:- module(builtins, [(=)/2, (\=)/2, (\+)/1, !/0, (',')/2, (->)/2, (;)/2,
                     (=..)/2, (:)/2, (:)/3, (:)/4, (:)/5, (:)/6,
                     (:)/7, (:)/8, (:)/9, (:)/10, (:)/11, (:)/12,
                     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,
                     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_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]).


% unify.
X = X.

true.

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(G) :- '$call'(G).

call(G, A) :- '$call'(G, A).

call(G, A, B) :- '$call'(G, A, B).

call(G, A, B, C) :- '$call'(G, A, B, C).

call(G, A, B, C, D) :- '$call'(G, A, B, C, D).

call(G, A, B, C, D, E) :- '$call'(G, A, B, C, D, E).

call(G, A, B, C, D, E, F) :- '$call'(G, A, B, C, D, E, F).

call(G, A, B, C, D, E, F, G) :- '$call'(G, A, B, C, D, E, F, G).

call(G, A, B, C, D, E, F, G, H) :- '$call'(G, A, B, C, D, E, F, G, H).

% dynamic module resolution.

Module : Predicate :-
    (  atom(Module) -> '$module_call'(Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1) :-
    (  atom(Module) ->
       '$module_call'(A1, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2) :-
    (  atom(Module) -> '$module_call'(A1, A2, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4, A5) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, A5, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4, A5, A6) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, A5, A6, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4, A5, A6, A7) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, A5, A6, A7, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4, A5, A6, A7, A8) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, A5, A6, A7, A8, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4, A5, A6, A7, A8, A9) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, A5, A6, A7, A8, A9, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

:(Module, Predicate, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10) :-
    (  atom(Module) -> '$module_call'(A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, Module, Predicate)
    ;  throw(error(type_error(atom, Module), (:)/2))
    ).

% flags.

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, _) :- 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(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

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(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) :-
    throw(error(domain_error(flag_value, double_quotes + Value),
                set_prolog_flag/2)). % 8.17.1.3 e
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

% control operators.

fail :- '$fail'.


:- meta_predicate \+(0).

\+ G :- call(G), !, false.
\+ _.


X \= X :- !, false.
_ \= _.


:- meta_predicate once(0).

once(G) :- call(G), !.


repeat.
repeat :- repeat.


:- meta_predicate ','(0,0).

:- meta_predicate ;(0,0).

:- meta_predicate ->(0,0).

! :- '$get_staggered_cp'(B), '$set_cp'(B).

G1 -> G2 :- '$get_staggered_cp'(B), call('$call'(G1)), '$set_cp'(B), call('$call'(G2)).

G ; _ :- call('$call'(G)).
_ ; G :- call('$call'(G)).

','(G1, G2) :- '$get_staggered_cp'(B), comma_dispatch(G1,G2,B).

set_cp(B) :- '$set_cp'(B).

:- non_counted_backtracking comma_dispatch/3.

comma_dispatch(G1, G2, B) :-
    comma_dispatch_prep((G1, G2), B, Conts),
    comma_dispatch_call_list(Conts).

:- non_counted_backtracking cont_list_to_goal/2.

cont_list_goal([Cont], Cont) :- !.
cont_list_goal(Conts, builtins:comma_dispatch_call_list(Conts)).

:- non_counted_backtracking comma_dispatch_prep/3.

comma_dispatch_prep(Gs, B, [Cont|Conts]) :-
    (  callable(Gs) ->
       (  functor(Gs, ',', 2) ->
          arg(1, Gs, G1),
          arg(2, Gs, G2),
          comma_dispatch_prep(G1, B, IConts1),
          cont_list_goal(IConts1, Cont),
          comma_dispatch_prep(G2, B, Conts)
       ;  ( Gs = ! ; Gs = _:! ) ->
          Cont = builtins:set_cp(B),
          Conts = []
       ;  functor(Gs, ';', 2) ->
          arg(1, Gs, G1),
          arg(2, Gs, G2),
          comma_dispatch_prep(G1, B, IConts0),
          comma_dispatch_prep(G2, B, IConts1),
          cont_list_goal(IConts0, Cont0),
          cont_list_goal(IConts1, Cont1),
          Cont = ( Cont0 ; Cont1 ),
          Conts = []
       ;  functor(Gs, ->, 2) ->
          arg(1, Gs, G1),
          arg(2, Gs, G2),
          comma_dispatch_prep(G1, B, IConts1),
          comma_dispatch_prep(G2, B, IConts2),
          cont_list_goal(IConts1, Cont1),
          cont_list_goal(IConts2, Cont2),
          Cont = (Cont1 -> Cont2),
          Conts = []
       ;  Cont = Gs,
          Conts = []
       )
    ;  Cont = Gs,
       Conts = []
    ).

:- non_counted_backtracking comma_dispatch_call_list/1.

comma_dispatch_call_list([]).
comma_dispatch_call_list([G1,G2,G3,G4,G5,G6,G7,G8|Gs]) :-
    !,
    '$call'(G1),
    '$call'(G2),
    '$call'(G3),
    '$call'(G4),
    '$call'(G5),
    '$call'(G6),
    '$call'(G7),
    '$call'(G8),
    '$call_with_default_policy'(comma_dispatch_call_list(Gs)).
comma_dispatch_call_list([G1,G2,G3,G4,G5,G6,G7]) :-
    !,
    '$call'(G1),
    '$call'(G2),
    '$call'(G3),
    '$call'(G4),
    '$call'(G5),
    '$call'(G6),
    '$call'(G7).
comma_dispatch_call_list([G1,G2,G3,G4,G5,G6]) :-
    !,
    '$call'(G1),
    '$call'(G2),
    '$call'(G3),
    '$call'(G4),
    '$call'(G5),
    '$call'(G6).
comma_dispatch_call_list([G1,G2,G3,G4,G5]) :-
    !,
    '$call'(G1),
    '$call'(G2),
    '$call'(G3),
    '$call'(G4),
    '$call'(G5).
comma_dispatch_call_list([G1,G2,G3,G4]) :-
    !,
    '$call'(G1),
    '$call'(G2),
    '$call'(G3),
    '$call'(G4).
comma_dispatch_call_list([G1,G2,G3]) :-
    !,
    '$call'(G1),
    '$call'(G2),
    '$call'(G3).
comma_dispatch_call_list([G1,G2]) :-
    !,
    '$call'(G1),
    '$call'(G2).
comma_dispatch_call_list([G1]) :-
    '$call'(G1).


