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builtins.pl
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:- module(builtins, [(=)/2, (\=)/2, (\+)/1, !/0, (',')/2, (->)/2,
(;)/2, (=..)/2, abolish/1, asserta/1, assertz/1,
at_end_of_stream/0, at_end_of_stream/1,
atom_chars/2, atom_codes/2, atom_concat/3,
atom_length/2, bagof/3, call/1, call/2, call/3,
call/4, call/5, call/6, call/7, call/8, call/9,
callable/1, catch/3, char_code/2, clause/2,
close/1, close/2, current_input/1,
current_output/1, current_op/3,
current_predicate/1, current_prolog_flag/2,
error/2, fail/0, false/0, findall/3, findall/4,
flush_output/0, flush_output/1, get_byte/1,
get_byte/2, get_char/1, get_char/2, get_code/1,
get_code/2, halt/0, halt/1, nl/0, nl/1,
number_chars/2, number_codes/2, once/1, op/3,
open/3, open/4, peek_byte/1, peek_byte/2,
peek_char/1, peek_char/2, peek_code/1,
peek_code/2, put_byte/1, put_byte/2, put_code/1,
put_code/2, put_char/1, put_char/2, read/1,
read/2, read_term/2, read_term/3, repeat/0,
retract/1, retractall/1, set_prolog_flag/2,
set_input/1, set_stream_position/2, set_output/1,
setof/3, stream_property/2, sub_atom/5,
subsumes_term/2, term_variables/2, throw/1,
true/0, unify_with_occurs_check/2, write/1,
write/2, write_canonical/1, write_canonical/2,
write_term/2, write_term/3, writeq/1, writeq/2]).
/** Builtin predicates
This library, unlike the rest, is loaded by default and it exposes the most fundamental and general
predicates of the Prolog system under the ISO standard. Basic operators, metaprogramming, exceptions,
internal settings and basic I/O are all here.
*/
% unify.
%% =(?X, ?Y)
%
% True if X and Y can be unified. This is the most basic operation of Prolog.
% Unification also happens when doing head matching in a rule.
X = X.
%% true.
%
% Always true.
true.
%% false.
%
% Always false.
false :- '$fail'.
% These are stub versions of call/{1-9} defined for bootstrapping.
% Once Scryer is bootstrapped, each is replaced with a version that
% uses expand_goal to pass the expanded goal along to '$call'.
%% call(Goal).
%
% Execute the Goal. Typically used when the Goal is not known at compile time.
call(_).
%% call(Goal, ExtraArg1).
%
% Execute the Goal with ExtraArg1 appended to the argument list. For example:
%
% ?- call(format("~s~n"), ["Alain Colmerauer"]).
% Alain Colmerauer
% true.
%
% Which is equivalent to: `format("~s~n", ["Alain Colmerauer"]).`
call(_, _).
%% call(Goal, ExtraArg1, ExtraArg2).
%
% Execute Goal with ExtraArg1 and ExtraArg2 appended to the argument list.
call(_, _, _).
%% call(Goal, ExtraArg1, ExtraArg2, ExtraArg3).
%
% Execute Goal with ExtraArg1, ExtraArg2 and ExtraArg3 appended to the argument list.
call(_, _, _, _).
%% call(Goal, ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4).
%
% Execute Goal with ExtraArg1, ExtraArg2, ExtraArg3 and ExtraArg4 appended to the argument list.
call(_, _, _, _, _).
%% call(Goal, ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5).
%
% Execute Goal with ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4 and ExtraArg5 appended to the argument list.
call(_, _, _, _, _, _).
%% call(Goal, ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5, ExtraArg6).
%
% Execute Goal with ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5 and ExtraArg6 appended
% to the argument list.
call(_, _, _, _, _, _, _).
%% call(Goal, ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5, ExtraArg6, ExtraArg7).
%
% Execute Goal with ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5, ExtraArg6 and ExtraArg7
% appended to the argument list.
call(_, _, _, _, _, _, _, _).
%% call(Goal, ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5, ExtraArg6, ExtraArg7, ExtraArg8).
%
% Execute Goal with ExtraArg1, ExtraArg2, ExtraArg3, ExtraArg4, ExtraArg5, ExtraArg6, ExtraArg7 and
% ExtraArg8, appended to the argument list.
call(_, _, _, _, _, _, _, _, _).
:- meta_predicate catch(0, ?, 0).
% flags.
%% current_prolog_flag(Flag, Value)
%
% True iff Flag is a flag supported by the processor, and Value is the value currently associated with it.
% A flag is a setting which value affects internal operation of the Prolog system. Some flags are read-only,
% while others can be set with `set_prolog_flag/2`.
