        J.Wielemaker@vu.nl
    6    WWW:           http://www.swi-prolog.org
    7    Copyright (c)  2014-2015, Torbjörn Lager,
    8                              VU University Amsterdam
    9    All rights reserved.
   10
   11    Redistribution and use in source and binary forms, with or without
   12    modification, are permitted provided that the following conditions
   13    are met:
   14
   15    1. Redistributions of source code must retain the above copyright
   16       notice, this list of conditions and the following disclaimer.
   17
   18    2. Redistributions in binary form must reproduce the above copyright
   19       notice, this list of conditions and the following disclaimer in
   20       the documentation and/or other materials provided with the
   21       distribution.
   22
   23    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   24    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   25    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   26    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   27    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   28    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   29    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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   31    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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   35*/
   36
   37:- module(term_to_json,
   38          [ term_to_json/3,                     % +Term, +Bindings, -Json
   39            term_to_json/2                      % +Term, -Json
   40          ]).   41:- use_module(library(apply)).   42:- use_module(library(error)).

 term_to_json(+Term, +Bindings, -JsonTerm) is det

 term_to_json(+Term, -JsonTerm) is det

Convert any general Prolog term into a JSON term. Prolog lists are treated in a special way. Also, JSON terms are not converted. Mapping:

• Variable: {"type":"var", "name":<string>}
• Atom: {"type":"atom", "value":<string>}
• Integer: {"type":"integer", "value":<integer>}
• Float: {"type":"float", "value":<float>}
• List: JSON array
• Dict: a JSON object. Values are processed recursively. (the tag is ignored)
• json([Key=Value, ...]): a JSON object Values are processed recursively.
• compound: {"type":"compound", "functor":<string>, "args":<array>}

Arguments:

Bindings

- is a list of Name=Var terms for variables that get their name from the environment.

   65term_to_json(Term, JSON) :-
   66    term_to_json(Term, [], JSON).
   67term_to_json(Term, Bindings, JSON) :-
   68    findall(X,
   69            (   maplist(bind_var, Bindings),
   70                numbervars(Term, 0, _, [singletons(true)]),
   71                to_json(Term, X)
   72            ),
   73            [JSON]).
   74
   75bind_var(Name=Var) :-
   76    (   var(Var)
   77    ->  Var = '$VAR'(Name)
   78    ;   true
   79    ).
   80
   81to_json(Term, '_') :-
   82    var(Term),
   83    !.
   84to_json(@(Symbol), Symbol) :-                   % compatibility
   85    atom(Symbol),
   86    json_symbol(Symbol),
   87    !.
   88to_json(Term, Term) :-
   89    atom(Term),
   90    !.                          % interpreted as a string
   91to_json(Term, Term) :-
   92    string(Term),
   93    !.
   94to_json(Term, Value) :-
   95    integer(Term),
   96    !,
   97    (   Term >= -(2**31), Term < 2**31
   98    ->  Value = Term
   99    ;   atom_number(Value, Term)
  100    ).
  101to_json(Term, Term) :-
  102    float(Term),
  103    !.
  104to_json(Term, JsonList) :-
  105    is_list(Term),
  106    !,
  107    maplist(to_json, Term, JsonList).
  108to_json(json(Pairs0), Term) :-
  109    must_be(list, Pairs0),
  110    maplist(pair_value_to_json_ex, Pairs0, Pairs),
  111    dict_pairs(Term, json, Pairs).
  112to_json(Term0, Term) :-
  113    is_dict(Term0),
  114    !,
  115    dict_pairs(Term0, Tag, Pairs0),
  116    maplist(pair_value_to_json, Pairs0, Pairs),
  117    dict_pairs(Term, Tag, Pairs).
  118to_json('$VAR'(Name), VarName) :-
  119    !,
  120    format(string(VarName), '~W', ['$VAR'(Name), [numbervars(true)]]).
  121to_json(Term, json{functor:F, args:JsonArgs}) :-
  122    Term =.. [F|Args],
  123    maplist(to_json, Args, JsonArgs).
  124
  125json_symbol(null).
  126json_symbol(true).
  127json_symbol(false).
  128
  129pair_value_to_json(Key-Value0, Key-Value) :-
  130    to_json(Value0, Value).
  131
  132pair_value_to_json_ex(Key=Value0, Key-Value) :-
  133    (atom(Key) ; integer(Key)),
  134    !,
  135    to_json(Value0, Value).
  136pair_value_to_json_ex(Elem, _) :-
  137    domain_error(json_key_value, Elem)