% univ.

:- non_counted_backtracking univ_errors/3.
univ_errors(Term, List, N) :-
    '$skip_max_list'(N, -1, 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
    ).

Term =.. List :-
    '$call_with_default_policy'(univ_errors(Term, List, N)),
    '$call_with_default_policy'(univ_worker(Term, List, N)).


:- non_counted_backtracking univ_worker/3.

univ_worker(Term, List, _) :-
    atomic(Term),
    !,
    '$call_with_default_policy'(List = [Term]).
univ_worker(Term, [Name|Args], N) :-
    var(Term),
    !,
    '$call_with_default_policy'(Arity is N-1),
    '$call_with_default_policy'(functor(Term, Name, Arity)), % Term = {var}, Name = nonvar, Arity = 0.
    '$call_with_default_policy'(get_args(Args, Term, 1, Arity)).
univ_worker(Term, List, _) :-
    '$call_with_default_policy'(functor(Term, Name, Arity)),
    '$call_with_default_policy'(get_args(Args, Term, 1, Arity)),
    '$call_with_default_policy'(List = [Name|Args]).


:- non_counted_backtracking get_args/4.

get_args(Args, _, _, 0) :-
    !,
    '$call_with_default_policy'(Args = []).
get_args([Arg], Func, N, N) :-
    !,
    '$call_with_default_policy'(arg(N, Func, Arg)).
get_args([Arg|Args], Func, I0, N) :-
    '$call_with_default_policy'(arg(I0, Func, Arg)),
    '$call_with_default_policy'(I1 is I0 + 1),
    '$call_with_default_policy'(get_args(Args, Func, I1, N)).


:- meta_predicate parse_options_list(?, 0, ?, ?, ?).

parse_options_list(Options, Selector, DefaultPairs, OptionValues, Stub) :-
    '$skip_max_list'(_, -1, 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(nonvar, Options),
       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 = [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_(ignore_ops(IgnoreOps), ignore_ops-IgnoreOps) :-
    (  nonvar(IgnoreOps),
       lists:member(IgnoreOps, [true, false])
    ;
       throw(error(domain_error(write_option, ignore_ops(IgnoreOps)), _))
    ).
parse_write_options_(quoted(Quoted), quoted-Quoted) :-
    (  nonvar(Quoted),
       lists:member(Quoted, [true, false])
    ;
       throw(error(domain_error(write_option, quoted(Quoted)), _))
    ).
parse_write_options_(numbervars(NumberVars), numbervars-NumberVars) :-
    (  nonvar(NumberVars),
       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) :-
    (  integer(MaxDepth),
       MaxDepth >= 0
    ;
       throw(error(domain_error(write_option, max_depth(MaxDepth)), _))
    ).

must_be_var_names_list(VarNames) :-
    '$skip_max_list'(_, -1, 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) :-
    current_output(Stream),
    write_term(Stream, Term, Options).

write_term(Stream, Term, Options) :-
    parse_write_options(Options, [IgnoreOps, MaxDepth, NumberVars, Quoted, VNNames], write_term/3),
    '$write_term'(Stream, Term, IgnoreOps, NumberVars, Quoted, VNNames, MaxDepth).


write(Term) :-
    current_output(Stream),
    '$write_term'(Stream, Term, false, true, false, [], 0).

write(Stream, Term) :-
    '$write_term'(Stream, Term, false, true, false, [], 0).

write_canonical(Term) :-
    current_output(Stream),
    '$write_term'(Stream, Term, true, false, true, [], 0).

write_canonical(Stream, Term) :-
    '$write_term'(Stream, Term, true, false, true, [], 0).

writeq(Term) :-
    current_output(Stream),
    '$write_term'(Stream, Term, false, true, true, [], 0).

writeq(Stream, Term) :-
    '$write_term'(Stream, Term, false, true, true, [], 0).

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) :-
    parse_read_term_options(Options, [Singletons, VariableNames, Variables], read_term/3),
    '$read_term'(Stream, Term, Singletons, Variables, VariableNames).

read_term(Term, Options) :-
    current_input(Stream),
    read_term(Stream, Term, Options).

read(Term) :-
    current_input(Stream),
    read(Stream, Term).

% term_variables.

% ensures List is either a variable or a list.
can_be_list(List, _)  :-
    var(List),
    !.
can_be_list(List, _)  :-
    '$skip_max_list'(_, -1, List, Tail),
    (  var(Tail) ->
       true
    ;  Tail == []
    ),
    !.
can_be_list(List, PI) :-
    throw(error(type_error(list, List), PI)).

term_variables(Term, Vars) :-
    can_be_list(Vars, term_variables/2),
    '$term_variables'(Term, Vars).

% exceptions.

:- meta_predicate catch(0, ?, 0).

catch(G,C,R) :-
    '$get_current_block'(Bb),
    '$call_with_default_policy'(catch(G,C,R,Bb)).

:- non_counted_backtracking catch/4.
catch(G,C,R,Bb) :-
    '$install_new_block'(NBb),
    call(G),
    '$call_with_default_policy'(end_block(Bb, NBb)).
catch(G,C,R,Bb) :-
    '$reset_block'(Bb),
    '$get_ball'(Ball),
    '$call_with_default_policy'(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) :-
    !,
    '$erase_ball',
    call(R).
handle_ball(_, _, _) :-
    '$unwind_stack'.

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'(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, ?).

findall(Template, Goal, Solutions) :-
    '$call_with_default_policy'(error:can_be(list, Solutions)),
    '$lh_length'(LhLength),
    '$call_with_default_policy'(
        catch(builtins:'$iterate_find_all'(Template, Goal, Solutions, LhLength),
              Error,
              ( builtins:truncate_lh_to(LhLength), builtins:throw(Error) ))
    ).

:- non_counted_backtracking '$iterate_find_all_diff'/5.

'$iterate_find_all_diff'(Template, Goal, _, _, LhOffset) :-
    call(Goal),
    '$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, ?, ?).

findall(Template, Goal, Solutions0, Solutions1) :-
    '$call_with_default_policy'(error:can_be(list, Solutions0)),
    '$call_with_default_policy'(error:can_be(list, Solutions1)),
    '$lh_length'(LhLength),
    '$call_with_default_policy'(
        catch(builtins:'$iterate_find_all_diff'(Template, Goal, Solutions0,
                                                Solutions1, LhLength),
              Error,
              ( builtins:truncate_lh_to(LhLength), builtins:throw(Error) ))
    ).

