/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  1985-2025, University of Amsterdam
			      VU University Amsterdam
			      CWI, Amsterdam
			      SWI-Prolog Solutions b.v.
    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.
*/

/*
Consult, derivates and basic things.   This  module  is  loaded  by  the
C-written  bootstrap  compiler.

The $:- directive  is  executed  by  the  bootstrap  compiler,  but  not
inserted  in  the  intermediate  code  file.   Used  to print diagnostic
messages and start the Prolog defined compiler for  the  remaining  boot
modules.

If you want  to  debug  this  module,  put  a  '$:-'(trace).   directive
somewhere.   The  tracer will work properly under boot compilation as it
will use the C defined write predicate  to  print  goals  and  does  not
attempt to call the Prolog defined trace interceptor.
*/

		/********************************
		*    LOAD INTO MODULE SYSTEM    *
		********************************/

:- '$set_source_module'(system).

'$boot_message'(_Format, _Args) :-
    current_prolog_flag(verbose, silent),
    !.
'$boot_message'(Format, Args) :-
    format(Format, Args),
    !.

'$:-'('$boot_message'('Loading boot file ...~n', [])).


%!  memberchk(?E, ?List) is semidet.
%
%   Semantically equivalent to once(member(E,List)).   Implemented in C.
%   If List is partial though we need to   do  the work in Prolog to get
%   the proper constraint behavior. Needs  to   be  defined early as the
%   boot code uses it.

memberchk(E, List) :-
    '$memberchk'(E, List, Tail),
    (   nonvar(Tail)
    ->  true
    ;   Tail = [_|_],
	memberchk(E, Tail)
    ).

		/********************************
		*          DIRECTIVES           *
		*********************************/

:- meta_predicate
    dynamic(:),
    multifile(:),
    public(:),
    module_transparent(:),
    discontiguous(:),
    volatile(:),
    thread_local(:),
    noprofile(:),
    non_terminal(:),
    det(:),
    '$clausable'(:),
    '$iso'(:),
    '$hide'(:),
    '$notransact'(:).

%!  dynamic(+Spec) is det.
%!  multifile(+Spec) is det.
%!  module_transparent(+Spec) is det.
%!  discontiguous(+Spec) is det.
%!  volatile(+Spec) is det.
%!  thread_local(+Spec) is det.
%!  noprofile(+Spec) is det.
%!  public(+Spec) is det.
%!  non_terminal(+Spec) is det.
%
%   Predicate versions of standard  directives   that  set predicate
%   attributes. These predicates bail out with an error on the first
%   failure (typically permission errors).

%!  '$iso'(+Spec) is det.
%
%   Set the ISO  flag.  This  defines   that  the  predicate  cannot  be
%   redefined inside a module.

%!  '$clausable'(+Spec) is det.
%
%   Specify that we can run  clause/2  on   a  predicate,  even if it is
%   static. ISO specifies that `public` also   plays  this role. in SWI,
%   `public` means that the predicate can be   called, even if we cannot
%   find a reference to it.

%!  '$hide'(+Spec) is det.
%
%   Specify that the predicate cannot be seen in the debugger.

dynamic(Spec)            :- '$set_pattr'(Spec, pred, dynamic(true)).
multifile(Spec)          :- '$set_pattr'(Spec, pred, multifile(true)).
module_transparent(Spec) :- '$set_pattr'(Spec, pred, transparent(true)).
discontiguous(Spec)      :- '$set_pattr'(Spec, pred, discontiguous(true)).
volatile(Spec)           :- '$set_pattr'(Spec, pred, volatile(true)).
thread_local(Spec)       :- '$set_pattr'(Spec, pred, thread_local(true)).
noprofile(Spec)          :- '$set_pattr'(Spec, pred, noprofile(true)).
public(Spec)             :- '$set_pattr'(Spec, pred, public(true)).
non_terminal(Spec)       :- '$set_pattr'(Spec, pred, non_terminal(true)).
det(Spec)                :- '$set_pattr'(Spec, pred, det(true)).
'$iso'(Spec)             :- '$set_pattr'(Spec, pred, iso(true)).
'$clausable'(Spec)       :- '$set_pattr'(Spec, pred, clausable(true)).
'$hide'(Spec)            :- '$set_pattr'(Spec, pred, trace(false)).
'$notransact'(Spec)      :- '$set_pattr'(Spec, pred, transact(false)).

'$set_pattr'(M:Pred, How, Attr) :-
    '$set_pattr'(Pred, M, How, Attr).

%!  '$set_pattr'(+Spec, +Module, +From, +Attr)
%
%   Set predicate attributes. From is one of `pred` or `directive`.

'$set_pattr'(X, _, _, _) :-
    var(X),
    '$uninstantiation_error'(X).
'$set_pattr'(as(Spec,Options), M, How, Attr0) :-
    !,
    '$attr_options'(Options, Attr0, Attr),
    '$set_pattr'(Spec, M, How, Attr).
'$set_pattr'([], _, _, _) :- !.
'$set_pattr'([H|T], M, How, Attr) :-           % ISO
    !,
    '$set_pattr'(H, M, How, Attr),
    '$set_pattr'(T, M, How, Attr).
'$set_pattr'((A,B), M, How, Attr) :-           % ISO and traditional
    !,
    '$set_pattr'(A, M, How, Attr),
    '$set_pattr'(B, M, How, Attr).
'$set_pattr'(M:T, _, How, Attr) :-
    !,
    '$set_pattr'(T, M, How, Attr).
'$set_pattr'(PI, M, _, []) :-
    !,
    '$pi_head'(M:PI, Pred),
    '$set_table_wrappers'(Pred).
'$set_pattr'(A, M, How, [O|OT]) :-
    !,
    '$set_pattr'(A, M, How, O),
    '$set_pattr'(A, M, How, OT).
'$set_pattr'(A, M, pred, Attr) :-
    !,
    Attr =.. [Name,Val],
    '$set_pi_attr'(M:A, Name, Val).
'$set_pattr'(A, M, directive, Attr) :-
    !,
    Attr =.. [Name,Val],
    catch('$set_pi_attr'(M:A, Name, Val),
	  error(E, _),
	  print_message(error, error(E, context((Name)/1,_)))).

