/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2007-2014, University of Amsterdam
VU University Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
:- module(json_convert,
[ prolog_to_json/2, % :Term, -JSON object
json_to_prolog/2, % +JSON, :Term
(json_object)/1, % +Definition
op(1150, fx, (json_object))
]).
:- use_module(library(error)).
:- use_module(library(pairs)).
:- use_module(library(apply)).
:- use_module(json).
:- meta_predicate
prolog_to_json(:, -),
json_to_prolog(+, :).
:- public
clear_cache/0,
prolog_list_to_json/3, % +ListIn, -ListOut, +Module
prolog_to_json/3, % +In, -Out, +Module
prolog_bool_to_json/2. % +In, -Boolean
/** <module> Convert between JSON terms and Prolog application terms
The idea behind this module is to provide a flexible high-level mapping
between Prolog terms as you would like to see them in your application
and the standard representation of a JSON object as a Prolog term. For
example, an X-Y point may be represented in JSON as =|{"x":25,
"y":50}|=. Represented in Prolog this becomes json([x=25,y=50]), but
this is a pretty non-natural representation from the Prolog point of
view.
This module allows for defining records (just like library(record)) that
provide transparent two-way transformation between the two
representations.
==
:- json_object
point(x:integer, y:integer).
==
This declaration causes prolog_to_json/2 to translate the native Prolog
representation into a JSON Term:
==
?- prolog_to_json(point(25,50), X).
X = json([x=25, y=50])
==
A json_object/1 declaration can define multiple objects separated by a
comma (,), similar to the dynamic/1 directive. Optionally, a declaration
can be qualified using a module. The conversion predicates
prolog_to_json/2 and json_to_prolog/2 first try a conversion associated
with the calling module. If not successful, they try conversions
associated with the module =user=.
JSON objects have no _type_. This can be solved by adding an extra field
to the JSON object, e.g. =|{"type":"point", "x":25, "y":50}|=. As Prolog
records are typed by their functor we need some notation to handle this
gracefully. This is achieved by adding +Fields to the declaration. I.e.
==
:- json_object
point(x:integer, y:integer) + [type=point].
==
Using this declaration, the conversion becomes:
==
?- prolog_to_json(point(25,50), X).
X = json([x=25, y=50, type=point])
==
The predicate json_to_prolog/2 is often used after http_read_json/2 and
prolog_to_json/2 before reply_json/1. For now we consider them seperate
predicates because the transformation may be too general, too slow or
not needed for dedicated applications. Using a seperate step also
simplifies debugging this rather complicated process.
@tbd Ignore extra fields. Using a partial list of _extra_?
@tbd Consider a sensible default for handling JSON =null=. Conversion
to Prolog could translate @null into a variable if the desired type
is not =any=. Conversion to JSON could map variables to =null=,
though this may be unsafe. If the Prolog term is known to be
non-ground and JSON @null is a sensible mapping, we can also use
this simple snipit to deal with that fact.
==
term_variables(Term, Vars),
maplist(=(@null), Vars).
==
*/
%! current_json_object(Term, Module, Fields)
%
% Multifile predicate computed from the json_object/1
% declarations. Term is the most general Prolog term representing
% the object. Module is the module in which the object is defined
% and Fields is a list of f(Name, Type, Default, Var), ordered by
% Name. Var is the corresponding variable in Term.
:- multifile
json_object_to_pairs/3, % Term, Module, Pairs
current_json_object/3. % Term, Module, Fields
%! json_object(+Declaration)
%
% Declare a JSON object. The declaration takes the same format as
% using in record/1 from library(record). E.g.
%
% ==
% ?- json_object
% point(x:int, y:int, z:int=0).
% ==
%
% The type arguments are either types as know to library(error) or
% functor names of other JSON objects. The constant =any=
% indicates an untyped argument. If this is a JSON term, it
% becomes subject to json_to_prolog/2. I.e., using the type
% list(any) causes the conversion to be executed on each element
% of the list.
%
% If a field has a default, the default is used if the field is
% not specified in the JSON object. Extending the record type
% definition, types can be of the form (Type1|Type2). The type
% =null= means that the field may _not_ be present.
%
% Conversion of JSON to Prolog applies if all non-defaulted
% arguments can be found in the JSON object. If multiple rules
% match, the term with the highest arity gets preference.
json_object(Declaration) :-
throw(error(context_error(nodirective, json_object(Declaration)), _)).