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).

group_by_variant([V2-S2 | Pairs], V1-S1, [S2 | Solutions], Pairs0) :-
    V1 = V2, % \+ \+ (V1 = V2), % (2) % iso_ext:variant(V1, V2), % (1)
    !,
    % V1 = V2, % (3)
    group_by_variant(Pairs, V2-S2, Solutions, Pairs0).
group_by_variant(Pairs, _, [], Pairs).

group_by_variants([V-S|Pairs], [V-Solution|Solutions]) :-
    group_by_variant([V-S|Pairs], V-S, Solution, Pairs0),
    group_by_variants(Pairs0, Solutions).
group_by_variants([], []).

iterate_variants([V-Solution|GroupSolutions], V, Solution) :-
    (  GroupSolutions == [] -> !
    ;  true
    ).
iterate_variants([_|GroupSolutions], Ws, Solution) :-
    iterate_variants(GroupSolutions, Ws, Solution).


rightmost_power(Term, FinalTerm, Xs) :-
    (  Term = X ^ Y
    -> (  var(Y) -> FinalTerm = Y, Xs = [X]
       ;  Xs = [X | Xss], rightmost_power(Y, FinalTerm, Xss)
       )
    ;  Term = M : X ^ Y
    -> (  var(Y) -> FinalTerm = M:Y, Xs = [X]
       ;  Xs = [X | Xss], rightmost_power(M:Y, FinalTerm, Xss)
       )
    ;  Xs = [], FinalTerm = Term
    ).


findall_with_existential(Template, Goal, PairedSolutions, Witnesses0, Witnesses) :-
    (  nonvar(Goal),
       (  Goal = _ ^ _
       ;  Goal = _ : (_ ^ _)
       )  ->
       rightmost_power(Goal, Goal1, ExistentialVars0),
       term_variables(ExistentialVars0, ExistentialVars),
       sort(Witnesses0, Witnesses1),
       sort(ExistentialVars, ExistentialVars1),
       set_difference(Witnesses1, ExistentialVars1, Witnesses),
       findall(Witnesses-Template, Goal1, PairedSolutions)
    ;  Witnesses = Witnesses0,
       findall(Witnesses-Template, Goal, PairedSolutions)
    ).


:- meta_predicate bagof(?, 0, ?).

bagof(Template, Goal, Solution) :-
    error:can_be(list, Solution),
    term_variables(Template, TemplateVars0),
    term_variables(Goal, GoalVars0),
    sort(TemplateVars0, TemplateVars),
    sort(GoalVars0, GoalVars),
    set_difference(GoalVars, TemplateVars, Witnesses0),
    findall_with_existential(Template, Goal, PairedSolutions0, Witnesses0, Witnesses),
    keysort(PairedSolutions0, PairedSolutions),
    group_by_variants(PairedSolutions, GroupedSolutions),
    iterate_variants(GroupedSolutions, Witnesses, Solution).

iterate_variants_and_sort([V-Solution0|GroupSolutions], V, Solution) :-
    sort(Solution0, Solution),
    (  GroupSolutions == [] -> !
    ;  true
    ).
iterate_variants_and_sort([_|GroupSolutions], Ws, Solution) :-
    iterate_variants_and_sort(GroupSolutions, Ws, Solution).


:- meta_predicate setof(?, 0, ?).

setof(Template, Goal, Solution) :-
    error:can_be(list, Solution),
    term_variables(Template, TemplateVars0),
    term_variables(Goal, GoalVars0),
    sort(TemplateVars0, TemplateVars),
    sort(GoalVars0, GoalVars),
    set_difference(GoalVars, TemplateVars, Witnesses0),
    findall_with_existential(Template, Goal, PairedSolutions0, Witnesses0, Witnesses),
    keysort(PairedSolutions0, PairedSolutions),
    group_by_variants(PairedSolutions, GroupedSolutions),
    iterate_variants_and_sort(GroupedSolutions, Witnesses, Solution).

% Clause retrieval and information.

'$clause_body_is_valid'(B) :-
    (  var(B) -> true
    ;  functor(B, Name, _) ->
       (  atom(Name), Name \== '.' -> true
       ;  throw(error(type_error(callable, B), clause/2))
       )
    ;  throw(error(type_error(callable, B), clause/2))
    ).

'$module_clause'(H, B, Module) :-
    (  var(H) ->
       throw(error(instantiation_error, clause/2))
    ;  callable(H), functor(H, Name, Arity) ->
       (  '$no_such_predicate'(Module, H) ->
          '$fail'
       ;  '$head_is_dynamic'(Module, H) ->
          '$clause_body_is_valid'(B),
          Module:'$clause'(H, B)
       ;  throw(error(permission_error(access, private_procedure, Name/Arity),
                      clause/2))
       )
    ;  throw(error(type_error(callable, H), clause/2))
    ).


clause(H, B) :-
    (  var(H) ->
       throw(error(instantiation_error, clause/2))
    ;  callable(H), functor(H, Name, Arity) ->
       (  Name == (:),
          Arity =:= 2 ->
          arg(1, H, Module),
          arg(2, H, F),
          '$module_clause'(F, B, Module)
       ;  '$no_such_predicate'(user, H) ->
          '$fail'
       ;  '$head_is_dynamic'(user, H) ->
          '$clause_body_is_valid'(B),
          '$clause'(H, B)
       ;  throw(error(permission_error(access, private_procedure, Name/Arity),
                      clause/2))
       )
    ;  throw(error(type_error(callable, H), clause/2))
    ).

call_asserta(Head, Body, Name, Arity, Module) :-
    '$clause_body_is_valid'(Body),
    functor(_, Name, Arity),
    '$asserta'(Head, Body, Name, Arity, Module).

module_asserta_clause(Head, Body, Module) :-
    (  var(Head) ->
       throw(error(instantiation_error, asserta/1))
    ;  callable(Head), functor(Head, Name, Arity) ->
       (  '$head_is_dynamic'(Module, Head) ->
          call_asserta(Head, Body, Name, Arity, Module)
       ;  '$no_such_predicate'(Module, Head) ->
          call_asserta(Head, Body, Name, Arity, Module)
       ;  throw(error(permission_error(modify, static_procedure, Name/Arity), asserta/1))
       )
    ;  throw(error(type_error(callable, Head), asserta/1))
    ).