'$set_pi_attr'(PI, Name, Val) :-
    '$pi_head'(PI, Head),
    '$set_predicate_attribute'(Head, Name, Val).

'$attr_options'(Var, _, _) :-
    var(Var),
    !,
    '$uninstantiation_error'(Var).
'$attr_options'((A,B), Attr0, Attr) :-
    !,
    '$attr_options'(A, Attr0, Attr1),
    '$attr_options'(B, Attr1, Attr).
'$attr_options'(Opt, Attr0, Attrs) :-
    '$must_be'(ground, Opt),
    (   '$attr_option'(Opt, AttrX)
    ->  (   is_list(Attr0)
	->  '$join_attrs'(AttrX, Attr0, Attrs)
	;   '$join_attrs'(AttrX, [Attr0], Attrs)
	)
    ;   '$domain_error'(predicate_option, Opt)
    ).

'$join_attrs'([], Attrs, Attrs) :-
    !.
'$join_attrs'([H|T], Attrs0, Attrs) :-
    !,
    '$join_attrs'(H, Attrs0, Attrs1),
    '$join_attrs'(T, Attrs1, Attrs).
'$join_attrs'(Attr, Attrs, Attrs) :-
    memberchk(Attr, Attrs),
    !.
'$join_attrs'(Attr, Attrs, Attrs) :-
    Attr =.. [Name,Value],
    Gen =.. [Name,Existing],
    memberchk(Gen, Attrs),
    !,
    throw(error(conflict_error(Name, Value, Existing), _)).
'$join_attrs'(Attr, Attrs0, Attrs) :-
    '$append'(Attrs0, [Attr], Attrs).

'$attr_option'(incremental, [incremental(true),opaque(false)]).
'$attr_option'(monotonic, monotonic(true)).
'$attr_option'(lazy, lazy(true)).
'$attr_option'(opaque, [incremental(false),opaque(true)]).
'$attr_option'(abstract(Level0), abstract(Level)) :-
    '$table_option'(Level0, Level).
'$attr_option'(subgoal_abstract(Level0), subgoal_abstract(Level)) :-
    '$table_option'(Level0, Level).
'$attr_option'(answer_abstract(Level0), answer_abstract(Level)) :-
    '$table_option'(Level0, Level).
'$attr_option'(max_answers(Level0), max_answers(Level)) :-
    '$table_option'(Level0, Level).
'$attr_option'(volatile, volatile(true)).
'$attr_option'(multifile, multifile(true)).
'$attr_option'(discontiguous, discontiguous(true)).
'$attr_option'(shared, thread_local(false)).
'$attr_option'(local, thread_local(true)).
'$attr_option'(private, thread_local(true)).

'$table_option'(Value0, _Value) :-
    var(Value0),
    !,
    '$instantiation_error'(Value0).
'$table_option'(Value0, Value) :-
    integer(Value0),
    Value0 >= 0,
    !,
    Value = Value0.
'$table_option'(off, -1) :-
    !.
'$table_option'(false, -1) :-
    !.
'$table_option'(infinite, -1) :-
    !.
'$table_option'(Value, _) :-
    '$domain_error'(nonneg_or_false, Value).


%!  '$pattr_directive'(+Spec, +Module) is det.
%
%   This implements the directive version of dynamic/1, multifile/1,
%   etc. This version catches and prints   errors.  If the directive
%   specifies  multiple  predicates,  processing    after  an  error
%   continues with the remaining predicates.

'$pattr_directive'(dynamic(Spec), M) :-
    '$set_pattr'(Spec, M, directive, dynamic(true)).
'$pattr_directive'(multifile(Spec), M) :-
    '$set_pattr'(Spec, M, directive, multifile(true)).
'$pattr_directive'(module_transparent(Spec), M) :-
    '$set_pattr'(Spec, M, directive, transparent(true)).
'$pattr_directive'(discontiguous(Spec), M) :-
    '$set_pattr'(Spec, M, directive, discontiguous(true)).
'$pattr_directive'(volatile(Spec), M) :-
    '$set_pattr'(Spec, M, directive, volatile(true)).
'$pattr_directive'(thread_local(Spec), M) :-
    '$set_pattr'(Spec, M, directive, thread_local(true)).
'$pattr_directive'(noprofile(Spec), M) :-
    '$set_pattr'(Spec, M, directive, noprofile(true)).
'$pattr_directive'(public(Spec), M) :-
    '$set_pattr'(Spec, M, directive, public(true)).
'$pattr_directive'(det(Spec), M) :-
    '$set_pattr'(Spec, M, directive, det(true)).