%! compile_json_objects(+Spec, -Clauses) is det.
%
% Compiles a :- json_object directive into Clauses. Clauses are of
% the form:
%
% ==
% json_object_to_pairs(Term, Module, Pairs) :-
% <type-checks on Term>,
% <make Pairs from Term>.
% ==
compile_json_objects(Spec, Clauses) :-
phrase(compile_objects(Spec), Clauses).
compile_objects(A) -->
{ var(A),
!,
instantiation_error(A)
}.
compile_objects((A,B)) -->
!,
compile_objects(A),
compile_objects(B).
compile_objects(Term) -->
compile_object(Term).
compile_object(ObjectDef) -->
{ prolog_load_context(module, CM),
strip_module(CM:ObjectDef, M, Def),
extra_defs(Def, Term, ExtraFields),
Term =.. [Constructor|Args],
defaults(Args, Defs, TypedArgs),
types(TypedArgs, Names, Types)
},
record_to_json_clause(Constructor, M, Types, Names, ExtraFields),
current_clause(Constructor, M, Types, Defs, Names, ExtraFields),
[ (:- json_convert:clear_cache) ].
extra_defs(Term+Extra0, Term, Extra) :-
!,
must_be(list, Extra0),
maplist(canonical_pair, Extra0, Extra).
extra_defs(Term, Term, []).
canonical_pair(Var, _) :-
var(Var),
!,
instantiation_error(Var).
canonical_pair(Name=Value, Name=Value) :-
!,
must_be(atom, Name).
canonical_pair(Name-Value, Name=Value) :-
!,
must_be(atom, Name).
canonical_pair(NameValue, Name=Value) :-
NameValue =.. [Name,Value],
!.
canonical_pair(Pair, _) :-
type_error(pair, Pair).
%! record_to_json_clause(+Constructor, +Module, +Type, +Names)
%
% Create a clause translating the record definition into a pairs
% representation.
record_to_json_clause(Constructor, Module, Types, Names, Extra) -->
{ type_checks(Types, VarsHead, VarsBody, Body0, Module),
clean_body(Body0, Body),
Term =.. [Constructor|VarsHead],
make_pairs(Names, VarsBody, Pairs, Extra),
Head =.. [json_object_to_pairs,Term,Module,json(Pairs)]
},
[ (json_convert:(Head :- Body)) ].
%! type_checks(+Types, -VarsIn, -VarsOut, -Goal, +Module) is det.
%
% Goal is a body-term that validates Vars satisfy Types. In
% addition to the types accepted by must_be/2, it accepts =any=
% and Name/Arity. The latter demands a json_object term of the
% given Name and Arity.
%
% @tbd Compile list(Type) specification. Currently Type is
% handled like =any=
type_checks([], [], [], true, _).
type_checks([Type|T], [IV|IVars], [OV|OVars], (Goal, Body), M) :-
!,
type_check(Type, IV, OV, M, Goal),
type_checks(T, IVars, OVars, Body, M).
type_check(any, IV, OV, M, prolog_to_json(IV, OV, M)) :- !.
type_check(Name/Arity, IV, OV, M, prolog_to_json(IV, OV, M)) :-
!,
functor(IV, Name, Arity).
type_check(boolean, IV, OV, _, prolog_bool_to_json(IV, OV)) :- !.
type_check(list, IV, OV, M, prolog_list_to_json(IV, OV, M)) :- !.
type_check(list(any), IV, OV, M, prolog_list_to_json(IV, OV, M)) :- !.
type_check(list(_Type), IV, OV, M, prolog_list_to_json(IV, OV, M)) :- !.
type_check(Type, V, V, _, Goal) :-
type_goal(Type, V, Goal).
%! prolog_bool_to_json(+Prolog, -JSON) is semidet.
%
% JSON is the JSON boolean for Prolog. It is a flexible the Prolog
% notation for thruth-value, accepting one of =true=, =on= or =1=
% for @true and one of =false=, =fail=, =off= or =0= for @false.