%
% The flags that Scryer Prolog support are:
%
% * `max_arity`: The max arity a predicate can have in Prolog. On Scryer is set to 1023. Read only.
% * `bounded`: `true` if integer arithmethic is bounded between some min/max values. On Scryer is always set
% to `false` since it supports unbounded integer arithmethic. Read only.
% * `integer_rounding_function`: Describes the rounding donde by `//` and `rem` functions. On Scryer is
% always set to `toward_zero`. Read only
% * `double_quotes`: Determines how double quoted strings are read by Prolog. Scryer uses `chars` by default
% which is a list of one-character atoms. Other values are codes (list of integers representing characters),
% and atom which creates a whole atom for the string value. Read and write.
% * `max_integer`: Maximum integer supported by the system. As Scryer Prolog has unbounded integer arithmethic,
% checking the value of this flag fails. Read only.
% * `min_integer`: Minimum integer supported by the system. As Scryer Prolog has unbounded integer arithmethic,
% checking the value of this flag fails. Read only.
% * `occurs_check`: Returns if the occurs check is enabled. The occurs check prevents the creation cyclic terms.
% Historically the Prolog unification algorithm didn't do that check so changing the value modifies how Prolog
% operates in the low-level. Possible values are `false` (default), `true` (unification has this check
% enabled) and `error` which throws an exception when a cylic term is created. Read and write.
% * `unknown`: How undefined predicates are handled when called. Possible values are `error` (the default, an error is thrown),
% `fail` (the call silently fails) and `warn` (the call fails and a warning about the undefined predicate is printed).
% * `answer_write_options`: Additional write options used by the top level for writing answers.
%
current_prolog_flag(Flag, Value) :- Flag == max_arity, !, Value = 1023.
current_prolog_flag(max_arity, 1023).
current_prolog_flag(Flag, Value) :- Flag == bounded, !, Value = false.
current_prolog_flag(bounded, false).
current_prolog_flag(Flag, Value) :- Flag == integer_rounding_function, !, Value == toward_zero.
current_prolog_flag(integer_rounding_function, toward_zero).
current_prolog_flag(Flag, Value) :- Flag == double_quotes, !, '$get_double_quotes'(Value).
current_prolog_flag(double_quotes, Value) :- '$get_double_quotes'(Value).
current_prolog_flag(Flag, Value) :- Flag == unknown, !, '$get_unknown'(Value).
current_prolog_flag(unknown, Value) :- '$get_unknown'(Value).
current_prolog_flag(Flag, _) :- Flag == max_integer, !, '$fail'.
current_prolog_flag(Flag, _) :- Flag == min_integer, !, '$fail'.
current_prolog_flag(Flag, OccursCheckEnabled) :-
Flag == occurs_check,
!,
'$is_sto_enabled'(OccursCheckEnabled).
current_prolog_flag(occurs_check, OccursCheckEnabled) :-
'$is_sto_enabled'(OccursCheckEnabled).
current_prolog_flag(Flag, Value) :-
Flag == answer_write_options,
!,
answer_write_options(Value).
current_prolog_flag(answer_write_options, Value) :-
answer_write_options(Value).
current_prolog_flag(Flag, _) :-
atom(Flag),
throw(error(domain_error(prolog_flag, Flag), current_prolog_flag/2)). % 8.17.2.3 b
current_prolog_flag(Flag, _) :-
nonvar(Flag),
throw(error(type_error(atom, Flag), current_prolog_flag/2)). % 8.17.2.3 a
answer_write_options(Value) :-
( iso_ext:bb_get('$answer_write_options', Value) -> true
; Value = []
).
%% set_prolog_flag(Flag, Value).
%
% Sets the internal value of the flag. To see the list of flags supported by Scryer Prolog,
% check `current_prolog_flag/2`. The flags that are read only will fail if you try to change their values
set_prolog_flag(Flag, Value) :-
(var(Flag) ; var(Value)),
throw(error(instantiation_error, set_prolog_flag/2)). % 8.17.1.3 a, b
set_prolog_flag(bounded, false) :- !. % 7.11.1.1
set_prolog_flag(bounded, true) :- !, '$fail'. % 7.11.1.1
set_prolog_flag(bounded, Value) :-
throw(error(domain_error(flag_value, bounded + Value), set_prolog_flag/2)). % 8.17.1.3 e
set_prolog_flag(max_integer, Value) :- integer(Value), !, '$fail'. % 7.11.1.2
set_prolog_flag(max_integer, Value) :-
throw(error(domain_error(flag_value, max_integer + Value), set_prolog_flag/2)). % 8.17.1.3 e
set_prolog_flag(min_integer, Value) :- integer(Value), !, '$fail'. % 7.11.1.3
set_prolog_flag(min_integer, Value) :-
throw(error(domain_error(flag_value, min_integer + Value), set_prolog_flag/2)). % 8.17.1.3 e
set_prolog_flag(integer_rounding_function, down) :- !. % 7.11.1.4
set_prolog_flag(integer_rounding_function, Value) :-
throw(error(domain_error(flag_value, integer_rounding_function + Value),
set_prolog_flag/2)). % 8.17.1.3 e
set_prolog_flag(double_quotes, chars) :-
!, '$set_double_quotes'(chars). % 7.11.2.5, list of one-char atoms.