%!  '$pi_head'(?PI, ?Head)

'$pi_head'(PI, Head) :-
    var(PI),
    var(Head),
    '$instantiation_error'([PI,Head]).
'$pi_head'(M:PI, M:Head) :-
    !,
    '$pi_head'(PI, Head).
'$pi_head'(Name/Arity, Head) :-
    !,
    '$head_name_arity'(Head, Name, Arity).
'$pi_head'(Name//DCGArity, Head) :-
    !,
    (   nonvar(DCGArity)
    ->  Arity is DCGArity+2,
	'$head_name_arity'(Head, Name, Arity)
    ;   '$head_name_arity'(Head, Name, Arity),
	DCGArity is Arity - 2
    ).
'$pi_head'(PI, _) :-
    '$type_error'(predicate_indicator, PI).

%!  '$head_name_arity'(+Goal, -Name, -Arity).
%!  '$head_name_arity'(-Goal, +Name, +Arity).

'$head_name_arity'(Goal, Name, Arity) :-
    (   atom(Goal)
    ->  Name = Goal, Arity = 0
    ;   compound(Goal)
    ->  compound_name_arity(Goal, Name, Arity)
    ;   var(Goal)
    ->  (   Arity == 0
	->  (   atom(Name)
	    ->  Goal = Name
	    ;   Name == []
	    ->  Goal = Name
	    ;   blob(Name, closure)
	    ->  Goal = Name
	    ;   '$type_error'(atom, Name)
	    )
	;   compound_name_arity(Goal, Name, Arity)
	)
    ;   '$type_error'(callable, Goal)
    ).

:- '$iso'(((dynamic)/1, (multifile)/1, (discontiguous)/1)).


		/********************************
		*       CALLING, CONTROL        *
		*********************************/

:- noprofile((call/1,
	      catch/3,
	      once/1,
	      ignore/1,
	      call_cleanup/2,
	      setup_call_cleanup/3,
	      setup_call_catcher_cleanup/4,
	      notrace/1)).

:- meta_predicate
    ';'(0,0),
    ','(0,0),
    @(0,+),
    call(0),
    call(1,?),
    call(2,?,?),
    call(3,?,?,?),
    call(4,?,?,?,?),
    call(5,?,?,?,?,?),
    call(6,?,?,?,?,?,?),
    call(7,?,?,?,?,?,?,?),
    not(0),
    \+(0),
    $(0),
    '->'(0,0),
    '*->'(0,0),
    once(0),
    ignore(0),
    catch(0,?,0),
    reset(0,?,-),
    setup_call_cleanup(0,0,0),
    setup_call_catcher_cleanup(0,0,?,0),
    call_cleanup(0,0),
    catch_with_backtrace(0,?,0),
    notrace(0),
    '$meta_call'(0).

:- '$iso'((call/1, (\+)/1, once/1, (;)/2, (',')/2, (->)/2, catch/3)).

% The control structures are always compiled, both   if they appear in a
% clause body and if they are handed  to   call/1.  The only way to call
% these predicates is by means of  call/2..   In  that case, we call the
% hole control structure again to get it compiled by call/1 and properly
% deal  with  !,  etc.  Another  reason  for  having  these  things   as
% predicates is to be able to define   properties for them, helping code
% analyzers.

(M0:If ; M0:Then) :- !, call(M0:(If ; Then)).
(M1:If ; M2:Then) :-    call(M1:(If ; M2:Then)).
(G1   , G2)       :-    call((G1   , G2)).
(If  -> Then)     :-    call((If  -> Then)).
(If *-> Then)     :-    call((If *-> Then)).
@(Goal,Module)    :-    @(Goal,Module).

%!  '$meta_call'(:Goal)
%
%   Interpreted  meta-call  implementation.  By    default,   call/1
%   compiles its argument into  a   temporary  clause. This realises
%   better  performance  if  the  (complex)  goal   does  a  lot  of
%   backtracking  because  this   interpreted    version   needs  to
%   re-interpret the remainder of the goal after backtracking.
%
%   This implementation is used by  reset/3 because the continuation
%   cannot be captured if it contains   a  such a compiled temporary
%   clause.

'$meta_call'(M:G) :-
    prolog_current_choice(Ch),
    '$meta_call'(G, M, Ch).

'$meta_call'(Var, _, _) :-
    var(Var),
    !,
    '$instantiation_error'(Var).
'$meta_call'((A,B), M, Ch) :-
    !,
    '$meta_call'(A, M, Ch),
    '$meta_call'(B, M, Ch).
'$meta_call'((I->T;E), M, Ch) :-
    !,
    (   prolog_current_choice(Ch2),
	'$meta_call'(I, M, Ch2)
    ->  '$meta_call'(T, M, Ch)
    ;   '$meta_call'(E, M, Ch)
    ).
'$meta_call'((I*->T;E), M, Ch) :-
    !,
    (   prolog_current_choice(Ch2),
	'$meta_call'(I, M, Ch2)
    *-> '$meta_call'(T, M, Ch)
    ;   '$meta_call'(E, M, Ch)
    ).
'$meta_call'((I->T), M, Ch) :-
    !,
    (   prolog_current_choice(Ch2),
	'$meta_call'(I, M, Ch2)
    ->  '$meta_call'(T, M, Ch)
    ).
'$meta_call'((I*->T), M, Ch) :-
    !,
    prolog_current_choice(Ch2),
    '$meta_call'(I, M, Ch2),
    '$meta_call'(T, M, Ch).
'$meta_call'((A;B), M, Ch) :-
    !,
    (   '$meta_call'(A, M, Ch)
    ;   '$meta_call'(B, M, Ch)
    ).
'$meta_call'(\+(G), M, _) :-
    !,
    prolog_current_choice(Ch),
    \+ '$meta_call'(G, M, Ch).
'$meta_call'($(G), M, _) :-
    !,
    prolog_current_choice(Ch),
    $('$meta_call'(G, M, Ch)).
'$meta_call'(call(G), M, _) :-
    !,
    prolog_current_choice(Ch),
    '$meta_call'(G, M, Ch).
'$meta_call'(M:G, _, Ch) :-
    !,
    '$meta_call'(G, M, Ch).
'$meta_call'(!, _, Ch) :-
    prolog_cut_to(Ch).
'$meta_call'(G, M, _Ch) :-
    call(M:G).