asserta_clause(Head, Body) :-
    (  var(Head) -> throw(error(instantiation_error, asserta/1))
    ;  callable(Head), functor(Head, Name, Arity) ->
       ( Name == (:),
         Arity =:= 2 ->
         arg(1, Head, Module),
         arg(2, Head, HeadAndBody),
         (  HeadAndBody = (F :- Body1) ->
            true
         ;  F = HeadAndBody,
            Body1 = true
         ),
         module_asserta_clause(F, Body1, Module)
       ; '$head_is_dynamic'(user, Head) ->
          call_asserta(Head, Body, Name, Arity, user)
       ; '$no_such_predicate'(user, Head) ->
          call_asserta(Head, Body, Name, Arity, user)
       ;  throw(error(permission_error(modify, static_procedure, Name/Arity), asserta/1))
       )
    ;  throw(error(type_error(callable, Head), asserta/1))
    ).

:- meta_predicate asserta(0).

asserta(Clause0) :-
    loader:strip_module(Clause0, Module, Clause),
    (  Clause \= (_ :- _) ->
       Head = Clause,
       Body = true,
       module_asserta_clause(Head, Body, Module)
    ;  Clause = (Head :- Body) ->
       module_asserta_clause(Head, Body, Module)
    ).

module_assertz_clause(Head, Body, Module) :-
    (  var(Head) ->
       throw(error(instantiation_error, assertz/1))
    ;  callable(Head), functor(Head, Name, Arity) ->
       (  '$head_is_dynamic'(Module, Head) ->
          call_assertz(Head, Body, Name, Arity, Module)
       ;  '$no_such_predicate'(Module, Head) ->
          call_assertz(Head, Body, Name, Arity, Module)
       ;  throw(error(permission_error(modify, static_procedure, Name/Arity),
                      assertz/1))
       )
    ;  throw(error(type_error(callable, Head), assertz/1))
    ).


call_assertz(Head, Body, Name, Arity, Module) :-
    '$clause_body_is_valid'(Body),
    functor(_, Name, Arity),
    '$assertz'(Head, Body, Name, Arity, Module).

assertz_clause(Head, Body) :-
    (  var(Head) ->
       throw(error(instantiation_error, assertz/1))
    ;  callable(Head), functor(Head, Name, Arity) ->
       (  Name == (:),
          Arity =:= 2 ->
          arg(1, Head, Module),
          arg(2, Head, HeadAndBody),
          (  HeadAndBody = (F :- Body1) ->
             true
          ;  F = HeadAndBody,
             Body1 = true
          ),
          module_assertz_clause(F, Body1, Module)
       ;  '$head_is_dynamic'(user, Head) ->
          call_assertz(Head, Body, Name, Arity, user)
       ;  '$no_such_predicate'(user, Head) ->
          call_assertz(Head, Body, Name, Arity, user)
       ;  throw(error(permission_error(modify, static_procedure, Name/Arity),
                      assertz/1))
       )
    ;  throw(error(type_error(callable, Head), assertz/1))
    ).

:- meta_predicate assertz(0).

assertz(Clause0) :-
    loader:strip_module(Clause0, Module, Clause),
    (  Clause \= (_ :- _) ->
       Head = Clause,
       Body = true,
       module_assertz_clause(Head, Body, Module)
    ;  Clause = (Head :- Body) ->
       module_assertz_clause(Head, Body, Module)
    ).


module_retract_clauses([Clause|Clauses0], Head, Body, Name, Arity, Module) :-
    functor(VarHead, Name, Arity),
    findall((VarHead :- VarBody), Module:'$clause'(VarHead, VarBody), Clauses1),
    (  first_match_index(Clauses1, (Head :- Body), 0, N) ->
       '$retract_clause'(Name, Arity, N, Module)
    ;  Clause = (Head :- Body)
    ),
    (  Clauses0 == [] -> !
    ;  true
    ).

module_retract_clauses([_|Clauses0], Head, Body, Name, Arity, Module) :-
    module_retract_clauses(Clauses0, Head, Body, Name, Arity, Module).

call_module_retract(Head, Body, Name, Arity, Module) :-
    findall((Head :- Body), Module:'$clause'(Head, Body), Clauses),
    module_retract_clauses(Clauses, Head, Body, Name, Arity, Module).

retract_module_clause(Head, Body, Module) :-
    (  var(Head) ->
       throw(error(instantiation_error, retract/1))
    ;  callable(Head), functor(Head, Name, Arity) ->
       (  '$no_such_predicate'(Module, Head) ->
          '$fail'
       ;  '$head_is_dynamic'(Module, Head) ->
          (  Module == user ->
             call_retract(Head, Body, Name, Arity)
          ;  call_module_retract(Head, Body, Name, Arity, Module)
          )
       ;  throw(error(permission_error(modify, static_procedure, Name/Arity), retract/1))
       )
    ;  throw(error(type_error(callable, Head), retract/1))
    ).


first_match_index([Clause | _], Clause, N, N) :-
    !.
first_match_index([_ | Clauses], Clause, N0, N) :-
    N1 is N0 + 1,
    first_match_index(Clauses, Clause, N1, N).

retract_clauses([Clause | Clauses0], Head, Body, Name, Arity) :-
    functor(VarHead, Name, Arity),
    findall((VarHead :- VarBody), builtins:'$clause'(VarHead, VarBody), Clauses1),
    (  first_match_index(Clauses1, (Head :- Body), 0, N) ->
       '$retract_clause'(Name, Arity, N, user)
    ;  Clause = (Head :- Body)
    ),
    (  Clauses0 == [] -> !
    ;  true
    ).

retract_clauses([_ | Clauses0], Head, Body, Name, Arity) :-
    retract_clauses(Clauses0, Head, Body, Name, Arity).

call_retract(Head, Body, Name, Arity) :-
    findall((Head :- Body), builtins:'$clause'(Head, Body), Clauses),
    retract_clauses(Clauses, Head, Body, Name, Arity).

retract_clause(Head, Body) :-
    (  var(Head) ->
       throw(error(instantiation_error, retract/1))
    ;  callable(Head), functor(Head, Name, Arity) ->
       (  Name == (:),
          Arity =:= 2 ->
          arg(1, Head, Module),
          arg(2, Head, Head1),
          retract_module_clause(Head1, Body, Module)
       ;  '$no_such_predicate'(user, Head) ->
          '$fail'
       ;  '$head_is_dynamic'(user, Head) ->
          call_retract(Head, Body, Name, Arity)
       ;  throw(error(permission_error(modify, static_procedure, Name/Arity), retract/1))
       )
    ;  throw(error(type_error(callable, Head), retract/1))
    ).