%
% @error instantiation_error if Prolog is unbound.
prolog_bool_to_json(Var, _) :-
var(Var),
instantiation_error(Var).
prolog_bool_to_json(true, @(true)).
prolog_bool_to_json(false, @(false)).
prolog_bool_to_json(fail, @(false)).
prolog_bool_to_json(0, @(false)).
prolog_bool_to_json(on, @(true)).
prolog_bool_to_json(off, @(false)).
prolog_bool_to_json(1, @(false)).
prolog_bool_to_json(@(True), True) :-
prolog_bool_to_json(True, True).
%! type_goal(+Type, +Var, -BodyTerm) is det.
%
% Inline type checking calls.
type_goal(Type, Var, Body) :-
current_type(Type, Var, Body0),
primitive(Body0, Body),
!.
type_goal(Type, Var, is_of_type(Type, Var)).
primitive((A0,B0), (A,B)) :-
!,
primitive(A0, A),
primitive(B0, B).
primitive((A0;B0), (A,B)) :-
!,
primitive(A0, A),
primitive(B0, B).
primitive((A0->B0), (A,B)) :-
!,
primitive(A0, A),
primitive(B0, B).
primitive(_:G, G) :-
!,
predicate_property(system:G, built_in).
primitive(G, G) :-
predicate_property(system:G, built_in).
non_json_type(Type) :-
current_type(Type, _, _),
!.
%! clean_body(+BodyIn, -BodyOut) is det.
%
% Cleanup a body goal. Eliminate redundant =true= statements and
% perform partial evaluation on some commonly constructs that are
% generated from the has_type/2 clauses in library(error).
clean_body(Var, Var) :-
var(Var),
!.
clean_body((A0,B0), G) :-
!,
clean_body(A0, A),
clean_body(B0, B),
conj(A, B, G).
clean_body(ground(X), true) :- % Generated from checking extra fields.
ground(X),
!.
clean_body(memberchk(V, Values), true) :- % generated from oneof(List)
ground(V), ground(Values),
memberchk(V, Values),
!.
clean_body((integer(Low) -> If ; Then), Goal) :- % generated from between(Low,High)
number(Low),
!,
( integer(Low)
-> Goal = If
; Goal = Then
).
clean_body((A->true;fail), A) :- !. % nullable fields.
clean_body((fail->_;A), A) :- !.
clean_body(A, A).
conj(T, A, A) :- T == true, !.
conj(A, T, A) :- T == true, !.
conj(A, B, (A,B)).
make_pairs([], [], L, L).
make_pairs([N|TN], [V|TV], [N=V|T], Tail) :-
make_pairs(TN, TV, T, Tail).
%! current_clause(+Constructor, +Module, +Types, +Defs, +Names, +Extra)
%
% Create the clause current_json_object/3.
current_clause(Constructor, Module, Types, Defs, Names, Extra) -->
{ length(Types, Arity),
functor(Term, Constructor, Arity),
extra_fields(Extra, EF),
Term =.. [_|Vars],
mk_fields(Names, Types, Defs, Vars, Fields0, EF),
sort(Fields0, Fields),
Head =.. [current_json_object, Term, Module, Fields]
},
[ json_convert:Head ].
extra_fields([], []).
extra_fields([Name=Value|T0], [f(Name, oneof([Value]), _, Value)|T]) :-
extra_fields(T0, T).
mk_fields([], [], [], [], Fields, Fields).
mk_fields([Name|TN], [Type|TT], [Def|DT], [Var|VT],
[f(Name, Type, Def, Var)|T], Tail) :-
mk_fields(TN, TT, DT, VT, T, Tail).
/* The code below is copied from library(record) */
%! defaults(+ArgsSpecs, -Defaults, -Args)
%
% Strip the default specification from the argument specification.
defaults([], [], []).
defaults([Arg=Default|T0], [Default|TD], [Arg|TA]) :-
!,
defaults(T0, TD, TA).
defaults([Arg|T0], [NoDefault|TD], [Arg|TA]) :-
no_default(NoDefault),
defaults(T0, TD, TA).
no_default('$no-default$').
%! types(+ArgsSpecs, -Defaults, -Args)
%
% Strip the default specification from the argument specification.
types([], [], []).
types([Name:Type|T0], [Name|TN], [Type|TT]) :-
!,
must_be(atom, Name),
types(T0, TN, TT).
types([Name|T0], [Name|TN], [any|TT]) :-
must_be(atom, Name),
types(T0, TN, TT).