%!  call(:Closure, ?A).
%!  call(:Closure, ?A1, ?A2).
%!  call(:Closure, ?A1, ?A2, ?A3).
%!  call(:Closure, ?A1, ?A2, ?A3, ?A4).
%!  call(:Closure, ?A1, ?A2, ?A3, ?A4, ?A5).
%!  call(:Closure, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6).
%!  call(:Closure, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6, ?A7).
%
%   Arity 2..8 is demanded by the   ISO standard. Higher arities are
%   supported, but handled by the compiler.   This  implies they are
%   not backed up by predicates and   analyzers  thus cannot ask for
%   their  properties.  Analyzers  should    hard-code  handling  of
%   call/2..

:- '$iso'((call/2,
	   call/3,
	   call/4,
	   call/5,
	   call/6,
	   call/7,
	   call/8)).

call(Goal) :-                           % make these available as predicates
    Goal.
call(Goal, A) :-
    call(Goal, A).
call(Goal, A, B) :-
    call(Goal, A, B).
call(Goal, A, B, C) :-
    call(Goal, A, B, C).
call(Goal, A, B, C, D) :-
    call(Goal, A, B, C, D).
call(Goal, A, B, C, D, E) :-
    call(Goal, A, B, C, D, E).
call(Goal, A, B, C, D, E, F) :-
    call(Goal, A, B, C, D, E, F).
call(Goal, A, B, C, D, E, F, G) :-
    call(Goal, A, B, C, D, E, F, G).

%!  not(:Goal) is semidet.
%
%   Pre-ISO version of \+/1. Note that  some systems define not/1 as
%   a logically more sound version of \+/1.

not(Goal) :-
    \+ Goal.

%!  \+(:Goal) is semidet.
%
%   Predicate version that allows for meta-calling.

\+ Goal :-
    \+ Goal.

%!  once(:Goal) is semidet.
%
%   ISO predicate, acting as call((Goal, !)).

once(Goal) :-
    Goal,
    !.

%!  ignore(:Goal) is det.
%
%   Call Goal, cut choice-points on success  and succeed on failure.
%   intended for calling side-effects and proceed on failure.

ignore(Goal) :-
    Goal,
    !.
ignore(_Goal).

:- '$iso'((false/0)).

%!  false.
%
%   Synonym for fail/0, providing a declarative reading.

false :-
    fail.

%!  catch(:Goal, +Catcher, :Recover)
%
%   ISO compliant exception handling.

catch(_Goal, _Catcher, _Recover) :-
    '$catch'.                       % Maps to I_CATCH, I_EXITCATCH

%!  prolog_cut_to(+Choice)
%
%   Cut all choice points after Choice

prolog_cut_to(_Choice) :-
    '$cut'.                         % Maps to I_CUTCHP

%!  $ is det.
%
%   Declare that from now on this predicate succeeds deterministically.

'$' :- '$'.

%!  $(:Goal) is det.
%
%   Declare that Goal must succeed deterministically.

$(Goal) :- $(Goal).

%!  notrace(:Goal) is semidet.
%
%   Suspend the tracer while running Goal.

:- '$hide'(notrace/1).

notrace(Goal) :-
    setup_call_cleanup(
	'$notrace'(Flags, SkipLevel),
	once(Goal),
	'$restore_trace'(Flags, SkipLevel)).


%!  reset(:Goal, ?Ball, -Continue)
%
%   Delimited continuation support.

reset(_Goal, _Ball, _Cont) :-
    '$reset'.

%!  shift(+Ball).
%!  shift_for_copy(+Ball).
%
%   Shift control back to the  enclosing   reset/3.  The  second version
%   assumes the continuation will be saved to   be reused in a different
%   context.

shift(Ball) :-
    '$shift'(Ball).

shift_for_copy(Ball) :-
    '$shift_for_copy'(Ball).

%!  call_continuation(+Continuation:list)
%
%   Call a continuation as created  by   shift/1.  The continuation is a
%   list of '$cont$'(Clause, PC, EnvironmentArg,   ...)  structures. The
%   predicate  '$call_one_tail_body'/1  creates   a    frame   from  the
%   continuation and calls this.
%
%   Note that we can technically also  push the entire continuation onto
%   the environment and  call  it.  Doing   it  incrementally  as  below
%   exploits last-call optimization  and   therefore  possible quadratic
%   expansion of the continuation.

call_continuation([]).
call_continuation([TB|Rest]) :-
    (   Rest == []
    ->  '$call_continuation'(TB)
    ;   '$call_continuation'(TB),
	call_continuation(Rest)
    ).

%!  catch_with_backtrace(:Goal, ?Ball, :Recover)
%
%   As catch/3, but tell library(prolog_stack) to  record a backtrace in
%   case of an exception.

catch_with_backtrace(Goal, Ball, Recover) :-
    catch(Goal, Ball, Recover),
    '$no_lco'.