:- meta_predicate retract(0).

retract(Clause0) :-
    loader:strip_module(Clause0, Module, Clause),
    (  Clause \= (_ :- _) ->
       Head = Clause,
       Body = true,
       retract_module_clause(Head, Body, Module)
    ;  Clause = (Head :- Body) ->
       retract_module_clause(Head, Body, Module)
    ).


:- meta_predicate retractall(0).

retractall(Head) :-
   retract_clause(Head, _),
   false.
retractall(_).


module_abolish(Pred, Module) :-
    (  var(Pred) ->
       throw(error(instantiation_error, abolish/1))
    ;  Pred = Name/Arity ->
       (  var(Name)  ->
          throw(error(instantiation_error, abolish/1))
       ;  var(Arity) ->
          throw(error(instantiation_error, abolish/1))
       ;  integer(Arity) ->
          (\+ atom(Name) ->
             throw(error(type_error(atom, Name), abolish/1))
          ;  Arity < 0 ->
             throw(error(domain_error(not_less_than_zero, Arity), abolish/1))
          ;  current_prolog_flag(max_arity, N), Arity > N ->
             throw(error(representation_error(max_arity), abolish/1))
          ;  functor(Head, Name, Arity) ->
             (  '$head_is_dynamic'(Module, Head) ->
                '$abolish_clause'(Module, Name, Arity)
             ;  '$no_such_predicate'(Module, Head) ->
                true
             ;  throw(error(permission_error(modify, static_procedure, Pred), abolish/1))
             )
          )
       ;  throw(error(type_error(integer, Arity), abolish/1))
       )
    ;  throw(error(type_error(predicate_indicator, Module:Pred), abolish/1))
    ).


:- meta_predicate abolish(0).

abolish(Pred) :-
    (  var(Pred) ->
       throw(error(instantiation_error, abolish/1))
    ;  Pred = Module:InnerPred ->
       module_abolish(InnerPred, Module)
    ;  Pred = Name/Arity ->
       (  var(Name)  ->
          throw(error(instantiation_error, abolish/1))
       ;  var(Arity) ->
          throw(error(instantiation_error, abolish/1))
       ;  integer(Arity) ->
          (  \+ atom(Name) ->
             throw(error(type_error(atom, Name), abolish/1))
          ;  Arity < 0 ->
             throw(error(domain_error(not_less_than_zero, Arity), abolish/1))
          ;  current_prolog_flag(max_arity, N), Arity > N ->
             throw(error(representation_error(max_arity), abolish/1))
          ;  functor(Head, Name, Arity) ->
             (  '$head_is_dynamic'(user, Head) ->
                '$abolish_clause'(user, Name, Arity)
             ;  '$no_such_predicate'(user, Head) ->
                true
             ;  throw(error(permission_error(modify, static_procedure, Pred), abolish/1))
             )
          )
       ;  throw(error(type_error(integer, Arity), abolish/1))
       )
    ;  throw(error(type_error(predicate_indicator, Pred), abolish/1))
    ).

'$iterate_db_refs'(Name, Arity, Name/Arity). % :-
%   '$lookup_db_ref'(Ref, Name, Arity).
'$iterate_db_refs'(RName, RArity, Name/Arity) :-
    '$get_next_db_ref'(RName, RArity, RRName, RRArity),
    '$iterate_db_refs'(RRName, RRArity, Name/Arity).

current_predicate(Pred) :-
    (  var(Pred) ->
       '$get_next_db_ref'(RN, RA, _, _),
       '$iterate_db_refs'(RN, RA, Pred)
    ;  Pred \= _/_ ->
       throw(error(type_error(predicate_indicator, Pred), current_predicate/1))
    ;  Pred = Name/Arity,
       (  nonvar(Name), \+ atom(Name)
       ;  nonvar(Arity), \+ integer(Arity)
       ;  integer(Arity), Arity < 0
       ) ->
       throw(error(type_error(predicate_indicator, Pred), current_predicate/1))
    ;  '$get_next_db_ref'(RN, RA, _, _),
       '$iterate_db_refs'(RN, RA, Pred)
    ).

'$iterate_op_db_refs'(RPriority, RSpec, ROp, _, RPriority, RSpec, ROp).
'$iterate_op_db_refs'(RPriority, RSpec, ROp, OssifiedOpDir, Priority, Spec, Op) :-
    '$get_next_op_db_ref'(RPriority, RSpec, ROp, OssifiedOpDir, RRPriority, RRSpec, RROp),
    '$iterate_op_db_refs'(RRPriority, RRSpec, RROp, OssifiedOpDir, Priority, Spec, Op).

can_be_op_priority(Priority) :- var(Priority).
can_be_op_priority(Priority) :- op_priority(Priority).

can_be_op_specifier(Spec) :- var(Spec).
can_be_op_specifier(Spec) :- op_specifier(Spec).

current_op(Priority, Spec, Op) :-
    (  can_be_op_priority(Priority),
       can_be_op_specifier(Spec),
       error:can_be(atom, Op) ->
       '$get_next_op_db_ref'(RPriority, RSpec, ROp, OssifiedOpDir, _, _, Op),
       '$iterate_op_db_refs'(RPriority, RSpec, ROp, OssifiedOpDir, Priority, Spec, Op)
    ).

list_of_op_atoms(Var) :-
    var(Var), throw(error(instantiation_error, op/3)). % 8.14.3.3 c)
list_of_op_atoms([Atom|Atoms]) :-
    ( valid_op(Atom) -> list_of_op_atoms(Atoms) % 8.14.3.3 k).
    ; var(Atom) -> throw(error(instantiation_error, op/3)) % 8.14.3.3 c)
    ; throw(error(type_error(atom, Atom), op/3)) % 8.14.3.3 g)
    ).
list_of_op_atoms([]).