/*******************************
* PROLOG --> JSON *
*******************************/
%! prolog_to_json(:Term, -JSONObject) is det.
%
% Translate a Prolog application Term into a JSON object term.
% This transformation is based on :- json_object/1 declarations.
% If a json_object/1 declaration declares a field of type
% =boolean=, commonly used thruth-values in Prolog are converted
% to JSON booleans. Boolean translation accepts one of =true=,
% =on=, =1=, @true, =false=, =fail=, =off= or =0=, @false.
%
% @error type_error(json_term, X)
% @error instantiation_error
prolog_to_json(Module:Term, JSON) :-
prolog_to_json(Term, JSON, Module).
prolog_to_json(Var, _, _) :-
var(Var),
!,
instantiation_error(Var).
prolog_to_json(Atomic, Atomic, _) :-
atomic(Atomic),
!.
prolog_to_json(List, JSON, Module) :-
is_list(List),
!,
prolog_list_to_json(List, JSON, Module).
prolog_to_json(Record, JSON, Module) :-
record_to_pairs(Record, JSON, Module),
!.
prolog_to_json(Term, Term, _) :-
is_json_term(Term),
!.
prolog_to_json(Term, _, _) :-
type_error(json_term, Term).
record_to_pairs(T, _, _) :-
var(T),
!,
instantiation_error(T).
record_to_pairs(T, JSON, M) :-
object_module(M, Module),
json_object_to_pairs(T, Module, JSON),
!.
object_module(user, user) :- !.
object_module(M, M).
object_module(_, user).
prolog_list_to_json([], [], _).
prolog_list_to_json([H0|T0], [H|T], M) :-
prolog_to_json(H0, H, M),
prolog_list_to_json(T0, T, M).
/*******************************
* JSON --> PROLOG *
*******************************/
:- dynamic
json_to_prolog_rule/3, % Module, Pairs, Term
created_rules_for_pairs/2. % Module, Pairs
clear_cache :-
retractall(json_to_prolog_rule(_,_,_)),
retractall(created_rules_for_pairs(_,_)).
:- clear_cache.
%! json_to_prolog(+JSON, -Term) is det.
%
% Translate a JSON term into an application term. This
% transformation is based on :- json_object/1 declarations. An
% efficient transformation is non-trivial, but we rely on the
% assumption that, although the order of fields in JSON terms is
% irrelevant and can therefore vary a lot, practical applications
% will normally generate the JSON objects in a consistent order.
%
% If a field in a json_object is declared of type =boolean=, @true
% and @false are translated to =true= or =false=, the most
% commonly used Prolog representation for truth-values.
json_to_prolog(JSON, Module:Term) :-
json_to_prolog(JSON, Term, Module).
json_to_prolog(json(Pairs), Term, Module) :-
!,
( pairs_to_term(Pairs, Term, Module)
-> true
; json_pairs_to_prolog(Pairs, Prolog, Module),
Term = json(Prolog)
).
json_to_prolog(List, Prolog, Module) :-
is_list(List),
!,
json_list_to_prolog(List, Prolog, Module).
json_to_prolog(@(Special), @(Special), _) :- !.
json_to_prolog(Atomic, Atomic, _).
json_pairs_to_prolog([], [], _).
json_pairs_to_prolog([Name=JSONValue|T0], [Name=PrologValue|T], Module) :-
json_to_prolog(JSONValue, PrologValue, Module),
json_pairs_to_prolog(T0, T, Module).
json_list_to_prolog([], [], _).
json_list_to_prolog([JSONValue|T0], [PrologValue|T], Module) :-
json_to_prolog(JSONValue, PrologValue, Module),
json_list_to_prolog(T0, T, Module).
%! pairs_to_term(+Pairs, ?Term, +Module) is semidet.
%
% Convert a Name=Value set into a Prolog application term based on
% json_object/1 declarations. If multiple rules can be created,
% make the one with the highest arity the preferred one.
%
% @tbd Ignore extra pairs if term is partially given?
pairs_to_term(Pairs, Term, Module) :-
object_module(Module, M),
( json_to_prolog_rule(M, Pairs, Term)
-> !