set_prolog_flag(double_quotes, atom) :-
!, '$set_double_quotes'(atom). % 7.11.2.5, list of char codes (UTF8).
set_prolog_flag(double_quotes, codes) :-
!, '$set_double_quotes'(codes).
set_prolog_flag(unknown, error) :-
!, '$set_unknown'(error).
set_prolog_flag(unknown, warning) :-
!, '$set_unknown'(warning).
set_prolog_flag(unknown, fail) :-
!, '$set_unknown'(fail).
set_prolog_flag(occurs_check, true) :-
!, '$set_sto_as_unify'.
set_prolog_flag(occurs_check, false) :-
!, '$set_nsto_as_unify'.
set_prolog_flag(occurs_check, error) :-
!, '$set_sto_with_error_as_unify'.
set_prolog_flag(double_quotes, Value) :-
flag_domain_error(double_quotes, Value).
set_prolog_flag(answer_write_options, Options) :-
!,
catch(catch(builtins:parse_write_options(Options, _, set_prolog_flag/2),
error(domain_error(_,_), _),
throw(error(type_error(_,_), _))), % convert domain error to type error ....
error(type_error(_,_), _), % ... to catch type and domain errors.
flag_domain_error(answer_write_options, Options)),
iso_ext:bb_put('$answer_write_options', Options).
set_prolog_flag(Flag, _) :-
atom(Flag),
throw(error(domain_error(prolog_flag, Flag), set_prolog_flag/2)). % 8.17.1.3 d
set_prolog_flag(Flag, _) :-
throw(error(type_error(atom, Flag), set_prolog_flag/2)). % 8.17.1.3 c
flag_domain_error(Flag, Value) :-
% domain error via 8.17.1.3 e: Value is inappropriate for Flag
throw(error(domain_error(flag_value, Flag + Value), set_prolog_flag/2)).
% control operators.
%% fail.
%
% A predicate that always fails. The more declarative `false/0` should be used instead.
fail :- '$fail'.
:- meta_predicate \+(0).
%% \+(Goal)
%
% True iff Goal fails
\+ G :- call(G), !, '$fail'.
\+ _.
%% \=(?X, ?Y)
%
% True iff X and Y can't be unified
X \= X :- !, '$fail'.
_ \= _.
:- meta_predicate once(0).
%% once(Goal)
%
% Execute Goal (like `call/1`) but exactly once, ignoring any kind of alternative solutions the original predicate
% could have generated.
once(G) :- call(G), !.
%% repeat.
%
% This predicate succeeds arbitrarily often, generating choice points with that.
repeat.
repeat :- repeat.
:- meta_predicate ','(0,0).
:- meta_predicate ;(0,0).
:- meta_predicate ->(0,0).
%% ->(G1, G2)
%
% If-then and if-then-else constructs
:- non_counted_backtracking (->)/2.
G1 -> G2 :- control_entry_point((G1 -> G2)).
:- non_counted_backtracking staggered_if_then/2.
staggered_if_then(G1, G2) :-
call(G1),
!,
call(G2).
%% ;(G1, G2)
%
% Disjunction (or)
:- non_counted_backtracking (;)/2.
G1 ; G2 :- control_entry_point((G1 ; G2)).
:- non_counted_backtracking staggered_sc/2.
staggered_sc(G, _) :-
( nonvar(G),
G = '$call'(builtins:staggered_if_then(G1, G2)) ->
call(G1),
!,
call(G2)
; call(G)
).
staggered_sc(_, G) :- call(G).
%% !.
%
% Cut operator. Discards the choicepoints created since entering the prediacate in which the operator appears.
% Using cut is not recommended as it introduces a non-declarative flow of programming and makes it more difficult
% to reason about the programs. Also restricts the ability to run the program with alternative execution strategies
!.
:- non_counted_backtracking get_cp/1.
get_cp(B) :- '$get_cp'(B).
:- non_counted_backtracking set_cp/1.
set_cp(B) :- '$set_cp'(B).
%% ,(G1, G2)
%
% Conjuction (and)
:- non_counted_backtracking (',')/2.
','(G1, G2) :- control_entry_point((G1, G2)).