op_priority(Priority) :-
    integer(Priority), !,
    (  ( Priority < 0 ; Priority > 1200 ) ->
       throw(error(domain_error(operator_priority, Priority), op/3)) % 8.14.3.3 h)
    ;  true
    ).

op_priority(Priority) :-
    throw(error(type_error(integer, Priority), op/3)). % 8.14.3.3 d)

op_specifier(OpSpec) :-
    atom(OpSpec),
    (  lists:member(OpSpec, [yfx, xfy, xfx, yf, fy, xf, fx]), !
    ;  throw(error(domain_error(operator_specifier, OpSpec), op/3)) % 8.14.3.3 i)
    ).

op_specifier(OpSpec) :-
    throw(error(type_error(atom, OpSpec), op/3)).

valid_op(Op) :-
    atom(Op),
    (  Op == (',') ->
       throw(error(permission_error(modify, operator, (',')), op/3)) % 8.14.3.3 j), k).
    ;  Op == {} ->
       throw(error(permission_error(create, operator, {}), op/3))
    ;  Op == [] ->
       throw(error(permission_error(create, operator, []), op/3))
    ;  true
    ).

op_(Priority, OpSpec, Op) :-
    '$op'(Priority, OpSpec, Op).

op(Priority, OpSpec, Op) :-
    (  var(Priority) ->
       throw(error(instantiation_error, op/3)) % 8.14.3.3 a)
    ;  var(OpSpec)   ->
       throw(error(instantiation_error, op/3)) % 8.14.3.3 b)
    ;  var(Op)       ->
       throw(error(instantiation_error, op/3)) % 8.14.3.3 c)
    ;  Op == '|'     ->
       (  op_priority(Priority),
          op_specifier(OpSpec),
          lists:member(OpSpec, [xfx, xfy, yfx]),
          ( Priority >= 1001 ; Priority == 0 )
       -> '$op'(Priority, OpSpec, Op)
       ;  throw(error(permission_error(create, operator, (|)), op/3))) % www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_testing#72
    ;  valid_op(Op), op_priority(Priority), op_specifier(OpSpec) ->
       '$op'(Priority, OpSpec, Op)
    ;  list_of_op_atoms(Op), op_priority(Priority), op_specifier(OpSpec) ->
       lists:maplist(builtins:op_(Priority, OpSpec), Op),
       !
    ;  throw(error(type_error(list, Op), op/3)) % 8.14.3.3 f)
    ).


halt :- halt(0).

halt(N) :-
        must_be_number(N, halt/1),
        (   -2^31 =< N, N =< 2^31 - 1 ->
            '$halt'(N)
        ;   throw(error(domain_error(exit_code, N), halt/1))
        ).

atom_length(Atom, Length) :-
    (  var(Atom)  ->
       throw(error(instantiation_error, atom_length/2)) % 8.16.1.3 a)
    ;  atom(Atom) ->
       (  var(Length) ->
          '$atom_length'(Atom, Length)
       ;  integer(Length), Length >= 0 ->
          '$atom_length'(Atom, Length)
       ;  integer(Length) ->
          throw(error(domain_error(not_less_than_zero, Length), atom_length/2))
       % 8.16.1.3 d)
       ;  throw(error(type_error(integer, Length), atom_length/2)) % 8.16.1.3 c)
       )
    ;  throw(error(type_error(atom, Atom), atom_length/2)) % 8.16.1.3 b)
    ).

atom_chars(Atom, List) :-
    '$skip_max_list'(_, -1, List, Tail),
    (  ( Tail == [] ; var(Tail) ) ->
       true
    ;  throw(error(type_error(list, List), atom_chars/2))
    ),
    (  var(Atom) ->
       (  var(Tail) ->
          throw(error(instantiation_error, atom_chars/2))
       ;  ground(List) ->
          '$atom_chars'(Atom, List)
       ;  throw(error(instantiation_error, atom_chars/2))
       )
    ;  atom(Atom) ->
       '$atom_chars'(Atom, List)
    ;  throw(error(type_error(atom, Atom), atom_chars/2))
    ).

atom_codes(Atom, List) :-
    '$skip_max_list'(_, -1, List, Tail),
    (  ( Tail == [] ; var(Tail) ) ->
       true
    ;  throw(error(type_error(list, List), atom_codes/2))
    ),
    (  var(Atom) ->
       (  var(Tail) ->
          throw(error(instantiation_error, atom_codes/2))
       ;  ground(List), Tail == [] ->
          '$atom_codes'(Atom, List)
       ;  throw(error(instantiation_error, atom_codes/2))
       )
    ;  atom(Atom) ->
       '$atom_codes'(Atom, List)
    ;  throw(error(type_error(atom, Atom), atom_codes/2))
    ).

atom_concat(Atom_1, Atom_2, Atom_12) :-
    error:can_be(atom, Atom_1),
    error:can_be(atom, Atom_2),
    error:can_be(atom, Atom_12),
    (  var(Atom_1) ->
       (  var(Atom_12) ->
          throw(error(instantiation_error, atom_concat/3))
       ;  atom_chars(Atom_12, Atom_12_Chars),
          lists:append(BeforeChars, AfterChars, Atom_12_Chars),
          atom_chars(Atom_1, BeforeChars),
          atom_chars(Atom_2, AfterChars)
       )
    ;  var(Atom_2) ->
       (  var(Atom_12) -> throw(error(instantiation_error, atom_concat/3))
       ;  atom_chars(Atom_1, Atom_1_Chars),
          atom_chars(Atom_12, Atom_12_Chars),
          lists:append(Atom_1_Chars, Atom_2_Chars, Atom_12_Chars),
          atom_chars(Atom_2, Atom_2_Chars)
       )
    ;  atom_chars(Atom_1, Atom_1_Chars),
       atom_chars(Atom_2, Atom_2_Chars),
       lists:append(Atom_1_Chars, Atom_2_Chars, Atom_12_Chars),
       atom_chars(Atom_12, Atom_12_Chars)
    ).