; created_rules_for_pairs(M, Pairs)
-> !, fail
; pairs_args(Pairs, PairArgs),
sort(PairArgs, SortedPairArgs),
findall(Q-Rule,
( create_rule(SortedPairArgs, Module, M, Term0, Body, Q),
Rule = (json_to_prolog_rule(M, PairArgs, Term0) :- Body)
),
RulePairs),
keysort(RulePairs, ByQuality),
pairs_values(ByQuality, Rules),
maplist(asserta, Rules),
asserta(created_rules_for_pairs(M, PairArgs)),
json_to_prolog_rule(M, Pairs, Term), !
).
pairs_args([], []).
pairs_args([Name=_Value|T0], [Name=_|T]) :-
pairs_args(T0, T).
%! create_rule(+PairArgs, +Module, -ObjectM, -Term, -Body,
%! -Quality) is det.
%
% Create a new rule for dealing with Pairs, a Name=Value list of a
% particular order. Here is an example rule:
%
% ==
% json_to_prolog_rule([x=X, y=Y], point(X,Y)) :-
% integer(X),
% integer(Y).
% ==
%
% @arg PairArgs is an ordered list of Name=Variable pairs
% @arg Module is the module requesting the conversion
% @arg ObjectM is the module where the object is defined
% @arg Term is the converted term (with variable arguments)
% @arg Body is a Prolog goal that validates the types and
% converts arguments.
% @arg Quality is a number that indicates the matching quality.
% Larger values are better. Max is 0. There is a penalty
% of 1 for applying a default value and a penalty of 2 for
% ignoring a value in the JSON term.
create_rule(PairArgs, Module, M, Term, Body, Quality) :-
current_json_object(Term, M, Fields),
match_fields(PairArgs, Fields, Body0, Module, 0, Quality),
clean_body(Body0, Body).
match_fields(Ignored, [], true, _, Q0, Q) :-
!,
length(Ignored, Len),
Q is Q0-2*Len.
match_fields([Name=JSON|TP], [f(Name, Type, _, Prolog)|TF], (Goal,Body),
M, Q0, Q) :-
!,
match_field(Type, JSON, Prolog, M, Goal),
match_fields(TP, TF, Body, M, Q0, Q).
match_fields([Name=JSON|TP], [f(OptName, Type, Def, Prolog)|TF], Body,
M, Q0, Q) :-
OptName @< Name,
!,
( nullable(Type)
-> true
; no_default(NoDef),
Def \== NoDef
-> Prolog = Def
),
Q1 is Q0-1,
match_fields([Name=JSON|TP], TF, Body, M, Q1, Q).
match_fields([Name=_|TP], [F|TF], Body, M, Q0, Q) :-
arg(1, F, Next),
Name @< Next,
Q1 is Q0-2,
match_fields(TP, [F|TF], Body, M, Q1, Q).
nullable(null).
nullable((A|B)) :- ( nullable(A) -> true ; nullable(B) ).
match_field((A|B), JSON, Prolog, M, (BodyA->true;BodyB)) :-
!,
match_field(A, JSON, Prolog, M, BodyA),
match_field(B, JSON, Prolog, M, BodyB).
match_field(null, _, _, _, fail) :- !.
match_field(any, JSON, Prolog, M, json_to_prolog(JSON,Prolog,M)) :- !.
match_field(F/A, JSON, Prolog, M, json_to_prolog(JSON,Prolog,M)) :-
!,
functor(Prolog, F, A).
match_field(boolean, JSON, Prolog, _, json_bool_to_prolog(JSON, Prolog)) :- !.
match_field(list(Type), JSON, Prolog, M, json_list_to_prolog(JSON, Prolog, M)) :-
!,
( Type = _Funcor/_Arity
-> true
; non_json_type(Type)
-> true
; current_json_object(Term, M, _Fields),
functor(Term, Type, _)
).
match_field(list, JSON, Prolog, M, Goal) :-
!,
match_field(list(any), JSON, Prolog, M, Goal).
match_field(Type, Var, Var, _, Goal) :-
type_goal(Type, Var, Goal).
:- public json_bool_to_prolog/2.
json_bool_to_prolog(@(True), True).
/*******************************
* EXPANSION *
*******************************/
:- multifile
system:term_expansion/2.
:- dynamic
system:term_expansion/2.
system:term_expansion((:- json_object(Spec)), Clauses) :-
compile_json_objects(Spec, Clauses).