:- non_counted_backtracking control_entry_point/1.
control_entry_point(G) :-
functor(G, Name, Arity),
'$get_cp'(B),
catch('$call'(builtins:dispatch_prep(G,B,Conts)),
dispatch_prep_error,
'$call'(builtins:throw(error(type_error(callable, G), Name/Arity)))),
dispatch_call_list(Conts).
:- non_counted_backtracking cont_list_to_goal/2.
cont_list_goal([Cont], Cont) :- !.
cont_list_goal(Conts, '$call'(builtins:dispatch_call_list(Conts))).
:- non_counted_backtracking dispatch_prep/3.
dispatch_prep(Gs, B, Conts) :-
( callable(Gs) ->
loader:strip_module(Gs, M, Gs0),
( nonvar(Gs0),
dispatch_prep_(Gs0, B, Conts) ->
true
; Gs0 == ! ->
Conts = ['$call'(builtins:set_cp(B))]
; nonvar(Gs0),
\+ callable(Gs0) ->
throw(dispatch_prep_error)
; Conts = [Gs]
)
; var(Gs) ->
Conts = [Gs]
; throw(dispatch_prep_error)
).
:- non_counted_backtracking dispatch_prep_/3.
dispatch_prep_((G1, G2), B, [Cont|Conts]) :-
dispatch_prep(G1, B, IConts1),
cont_list_goal(IConts1, Cont),
dispatch_prep(G2, B, Conts).
dispatch_prep_((G1 ; G2), B, Conts) :-
( nonvar(G1) ->
( G1 = (G11 -> G12) ->
dispatch_prep(G11, B, IConts2),
dispatch_prep(G12, B, IConts3),
cont_list_goal(IConts2, Cont2),
cont_list_goal(IConts3, Cont3),
Cont0 = '$call'(builtins:staggered_if_then(Cont2, Cont3))
; dispatch_prep(G1, B, IConts0),
dispatch_prep(G2, B, IConts1),
cont_list_goal(IConts0, Cont0)
)
; dispatch_prep(G1, B1, IConts0),
cont_list_goal(IConts0, Cont0)
),
dispatch_prep(G2, B, IConts1),
cont_list_goal(IConts0, Cont0),
cont_list_goal(IConts1, Cont1),
Conts = ['$call'(builtins:staggered_sc(Cont0, Cont1))].
dispatch_prep_((G1 -> G2), B, Conts) :-
dispatch_prep(G1, B1, IConts1),
dispatch_prep(G2, B, IConts2),
cont_list_goal(IConts1, Cont1),
cont_list_goal(IConts2, Cont2),
Conts = ['$call'(builtins:get_cp(B1)),
'$call'(builtins:staggered_if_then(Cont1, Cont2))].
:- non_counted_backtracking dispatch_call_list/1.
dispatch_call_list([]).
dispatch_call_list([G1,G2,G3,G4,G5,G6,G7,G8|Gs]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)),
'$call_with_inference_counting'(call(G3)),
'$call_with_inference_counting'(call(G4)),
'$call_with_inference_counting'(call(G5)),
'$call_with_inference_counting'(call(G6)),
'$call_with_inference_counting'(call(G7)),
'$call_with_inference_counting'(call(G8)),
dispatch_call_list(Gs).
dispatch_call_list([G1,G2,G3,G4,G5,G6,G7]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)),
'$call_with_inference_counting'(call(G3)),
'$call_with_inference_counting'(call(G4)),
'$call_with_inference_counting'(call(G5)),
'$call_with_inference_counting'(call(G6)),
'$call_with_inference_counting'(call(G7)).
dispatch_call_list([G1,G2,G3,G4,G5,G6]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)),
'$call_with_inference_counting'(call(G3)),
'$call_with_inference_counting'(call(G4)),
'$call_with_inference_counting'(call(G5)),
'$call_with_inference_counting'(call(G6)).
dispatch_call_list([G1,G2,G3,G4,G5]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)),
'$call_with_inference_counting'(call(G3)),
'$call_with_inference_counting'(call(G4)),
'$call_with_inference_counting'(call(G5)).
dispatch_call_list([G1,G2,G3,G4]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)),
'$call_with_inference_counting'(call(G3)),
'$call_with_inference_counting'(call(G4)).
dispatch_call_list([G1,G2,G3]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)),
'$call_with_inference_counting'(call(G3)).
dispatch_call_list([G1,G2]) :-
!,
'$call_with_inference_counting'(call(G1)),
'$call_with_inference_counting'(call(G2)).
dispatch_call_list([G1]) :-
'$call_with_inference_counting'(call(G1)).
% univ.