sub_atom(Atom, Before, Length, After, Sub_atom) :-
    error:must_be(atom, Atom),
    error:can_be(atom, Sub_atom),
    error:can_be(integer, Before),
    error:can_be(integer, Length),
    error:can_be(integer, After),
    (  integer(Before), Before < 0 ->
       throw(error(domain_error(not_less_than_zero, Before), sub_atom/5))
    ;  integer(Length), Length < 0 ->
       throw(error(domain_error(not_less_than_zero, Length), sub_atom/5))
    ;  integer(After), After < 0 ->
       throw(error(domain_error(not_less_than_zero, After), sub_atom/5))
    ;  atom_chars(Atom, AtomChars),
       lists:append(BeforeChars, LengthAndAfterChars, AtomChars),
       lists:append(LengthChars, AfterChars, LengthAndAfterChars),
       '$skip_max_list'(Before, -1, BeforeChars, []),
       '$skip_max_list'(Length, -1, LengthChars, []),
       '$skip_max_list'(After, -1, AfterChars, []),
       atom_chars(Sub_atom, LengthChars)
    ).

char_code(Char, Code) :-
    (  var(Char) ->
       (  var(Code) ->
          throw(error(instantiation_error, char_code/2))
       ;  integer(Code) ->
          '$char_code'(Char, Code)
       ;  throw(error(type_error(integer, Code), char_code/2))
       )
    ;  \+ atom(Char) ->
       throw(error(type_error(character, Char), char_code/2))
    ;  atom_length(Char, 1) ->
       (  var(Code) ->
          '$char_code'(Char, Code)
       ;  integer(Code) ->
          '$char_code'(Char, Code)
       ;  throw(error(type_error(integer, Code), char_code/2))
       )
    ;  throw(error(type_error(character, Char), char_code/2))
    ).

get_char(C) :-
    error:can_be(character, C),
    current_input(S),
    '$get_char'(S, C).

get_char(S, C) :-
    error:can_be(character, C),
    '$get_char'(S, C).

can_be_number(N, PI) :-
    (  var(N) -> true
    ;  must_be_number(N, PI)
    ).

must_be_number(N, _) :-
    (  integer(N)
    ;  float(N)
    ),
    !.
must_be_number(N, PI) :-
    (  nonvar(N) ->
       throw(error(type_error(number, N), PI))
    ;  throw(error(instantiation_error, PI))
    ).

can_be_chars_or_vars(Cs, _) :- var(Cs), !.
can_be_chars_or_vars(Cs, PI) :- chars_or_vars(Cs, PI).

chars_or_vars([], _).
chars_or_vars([C|Cs], PI) :-
    (  nonvar(C) ->
       (  catch(builtins:atom_length(C, 1), _, false) ->
          (  nonvar(Cs) ->
             chars_or_vars(Cs, PI)
          ;  false
          )
       ;  throw(error(type_error(character, C), PI))
       )
    ;  chars_or_vars(Cs, PI)
    ).

can_be_codes_or_vars(Cs, _) :- var(Cs), !.
can_be_codes_or_vars(Cs, PI) :- codes_or_vars(Cs, PI).

codes_or_vars([], _).
codes_or_vars([C|Cs], PI) :-
    (  nonvar(C) ->
       (  catch(builtins:char_code(_, C), _, false) ->
          (  nonvar(Cs) -> codes_or_vars(Cs, PI)
          ;  false
          )
       ;  integer(C) ->
          throw(error(representation_error(character_code), PI))
       ;  throw(error(type_error(integer, C), PI))
       )
    ;  codes_or_vars(Cs, PI)
    ).

number_chars(N, Chs) :-
   (  ground(Chs)
   -> can_be_number(N, number_chars/2),
      can_be_list(Chs, number_chars/2),
      '$chars_to_number'(Chs, Nx),
      Nx = N
   ;  must_be_number(N, number_chars/2),
      (  var(Chs) -> true
      ;  can_be_list(Chs, number_chars/2)
      ,  chars_or_vars(Chs, number_chars/2)
      ),
      '$number_to_chars'(N, Chsx),
      Chsx = Chs
    ).

number_codes(N, Chs) :-
   (  ground(Chs)
   -> can_be_number(N, number_codes/2),
      can_be_list(Chs, number_codes/2),
      '$codes_to_number'(Chs, Nx),
      Nx = N
   ;  must_be_number(N, number_codes/2),
      (  var(Chs) -> true
      ;  can_be_list(Chs, number_codes/2)
      ,  codes_or_vars(Chs, number_codes/2)
      ),
      '$number_to_codes'(N, Chsx),
      Chsx = Chs
    ).

subsumes_term(General, Specific) :-
   \+ \+ (
      term_variables(Specific, SVs1),
      unify_with_occurs_check(General, Specific),
      term_variables(SVs1, SVs2),
      SVs1 == SVs2
   ).

unify_with_occurs_check(X, Y) :- '$unify_with_occurs_check'(X, Y).

current_input(S) :- '$current_input'(S).

current_output(S) :- '$current_output'(S).

set_input(S) :-
    (  var(S) ->
       throw(error(instantiation_error, set_input/1))
    ;  '$set_input'(S)
    ).

set_output(S) :-
    (  var(S) ->
       throw(error(instantiation_error, set_output/1))
    ;  '$set_output'(S)
    ).


parse_stream_options(Options, OptionValues, Stub) :-
    DefaultOptions = [alias-[], eof_action-eof_code, reposition-false, type-text],
    parse_options_list(Options, builtins:parse_stream_options_, DefaultOptions, OptionValues, Stub).


parse_stream_options_(type(Type), type-Type) :-
    (  var(Type) ->
       throw(error(instantiation_error, open/4)) % 8.1.3 7)
    ;
       lists:member(Type, [text, binary]) -> true
    ;
       throw(error(domain_error(stream_option, type(Type)), _))
    ).
parse_stream_options_(reposition(Bool), reposition-Bool) :-
    (  nonvar(Bool), lists:member(Bool, [true, false]), !, true
    ;
       throw(error(domain_error(stream_option, reposition(Bool)), _))
    ).
parse_stream_options_(alias(A), alias-A) :-
    (  var(A) ->
       throw(error(instantiation_error, open/4)) % 8.1.3 7)
    ;
       atom(A), A \== [] -> true
    ;
       throw(error(domain_error(stream_option, alias(A)), _))
    ).
parse_stream_options_(eof_action(Action), eof_action-Action) :-
    (  nonvar(Action), lists:member(Action, [eof_code, error, reset]), !, true
    ;
       throw(error(domain_error(stream_option, eof_action(Action)), _))
    ).
parse_stream_options_(E, _) :-
    throw(error(domain_error(stream_option, E), _)). % 8.11.5.3i)


open(SourceSink, Mode, Stream) :-
    open(SourceSink, Mode, Stream, []).