'$no_lco'.

%!  '$recover_and_rethrow'(:Goal, +Term)
%
%   This goal is used  to  wrap  the   catch/3  recover  handler  if the
%   exception is not  supposed  to  be   `catchable'.  This  applies  to
%   exceptions of the shape unwind(Term).  Note   that  we cut to ensure
%   that the exception is  not  delayed   forever  because  the  recover
%   handler leaves a choicepoint.

:- public '$recover_and_rethrow'/2.

'$recover_and_rethrow'(Goal, Exception) :-
    call_cleanup(Goal, throw(Exception)),
    !.


%!  call_cleanup(:Goal, :Cleanup).
%!  setup_call_cleanup(:Setup, :Goal, :Cleanup).
%!  setup_call_catcher_cleanup(:Setup, :Goal, +Catcher, :Cleanup).
%
%   Call Cleanup once after  Goal   is  finished (deterministic success,
%   failure,  exception  or  cut).  The    call  to  '$call_cleanup'  is
%   translated   to   ``I_CALLCLEANUP``,     ``I_EXITCLEANUP``.    These
%   instructions  rely  on  the  exact  stack    layout  left  by  these
%   predicates, where the variant is determined   by the arity. See also
%   callCleanupHandler() in `pl-wam.c`.

setup_call_catcher_cleanup(Setup, _Goal, _Catcher, _Cleanup) :-
    sig_atomic(Setup),
    '$call_cleanup'.

setup_call_cleanup(Setup, _Goal, _Cleanup) :-
    sig_atomic(Setup),
    '$call_cleanup'.

call_cleanup(_Goal, _Cleanup) :-
    '$call_cleanup'.


		 /*******************************
		 *       INITIALIZATION         *
		 *******************************/

:- meta_predicate
    initialization(0, +).

:- multifile '$init_goal'/3.
:- dynamic   '$init_goal'/3.
:- '$notransact'('$init_goal'/3).

%!  initialization(:Goal, +When)
%
%   Register Goal to be executed if a saved state is restored. In
%   addition, the goal is executed depending on When:
%
%       * now
%       Execute immediately
%       * after_load
%       Execute after loading the file in which it appears.  This
%       is initialization/1.
%       * restore_state
%       Do not execute immediately, but only when restoring the
%       state.  Not allowed in a sandboxed environment.
%       * prepare_state
%       Called before saving a state.  Can be used to clean the
%       environment (see also volatile/1) or eagerly execute
%       goals that are normally executed lazily.
%       * program
%       Works as =|-g goal|= goals.
%       * main
%       Starts the application.  Only last declaration is used.
%
%   Note that all goals are executed when a program is restored.

initialization(Goal, When) :-
    '$must_be'(oneof(atom, initialization_type,
		     [ now,
		       after_load,
		       restore,
		       restore_state,
		       prepare_state,
		       program,
		       main
		     ]), When),
    '$initialization_context'(Source, Ctx),
    '$initialization'(When, Goal, Source, Ctx).

'$initialization'(now, Goal, _Source, Ctx) :-
    '$run_init_goal'(Goal, Ctx),
    '$compile_init_goal'(-, Goal, Ctx).
'$initialization'(after_load, Goal, Source, Ctx) :-
    (   Source \== (-)
    ->  '$compile_init_goal'(Source, Goal, Ctx)
    ;   throw(error(context_error(nodirective,
				  initialization(Goal, after_load)),
		    _))
    ).
'$initialization'(restore, Goal, Source, Ctx) :- % deprecated
    '$initialization'(restore_state, Goal, Source, Ctx).
'$initialization'(restore_state, Goal, _Source, Ctx) :-
    (   \+ current_prolog_flag(sandboxed_load, true)
    ->  '$compile_init_goal'(-, Goal, Ctx)
    ;   '$permission_error'(register, initialization(restore), Goal)
    ).
'$initialization'(prepare_state, Goal, _Source, Ctx) :-
    (   \+ current_prolog_flag(sandboxed_load, true)
    ->  '$compile_init_goal'(when(prepare_state), Goal, Ctx)
    ;   '$permission_error'(register, initialization(restore), Goal)
    ).
'$initialization'(program, Goal, _Source, Ctx) :-
    (   \+ current_prolog_flag(sandboxed_load, true)
    ->  '$compile_init_goal'(when(program), Goal, Ctx)
    ;   '$permission_error'(register, initialization(restore), Goal)
    ).
'$initialization'(main, Goal, _Source, Ctx) :-
    (   \+ current_prolog_flag(sandboxed_load, true)
    ->  '$compile_init_goal'(when(main), Goal, Ctx)
    ;   '$permission_error'(register, initialization(restore), Goal)
    ).


'$compile_init_goal'(Source, Goal, Ctx) :-
    atom(Source),
    Source \== (-),
    !,
    '$store_admin_clause'(system:'$init_goal'(Source, Goal, Ctx),
			  _Layout, Source, Ctx).
'$compile_init_goal'(Source, Goal, Ctx) :-
    assertz('$init_goal'(Source, Goal, Ctx)).


%!  '$run_initialization'(?File, +Options) is det.
%!  '$run_initialization'(?File, +Action, +Options) is det.
%
%   Run initialization directives for all files  if File is unbound,
%   or for a specified file.   Note  that '$run_initialization'/2 is
%   called from runInitialization() in pl-wic.c  for .qlf files. The
%   '$run_initialization'/3 is called with Action   set  to `loaded`
%   when called for a QLF file.