:- non_counted_backtracking univ_errors/3.
univ_errors(Term, List, N) :-
'$skip_max_list'(N, _, List, R),
( var(R) ->
( var(Term),
throw(error(instantiation_error, (=..)/2)) % 8.5.3.3 a)
; true
)
; R \== [] ->
throw(error(type_error(list, List), (=..)/2)) % 8.5.3.3 b)
; List = [H|T] ->
( var(H),
var(Term), % R == [] => List is a proper list.
throw(error(instantiation_error, (=..)/2)) % 8.5.3.3 c)
; T \== [],
nonvar(H),
\+ atom(H),
throw(error(type_error(atom, H), (=..)/2)) % 8.5.3.3 d)
; compound(H),
T == [],
throw(error(type_error(atomic, H), (=..)/2)) % 8.5.3.3 e)
; var(Term),
current_prolog_flag(max_arity, M),
N - 1 > M,
throw(error(representation_error(max_arity), (=..)/2)) % 8.5.3.3 g)
; true
)
; var(Term) ->
throw(error(domain_error(non_empty_list, List), (=..)/2)) % 8.5.3.3 f)
; true
).
:- non_counted_backtracking (=..)/2.
%% =..(Term, List)
%
% Univ operator. True iff Term is a term whose functor is the head of the List, and the rest of arguments of Term
% are in tail of the List. Example:
%
% ?- f(a, X) =.. List.
% List = [f,a,X].
Term =.. List :-
univ_errors(Term, List, N),
univ_worker(Term, List, N).
:- non_counted_backtracking univ_worker/3.
univ_worker(Term, List, _) :-
atomic(Term),
!,
List = [Term].
univ_worker(Term, [Name|Args], N) :-
var(Term),
!,
Arity is N-1,
functor(Term, Name, Arity), % Term = {var}, Name = nonvar, Arity = 0.
get_args(Args, Term, 1, Arity).
univ_worker(Term, List, _) :-
functor(Term, Name, Arity),
get_args(Args, Term, 1, Arity),
List = [Name|Args].
:- non_counted_backtracking get_args/4.
get_args(Args, _, _, 0) :-
!,
Args = [].
get_args([Arg], Func, N, N) :-
!,
arg(N, Func, Arg).
get_args([Arg|Args], Func, I0, N) :-
arg(I0, Func, Arg),
I1 is I0 + 1,
get_args(Args, Func, I1, N).
:- meta_predicate parse_options_list(?, 2, ?, ?, ?).
parse_options_list(Options, Selector, DefaultPairs, OptionValues, Stub) :-
'$skip_max_list'(_, _, Options, Tail),
( Tail == [] ->
true
; var(Tail) ->
throw(error(instantiation_error, Stub)) % 8.11.5.3c)
; Tail \== [] ->
throw(error(type_error(list, Options), Stub)) % 8.11.5.3e)
),
( lists:maplist('$call'(nonvar), Options), % need '$call' because
% maplist isn't
% declared as a
% meta-predicate yet
catch(lists:maplist(Selector, Options, OptionPairs0),
error(E, _),
builtins:throw(error(E, Stub))) ->
lists:append(DefaultPairs, OptionPairs0, OptionPairs1),
keysort(OptionPairs1, OptionPairs),
select_rightmost_options(OptionPairs, OptionValues)
;
throw(error(instantiation_error, Stub)) % 8.11.5.3c)
).
parse_write_options(Options, OptionValues, Stub) :-
DefaultOptions = [double_quotes-false, ignore_ops-false, max_depth-0, numbervars-false,
quoted-false, variable_names-[]],
parse_options_list(Options, builtins:parse_write_options_, DefaultOptions, OptionValues, Stub).
parse_write_options_(double_quotes(DoubleQuotes), double_quotes-DoubleQuotes) :-
( var(DoubleQuotes) ->
throw(error(instantiation_error, _))
; lists:member(DoubleQuotes, [true, false]),
!
; throw(error(domain_error(write_option, double_quotes(DoubleQuotes)), _))
).
parse_write_options_(ignore_ops(IgnoreOps), ignore_ops-IgnoreOps) :-
( var(IgnoreOps) ->
throw(error(instantiation_error, _))
; lists:member(IgnoreOps, [true, false]),
!
; throw(error(domain_error(write_option, ignore_ops(IgnoreOps)), _))
).
parse_write_options_(quoted(Quoted), quoted-Quoted) :-
( var(Quoted) ->
throw(error(instantiation_error, _))
; lists:member(Quoted, [true, false]),
!
; throw(error(domain_error(write_option, quoted(Quoted)), _))
).
parse_write_options_(numbervars(NumberVars), numbervars-NumberVars) :-
( var(NumberVars) ->
throw(error(instantiation_error, _))
; lists:member(NumberVars, [true, false]),
!