open(SourceSink, Mode, Stream, StreamOptions) :-
    (  var(SourceSink) ->
       throw(error(instantiation_error, open/4)) % 8.11.5.3a)
    ;  var(Mode) ->
       throw(error(instantiation_error, open/4)) % 8.11.5.3b)
    ;  \+ atom(Mode) ->
       throw(error(type_error(atom, Mode), open/4)) % 8.11.5.3d)
    ;  nonvar(Stream) ->
       throw(error(uninstantiation_error(Stream), open/4)) % 8.11.5.3f)
    ;
       parse_stream_options(StreamOptions, [Alias, EOFAction, Reposition, Type], open/4),
       (   SourceSink = stream(S0) ->
           '$set_stream_options'(S0, Alias, EOFAction, Reposition, Type),
           Stream = S0
       ;   (
                atom(SourceSink) ->
                atom_chars(SourceSink, SourceSinkString)
           ;    SourceSink = SourceSinkString
           ), '$open'(SourceSinkString, Mode, Stream, Alias, EOFAction, Reposition, Type)
       )
    ).


parse_close_options(Options, OptionValues, Stub) :-
    DefaultOptions = [force-false],
    parse_options_list(Options, builtins:parse_close_options_, DefaultOptions, OptionValues, Stub).

parse_close_options_(force(Force), force-Force) :-
    (  nonvar(Force), lists:member(Force, [true, false]), !
    ;
       throw(error(domain_error(close_option, force(Force)), _))
    ).
parse_close_options_(E, _) :-
    throw(error(domain_error(close_option, E), _)).


close(Stream, CloseOptions) :-
    parse_close_options(CloseOptions, [Force], close/2),
    '$close'(Stream, CloseOptions).

close(Stream) :-
    '$close'(Stream, []).


flush_output(S) :-
    '$flush_output'(S).

flush_output :-
    current_output(S),
    '$flush_output'(S).


get_byte(S, B) :-
    '$get_byte'(S, B).

get_byte(B) :-
    current_input(S),
    '$get_byte'(S, B).


put_char(C) :-
    current_output(S),
    '$put_char'(S, C).

put_char(S, C) :-
    '$put_char'(S, C).


put_byte(C) :-
    current_output(S),
    '$put_byte'(S, C).

put_byte(S, C) :-
    '$put_byte'(S, C).


put_code(C) :-
    current_output(S),
    '$put_code'(S, C).

put_code(S, C) :-
    '$put_code'(S, C).


get_code(C) :-
    current_input(S),
    '$get_code'(S, C).

get_code(S, C) :-
    '$get_code'(S, C).


peek_byte(S, B) :-
    '$peek_byte'(S, B).

peek_byte(B) :-
    current_input(S),
    '$peek_byte'(S, B).


peek_code(C) :-
    current_input(S),
    '$peek_code'(S, C).

peek_code(S, C) :-
    '$peek_code'(S, C).


peek_char(C) :-
    current_input(S),
    '$peek_char'(S, C).

peek_char(S, C) :-
    '$peek_char'(S, C).


is_stream_position(position_and_lines_read(P, L)) :-
    ( var(P) ; integer(P), P >= 0 ),
    ( var(L) ; integer(L), L >= 0 ),
    !.

check_stream_property(D, direction, D) :-
    ( var(D) -> true ; lists:member(D, [input, output, input_output]), ! ).
check_stream_property(file_name(F), file_name, F) :-
    ( var(F) -> true ; atom(F) ).
check_stream_property(mode(M), mode, M) :-
    ( var(M) -> true ; lists:member(M, [read, write, append]) ).
check_stream_property(alias(A), alias, A) :-
    ( var(A) -> true ; atom(A) ).
check_stream_property(position(P), position, P) :-
    ( var(P) -> true ; is_stream_position(P)).
check_stream_property(end_of_stream(E), end_of_stream, E) :-
    ( var(E) -> true ; lists:member(E, [not, at, past]) ).
check_stream_property(eof_action(A), eof_action, A) :-
    ( var(A) -> true ; lists:member(A, [error, eof_code, reset]) ).
check_stream_property(reposition(B), reposition, B) :-
    ( var(B) -> true ; lists:member(B, [true, false]) ).
check_stream_property(type(T), type, T) :-
    ( var(T) -> true ; lists:member(T, [text, binary]) ).


stream_iter_(S, S).
stream_iter_(S, S1) :-
    '$next_stream'(S, S0),
    stream_iter_(S0, S1).

stream_iter(S) :-
    (  nonvar(S) ->
       true
    ;  '$first_stream'(S0),
       stream_iter_(S0, S)
    ).


stream_property(S, P) :-
    (  nonvar(P), \+ check_stream_property(P, _, _) ->
       throw(error(domain_error(stream_property, P), stream_property/2))
    ;  stream_iter(S),
       check_stream_property(P, PropertyName, PropertyValue),
       '$stream_property'(S, PropertyName, PropertyValue)
    ).


at_end_of_stream(S_or_a) :-
    (  var(S_or_a) ->
       throw(error(instantiation_error, at_end_of_stream/1))
    ;  atom(S_or_a) ->
       stream_property(S, alias(S_or_a))
    ;  S = S_or_a
    ),
    stream_property(S, end_of_stream(E)),
    ( E = at -> true ; E = past ).

at_end_of_stream :-
    current_input(S),
    stream_property(S, end_of_stream(E)),
    !,
    ( E = at ; E = past ).


set_stream_position(S_or_a, Position) :-
    (  var(Position) ->
       throw(error(instantiation_error, set_stream_position/2))
    ;  Position = position_and_lines_read(P, _),
       is_stream_position(Position) ->
       '$set_stream_position'(S_or_a, P)
    ;  throw(error(domain_error(stream_position, Position), set_stream_position/2))
    ).

callable(X) :-
    (  nonvar(X), functor(X, F, _), atom(F) ->
       true
    ;  false
    ).

nl :-
    current_output(Stream),
    nl(Stream).

nl(Stream) :-
    put_char(Stream, '\n').