'$run_initialization'(_, loaded, _) :- !.
'$run_initialization'(File, _Action, Options) :-
    '$run_initialization'(File, Options).

'$run_initialization'(File, Options) :-
    setup_call_cleanup(
	'$start_run_initialization'(Options, Restore),
	'$run_initialization_2'(File),
	'$end_run_initialization'(Restore)).

'$start_run_initialization'(Options, OldSandBoxed) :-
    '$push_input_context'(initialization),
    '$set_sandboxed_load'(Options, OldSandBoxed).
'$end_run_initialization'(OldSandBoxed) :-
    set_prolog_flag(sandboxed_load, OldSandBoxed),
    '$pop_input_context'.

'$run_initialization_2'(File) :-
    (   '$init_goal'(File, Goal, Ctx),
	File \= when(_),
	'$run_init_goal'(Goal, Ctx),
	fail
    ;   true
    ).

'$run_init_goal'(Goal, Ctx) :-
    (   catch_with_backtrace('$run_init_goal'(Goal), E,
			     '$initialization_error'(E, Goal, Ctx))
    ->  true
    ;   '$initialization_failure'(Goal, Ctx)
    ).

:- multifile prolog:sandbox_allowed_goal/1.

'$run_init_goal'(Goal) :-
    current_prolog_flag(sandboxed_load, false),
    !,
    call(Goal).
'$run_init_goal'(Goal) :-
    prolog:sandbox_allowed_goal(Goal),
    call(Goal).

'$initialization_context'(Source, Ctx) :-
    (   source_location(File, Line)
    ->  Ctx = File:Line,
	'$input_context'(Context),
	'$top_file'(Context, File, Source)
    ;   Ctx = (-),
	File = (-)
    ).

'$top_file'([input(include, F1, _, _)|T], _, F) :-
    !,
    '$top_file'(T, F1, F).
'$top_file'(_, F, F).


'$initialization_error'(E, Goal, Ctx) :-
    print_message(error, initialization_error(Goal, E, Ctx)).

'$initialization_failure'(Goal, Ctx) :-
    print_message(warning, initialization_failure(Goal, Ctx)).

%!  '$clear_source_admin'(+File) is det.
%
%   Removes source adminstration related to File
%
%   @see Called from destroySourceFile() in pl-proc.c

:- public '$clear_source_admin'/1.

'$clear_source_admin'(File) :-
    retractall('$init_goal'(_, _, File:_)),
    retractall('$load_context_module'(File, _, _)),
    retractall('$resolved_source_path_db'(_, _, File)).


		 /*******************************
		 *            STREAM            *
		 *******************************/

:- '$iso'(stream_property/2).
stream_property(Stream, Property) :-
    nonvar(Stream),
    nonvar(Property),
    !,
    '$stream_property'(Stream, Property).
stream_property(Stream, Property) :-
    nonvar(Stream),
    !,
    '$stream_properties'(Stream, Properties),
    '$member'(Property, Properties).
stream_property(Stream, Property) :-
    nonvar(Property),
    !,
    (   Property = alias(Alias),
	atom(Alias)
    ->  '$alias_stream'(Alias, Stream)
    ;   '$streams_properties'(Property, Pairs),
	'$member'(Stream-Property, Pairs)
    ).
stream_property(Stream, Property) :-
    '$streams_properties'(Property, Pairs),
    '$member'(Stream-Properties, Pairs),
    '$member'(Property, Properties).


		/********************************
		*            MODULES            *
		*********************************/

%       '$prefix_module'(+Module, +Context, +Term, -Prefixed)
%       Tags `Term' with `Module:' if `Module' is not the context module.

'$prefix_module'(Module, Module, Head, Head) :- !.
'$prefix_module'(Module, _, Head, Module:Head).

%!  default_module(+Me, -Super) is multi.
%
%   Is true if `Super' is `Me' or a super (auto import) module of `Me'.

default_module(Me, Super) :-
    (   atom(Me)
    ->  (   var(Super)
	->  '$default_module'(Me, Super)
	;   '$default_module'(Me, Super), !
	)
    ;   '$type_error'(module, Me)
    ).

'$default_module'(Me, Me).
'$default_module'(Me, Super) :-
    import_module(Me, S),
    '$default_module'(S, Super).


		/********************************
		*      TRACE AND EXCEPTIONS     *
		*********************************/

:- dynamic   user:exception/3.
:- multifile user:exception/3.
:- '$hide'(user:exception/3).

%!  '$undefined_procedure'(+Module, +Name, +Arity, -Action) is det.
%
%   This predicate is called from C   on undefined predicates. First
%   allows the user to take care of   it using exception/3. Else try
%   to give a DWIM warning. Otherwise fail.   C  will print an error
%   message.

:- public
    '$undefined_procedure'/4.

'$undefined_procedure'(Module, Name, Arity, Action) :-
    '$prefix_module'(Module, user, Name/Arity, Pred),
    user:exception(undefined_predicate, Pred, Action0),
    !,
    Action = Action0.
'$undefined_procedure'(Module, Name, Arity, Action) :-
    \+ current_prolog_flag(autoload, false),
    '$autoload'(Module:Name/Arity),
    !,
    Action = retry.
'$undefined_procedure'(_, _, _, error).


%!  '$loading'(+Library)
%
%   True if the library  is  being   loaded.  Just  testing that the
%   predicate is defined is not  good  enough   as  the  file may be
%   partly  loaded.  Calling  use_module/2  at   any  time  has  two
%   drawbacks: it queries the filesystem,   causing  slowdown and it
%   stops libraries being autoloaded from a   saved  state where the
%   library is already loaded, but the source may not be accessible.