; throw(error(domain_error(write_option, numbervars(NumberVars)), _))
).
parse_write_options_(variable_names(VNNames), variable_names-VNNames) :-
must_be_var_names_list(VNNames),
!.
parse_write_options_(max_depth(MaxDepth), max_depth-MaxDepth) :-
( var(MaxDepth) ->
throw(error(instantiation_error, _))
; integer(MaxDepth),
MaxDepth >= 0,
!
; throw(error(domain_error(write_option, max_depth(MaxDepth)), _))
).
parse_write_options_(E, _) :-
throw(error(domain_error(write_option, E), _)).
must_be_var_names_list(VarNames) :-
'$skip_max_list'(_, _, VarNames, Tail),
( Tail == [] ->
must_be_var_names_list_(VarNames, VarNames)
; var(Tail) ->
throw(error(instantiation_error, write_term/2))
; throw(error(domain_error(write_option, variable_names(VarNames)), write_term/2))
).
must_be_var_names_list_([], List).
must_be_var_names_list_([VarName | VarNames], List) :-
( nonvar(VarName) ->
( VarName = (Atom = _) ->
( atom(Atom) ->
must_be_var_names_list_(VarNames, List)
; var(Atom) ->
throw(error(instantiation_error, write_term/2))
; throw(error(domain_error(write_option, variable_names(List)), write_term/2))
)
; throw(error(domain_error(write_option, variable_names(List)), write_term/2))
)
; throw(error(instantiation_error, write_term/2))
).
%% write_term(+Term, +Options).
%
% Write Term to the current output stream according to some output syntax options.
% Options are specified in detail in `write_term/3`.
write_term(Term, Options) :-
current_output(Stream),
write_term(Stream, Term, Options).
%% write_term(+Stream, +Term, +Options).
%
% Write Term to the stream Stream according to some output syntax options. The options available are:
%
% * `ignore_ops(+Boolean)` if `true`, the generic term representation is used everywhere. In `false`
% (default), operators do not use that generic term representation.
% * `max_depth(+N)` if the term is nested deeper than N, print the reminder as ellipses.
% If N = 0 (default), there's no limit.
% * `numbervars(+Boolean)` if true, replaces `$VAR(N)` variables with letters, in order. Default is false.
% * `quoted(+Boolean)` if true, strings and atoms that need quotes to be valid Prolog syntax, are quoted. Default is false.
% * `variable_names(+List)` assign names to variables in term. List should be a list of terms of format `Name=Var`.
% * `double_quotes(+Boolean)` if true, strings are printed in double quotes rather than with list notation. Default is false.
write_term(Stream, Term, Options) :-
parse_write_options(Options, [DoubleQuotes, IgnoreOps, MaxDepth, NumberVars, Quoted, VNNames], write_term/3),
'$write_term'(Stream, Term, IgnoreOps, NumberVars, Quoted, VNNames, MaxDepth, DoubleQuotes).
%% write(+Term).
%
% Write Term to the current output stream using a syntax similar to Prolog
write(Term) :-
current_output(Stream),
'$write_term'(Stream, Term, false, true, false, [], 0, false).
%% write(+Stream, +Term).
%
% Write Term to the stream Stream using a syntax similar to Prolog
write(Stream, Term) :-
'$write_term'(Stream, Term, false, true, false, [], 0, false).
%% write_canonical(+Term).
%
% Write Term to the current output stream using canonical Prolog syntax. Can be read back as Prolog terms.
write_canonical(Term) :-
current_output(Stream),
'$write_term'(Stream, Term, true, false, true, [], 0, false).
%% write_canonical(+Stream, +Term).
%
% Write Term to the stream Stream using canonical Prolog syntax. Can be read back as Prolog terms.
write_canonical(Stream, Term) :-
'$write_term'(Stream, Term, true, false, true, [], 0, false).
%% writeq(+Term).
%
% Write Term to the current output stream using a syntax similar to `write/1` but quoting the atoms that need to be
% quoted according to Prolog syntax.
writeq(Term) :-
current_output(Stream),
'$write_term'(Stream, Term, false, true, true, [], 0, false).
%% writeq(+Stream, +Term).
%
% Write Term to the stream Stream using a syntax similar to `write/1` but quoting the atoms that need to be
% quoted according to Prolog syntax.
writeq(Stream, Term) :-
'$write_term'(Stream, Term, false, true, true, [], 0, false).
select_rightmost_options([Option-Value | OptionPairs], OptionValues) :-
( pairs:same_key(Option, OptionPairs, OtherValues, _),
OtherValues == [] ->
OptionValues = [Value | OptionValues0],
select_rightmost_options(OptionPairs, OptionValues0)
;
select_rightmost_options(OptionPairs, OptionValues)
).
select_rightmost_options([], []).
parse_read_term_options(Options, OptionValues, Stub) :-
DefaultOptions = [singletons-_, variables-_, variable_names-_],
parse_options_list(Options, builtins:parse_read_term_options_, DefaultOptions, OptionValues, Stub).
parse_read_term_options_(singletons(Vars), singletons-Vars) :- !.
parse_read_term_options_(variables(Vars), variables-Vars) :- !.
parse_read_term_options_(variable_names(Vars), variable_names-Vars) :- !.
parse_read_term_options_(E,_) :-
throw(error(domain_error(read_option, E), _)).
%% read_term(+Stream, -Term, +Options).
%
% Read Term from the stream Stream. It supports several options:
% * `variables(-Vars)` unifies Vars with a list of variables in the term. Similar to do `term_variables/2` with the new term.
% * `variable_names(-Vars)` unifies Vars with a list `Name=Var` with Name describing the variable name and Var the variable itself that appears in Term.
% * `singletons` similar to `variable_names` but only reports variables occurring only once in Term.
read_term(Stream, Term, Options) :-
parse_read_term_options(Options, [Singletons, VariableNames, Variables], read_term/3),
'$read_term'(Stream, Term, Singletons, Variables, VariableNames).
%% read_term(-Term, +Options).
%
% Read Term from the current input stream. It supports several options described in more detail in `read_term/3`.
read_term(Term, Options) :-
current_input(Stream),
read_term(Stream, Term, Options).
%% read(-Term).
%
% Read Term from the current input stream with default options. **NOTE** This is not a general predicate
% to read input from a file or the user. Use other predicates like `phrase_from_file/2` for that.
read(Term) :-
current_input(Stream),
read_term(Stream, Term, []).
% read(Stream, Term).
%% read(+Stream, -Term).
%
% Same as read_term/3 with all default options.
read(Stream, Term) :-
read_term(Stream, Term, []).
% ensures List is either a variable or a list.
can_be_list(List, _) :-
var(List),
!.
can_be_list(List, _) :-
'$skip_max_list'(_, _, List, Tail),
( var(Tail) ->
true
; Tail == []
),
!.
can_be_list(List, PI) :-
throw(error(type_error(list, List), PI)).
% term_variables.
%% term_variables(+Term, -Vars).
%
% True iff given a Term, Vars is a list of all the unique variables that appear in Term. The variables are sorted depth-first
% and left-to-right.
%
% ?- term_variables(f(X, Y, X, g(Z)), Vars).
% Vars = [X, Y, Z].
term_variables(Term, Vars) :-
can_be_list(Vars, term_variables/2),
'$term_variables'(Term, Vars).
% exceptions.
:- non_counted_backtracking catch/3.
%% catch(Goal, Catcher, Recover).
%
% Calls Goal, but if it throws an exception that unifies with Catcher, Recover will be called instead
% and the program will be resumed. Example:
%
% ```
% ?- catch(number_chars(X, "not_a_number"), error(syntax_error(_), _), X = 0).
% X = 0.
% ```
catch(G,C,R) :-
'$get_current_block'(Bb),
catch(G,C,R,Bb).
:- meta_predicate catch(0, ?, 0, ?).
:- non_counted_backtracking catch/4.
catch(G,C,R,Bb) :-
'$install_new_block'(NBb),
call(G),
end_block(Bb, NBb).
catch(G,C,R,Bb) :-
'$reset_block'(Bb),
'$get_ball'(Ball),
'$push_ball_stack', % move ball to ball stack.
handle_ball(Ball, C, R).
:- non_counted_backtracking end_block/2.
end_block(Bb, NBb) :-
'$clean_up_block'(NBb),
'$reset_block'(Bb).
end_block(_Bb, NBb) :-
'$reset_block'(NBb),
'$fail'.
:- non_counted_backtracking handle_ball/3.
handle_ball(C, C, R) :-
!,
'$pop_ball_stack', % remove ball from ball stack.
call(R).
handle_ball(_, _, _) :-
'$pop_from_ball_stack', % restore ball from ball stack.
'$unwind_stack'.
:- non_counted_backtracking throw/1.
%% throw(+Exception).
%
% Raise the exception Exception. The system looks for the innermost `catch/3` for which Exception
% unifies with Catcher. Example:
%
% ```
% ?- throw(custom_error(42)).
% throw(custom_error(42)).
% ?- catch(throw(custom_error(42)), custom_error(_), true).
% true.
% ```
throw(Ball) :-
( var(Ball) ->
'$set_ball'(error(instantiation_error,throw/1))
; '$set_ball'(Ball)
),
'$unwind_stack'.