'$loading'(Library) :-
    current_prolog_flag(threads, true),
    (   '$loading_file'(Library, _Queue, _LoadThread)
    ->  true
    ;   '$loading_file'(FullFile, _Queue, _LoadThread),
	file_name_extension(Library, _, FullFile)
    ->  true
    ).

%        handle debugger 'w', 'p' and <N> depth options.

'$set_debugger_write_options'(write) :-
    !,
    create_prolog_flag(debugger_write_options,
		       [ quoted(true),
			 attributes(dots),
			 spacing(next_argument)
		       ], []).
'$set_debugger_write_options'(print) :-
    !,
    create_prolog_flag(debugger_write_options,
		       [ quoted(true),
			 portray(true),
			 max_depth(10),
			 attributes(portray),
			 spacing(next_argument)
		       ], []).
'$set_debugger_write_options'(Depth) :-
    current_prolog_flag(debugger_write_options, Options0),
    (   '$select'(max_depth(_), Options0, Options)
    ->  true
    ;   Options = Options0
    ),
    create_prolog_flag(debugger_write_options,
		       [max_depth(Depth)|Options], []).


		/********************************
		*        SYSTEM MESSAGES        *
		*********************************/

%!  '$confirm'(Spec) is semidet.
%
%   Ask the user  to confirm a question.   Spec is a term  as used for
%   print_message/2.   It is  printed the  the `query`  channel.  This
%   predicate may be hooked  using prolog:confirm/2, which must return
%   a boolean.

:- multifile
    prolog:confirm/2.

'$confirm'(Spec) :-
    prolog:confirm(Spec, Result),
    !,
    Result == true.
'$confirm'(Spec) :-
    print_message(query, Spec),
    between(0, 5, _),
	get_single_char(Answer),
	(   '$in_reply'(Answer, 'yYjJ \n')
	->  !,
	    print_message(query, if_tty([yes-[]]))
	;   '$in_reply'(Answer, 'nN')
	->  !,
	    print_message(query, if_tty([no-[]])),
	    fail
	;   print_message(help, query(confirm)),
	    fail
	).

'$in_reply'(Code, Atom) :-
    char_code(Char, Code),
    sub_atom(Atom, _, _, _, Char),
    !.

:- dynamic
    user:portray/1.
:- multifile
    user:portray/1.
:- '$notransact'(user:portray/1).


		 /*******************************
		 *       FILE_SEARCH_PATH       *
		 *******************************/

:- dynamic
    user:file_search_path/2,
    user:library_directory/1.
:- multifile
    user:file_search_path/2,
    user:library_directory/1.
:- '$notransact'((user:file_search_path/2,
                  user:library_directory/1)).

user:(file_search_path(library, Dir) :-
	library_directory(Dir)).
user:file_search_path(swi, Home) :-
    current_prolog_flag(home, Home).
user:file_search_path(swi, Home) :-
    current_prolog_flag(shared_home, Home).
user:file_search_path(library, app_config(lib)).
user:file_search_path(library, swi(library)).
user:file_search_path(library, swi(library/clp)).
user:file_search_path(library, Dir) :-
    '$ext_library_directory'(Dir).
user:file_search_path(path, Dir) :-
    getenv('PATH', Path),
    current_prolog_flag(path_sep, Sep),
    atomic_list_concat(Dirs, Sep, Path),
    '$member'(Dir, Dirs).
user:file_search_path(user_app_data, Dir) :-
    '$xdg_prolog_directory'(data, Dir).
user:file_search_path(common_app_data, Dir) :-
    '$xdg_prolog_directory'(common_data, Dir).
user:file_search_path(user_app_config, Dir) :-
    '$xdg_prolog_directory'(config, Dir).
user:file_search_path(common_app_config, Dir) :-
    '$xdg_prolog_directory'(common_config, Dir).
user:file_search_path(app_data, user_app_data('.')).
user:file_search_path(app_data, common_app_data('.')).
user:file_search_path(app_config, user_app_config('.')).
user:file_search_path(app_config, common_app_config('.')).
% backward compatibility
user:file_search_path(app_preferences, user_app_config('.')).
user:file_search_path(user_profile, app_preferences('.')).
user:file_search_path(app, swi(app)).
user:file_search_path(app, app_data(app)).
user:file_search_path(working_directory, CWD) :-
    working_directory(CWD, CWD).

'$xdg_prolog_directory'(Which, Dir) :-
    '$xdg_directory'(Which, XDGDir),
    '$make_config_dir'(XDGDir),
    '$ensure_slash'(XDGDir, XDGDirS),
    atom_concat(XDGDirS, 'swi-prolog', Dir),
    '$make_config_dir'(Dir).

'$xdg_directory'(Which, Dir) :-
    '$xdg_directory_search'(Where),
    '$xdg_directory'(Which, Where, Dir).

'$xdg_directory_search'(xdg) :-
    current_prolog_flag(xdg, true),
    !.
'$xdg_directory_search'(Where) :-
    current_prolog_flag(windows, true),
    (   current_prolog_flag(xdg, false)
    ->  Where = windows
    ;   '$member'(Where, [windows, xdg])
    ).