:- non_counted_backtracking '$iterate_find_all'/4.
'$iterate_find_all'(Template, Goal, _, LhOffset) :-
'$call_with_inference_counting'(call(Goal)),
'$copy_to_lh'(LhOffset, Template),
'$fail'.
'$iterate_find_all'(_, _, Solutions, LhOffset) :-
'$truncate_if_no_lh_growth'(LhOffset),
'$get_lh_from_offset'(LhOffset, Solutions).
truncate_lh_to(LhLength) :- '$truncate_lh_to'(LhLength).
:- meta_predicate findall(?, 0, ?).
:- non_counted_backtracking findall_cleanup/2.
findall_cleanup(LhLength, Error) :-
truncate_lh_to(LhLength),
throw(Error).
:- non_counted_backtracking findall/3.
%% findall(Template, Goal, Solutions).
%
% Unify Solutions with a list of all values that variables in Template can take in Goal.
% `findall/3` is equivalent to `bagof/3` with all free variables scoped to the Goal (`^` operator)
% except that `bagof/3` fails when no solutions are found and `findall/3` unifies with an empty list.
% Example:
%
% ```
% f(1,2).
% f(1,3).
% f(1,4).
% ?- findall(X-Y, f(X, Y), Solutions).
% Solutions = [1-2,1-3,1-4].
% ```
findall(Template, Goal, Solutions) :-
error:can_be(list, Solutions),
'$lh_length'(LhLength),
catch(builtins:'$iterate_find_all'(Template, Goal, Solutions, LhLength),
Error,
builtins:findall_cleanup(LhLength, Error)
).
:- non_counted_backtracking '$iterate_find_all_diff'/5.
'$iterate_find_all_diff'(Template, Goal, _, _, LhOffset) :-
'$call_with_inference_counting'(call(Goal)),
'$copy_to_lh'(LhOffset, Template),
'$fail'.
'$iterate_find_all_diff'(_, _, Solutions0, Solutions1, LhOffset) :-
'$truncate_if_no_lh_growth_diff'(LhOffset, Solutions1),
'$get_lh_from_offset_diff'(LhOffset, Solutions0, Solutions1).
:- meta_predicate findall(?, 0, ?, ?).
:- non_counted_backtracking findall/4.
%% findall(Template, Goal, Solutions0, Solutions1)
%
% Similar to `findall/3` but returns the solutions as the difference list Solutions0-Solutions1.
findall(Template, Goal, Solutions0, Solutions1) :-
error:can_be(list, Solutions0),
error:can_be(list, Solutions1),
'$lh_length'(LhLength),
catch(builtins:'$iterate_find_all_diff'(Template, Goal, Solutions0,
Solutions1, LhLength),
Error,
builtins:findall_cleanup(LhLength, Error)
).
:- non_counted_backtracking set_difference/3.
set_difference([X|Xs], [Y|Ys], Zs) :-
X == Y, !, set_difference(Xs, [Y|Ys], Zs).
set_difference([X|Xs], [Y|Ys], [X|Zs]) :-
X @< Y, !, set_difference(Xs, [Y|Ys], Zs).
set_difference([X|Xs], [Y|Ys], Zs) :-
X @> Y, !, set_difference([X|Xs], Ys, Zs).
set_difference([], _, []) :- !.
set_difference(Xs, [], Xs).
% variant/2 checks whether X is a variant of Y per the definition in
% 7.1.6.1 of the ISO standard.
:- non_counted_backtracking variant/4.
variant(X,Y,VPs,VPs0) :-
( var(X) ->
var(Y),
VPs = [X-Y|VPs0]
; var(Y) ->
false
; X =.. [FX | XArgs],
Y =.. [FX | YArgs],
lists:foldl('$call'(builtins:variant), XArgs, YArgs, VPs, VPs0)
).
:- non_counted_backtracking variant/2.
singleton([_]).
variant(X, Y) :-
variant(X,Y, VPs, []),
keysort(VPs, SVPs),
pairs:group_pairs_by_key(SVPs, SVPKs),
pairs:pairs_values(SVPKs, Vals),
lists:maplist('$call'(builtins:term_variables), Vals, Vs),
lists:maplist('$call'(builtins:singleton), Vs),
term_variables(Vs, YVars),
lists:length(SVPKs, N),
lists:length(YVars, N).
:- non_counted_backtracking group_by_variant/4.
group_by_variant([V2-S2 | Pairs], V1-S1, [S2 | Solutions], Pairs0) :-
variant(V1, V2),
!,
V1 = V2,
group_by_variant(Pairs, V2-S2, Solutions, Pairs0).
group_by_variant(Pairs, _, [], Pairs).
:- non_counted_backtracking group_by_variants/2.