% config
'$xdg_directory'(config, windows, Home) :-
    catch(win_folder(appdata, Home), _, fail).
'$xdg_directory'(config, xdg, Home) :-
    getenv('XDG_CONFIG_HOME', Home).
'$xdg_directory'(config, xdg, Home) :-
    expand_file_name('~/.config', [Home]).
% data
'$xdg_directory'(data, windows, Home) :-
    catch(win_folder(local_appdata, Home), _, fail).
'$xdg_directory'(data, xdg, Home) :-
    getenv('XDG_DATA_HOME', Home).
'$xdg_directory'(data, xdg, Home) :-
    expand_file_name('~/.local', [Local]),
    '$make_config_dir'(Local),
    atom_concat(Local, '/share', Home),
    '$make_config_dir'(Home).
% common data
'$xdg_directory'(common_data, windows, Dir) :-
    catch(win_folder(common_appdata, Dir), _, fail).
'$xdg_directory'(common_data, xdg, Dir) :-
    '$existing_dir_from_env_path'('XDG_DATA_DIRS',
				  [ '/usr/local/share',
				    '/usr/share'
				  ],
				  Dir).
% common config
'$xdg_directory'(common_config, windows, Dir) :-
    catch(win_folder(common_appdata, Dir), _, fail).
'$xdg_directory'(common_config, xdg, Dir) :-
    '$existing_dir_from_env_path'('XDG_CONFIG_DIRS', ['/etc/xdg'], Dir).

'$existing_dir_from_env_path'(Env, Defaults, Dir) :-
    (   getenv(Env, Path)
    ->  current_prolog_flag(path_sep, Sep),
	atomic_list_concat(Dirs, Sep, Path)
    ;   Dirs = Defaults
    ),
    '$member'(Dir, Dirs),
    Dir \== '',
    exists_directory(Dir).

'$make_config_dir'(Dir) :-
    exists_directory(Dir),
    !.
'$make_config_dir'(Dir) :-
    nb_current('$create_search_directories', true),
    file_directory_name(Dir, Parent),
    '$my_file'(Parent),
    catch(make_directory(Dir), _, fail).

'$ensure_slash'(Dir, DirS) :-
    (   sub_atom(Dir, _, _, 0, /)
    ->  DirS = Dir
    ;   atom_concat(Dir, /, DirS)
    ).

:- dynamic '$ext_lib_dirs'/1.
:- volatile '$ext_lib_dirs'/1.

'$ext_library_directory'(Dir) :-
    '$ext_lib_dirs'(Dirs),
    !,
    '$member'(Dir, Dirs).
'$ext_library_directory'(Dir) :-
    current_prolog_flag(home, Home),
    atom_concat(Home, '/library/ext/*', Pattern),
    expand_file_name(Pattern, Dirs0),
    '$include'(exists_directory, Dirs0, Dirs),
    asserta('$ext_lib_dirs'(Dirs)),
    '$member'(Dir, Dirs).


%!  '$expand_file_search_path'(+Spec, -Expanded, +Cond) is nondet.

'$expand_file_search_path'(Spec, Expanded, Cond) :-
    '$option'(access(Access), Cond),
    memberchk(Access, [write,append]),
    !,
    setup_call_cleanup(
	nb_setval('$create_search_directories', true),
	expand_file_search_path(Spec, Expanded),
	nb_delete('$create_search_directories')).
'$expand_file_search_path'(Spec, Expanded, _Cond) :-
    expand_file_search_path(Spec, Expanded).

%!  expand_file_search_path(+Spec, -Expanded) is nondet.
%
%   Expand a search path.  The system uses depth-first search upto a
%   specified depth.  If this depth is exceeded an exception is raised.
%   TBD: bread-first search?

expand_file_search_path(Spec, Expanded) :-
    catch('$expand_file_search_path'(Spec, Expanded, 0, []),
	  loop(Used),
	  throw(error(loop_error(Spec), file_search(Used)))).

'$expand_file_search_path'(Spec, Expanded, N, Used) :-
    functor(Spec, Alias, 1),
    !,
    user:file_search_path(Alias, Exp0),
    NN is N + 1,
    (   NN > 16
    ->  throw(loop(Used))
    ;   true
    ),
    '$expand_file_search_path'(Exp0, Exp1, NN, [Alias=Exp0|Used]),
    arg(1, Spec, Segments),
    '$segments_to_atom'(Segments, File),
    '$make_path'(Exp1, File, Expanded).
'$expand_file_search_path'(Spec, Path, _, _) :-
    '$segments_to_atom'(Spec, Path).

'$make_path'(Dir, '.', Path) :-
    !,
    Path = Dir.
'$make_path'(Dir, File, Path) :-
    sub_atom(Dir, _, _, 0, /),
    !,
    atom_concat(Dir, File, Path).
'$make_path'(Dir, File, Path) :-
    atomic_list_concat([Dir, /, File], Path).


		/********************************
		*         FILE CHECKING         *
		*********************************/

%!  absolute_file_name(+Term, -AbsoluteFile, +Options) is nondet.
%
%   Translate path-specifier into a full   path-name. This predicate
%   originates from Quintus was introduced  in SWI-Prolog very early
%   and  has  re-appeared  in  SICStus  3.9.0,  where  they  changed
%   argument order and added some options.   We addopted the SICStus
%   argument order, but still accept the original argument order for
%   compatibility reasons.

absolute_file_name(Spec, Options, Path) :-
    '$is_options'(Options),
    \+ '$is_options'(Path),
    !,
    '$absolute_file_name'(Spec, Path, Options).
absolute_file_name(Spec, Path, Options) :-
    '$absolute_file_name'(Spec, Path, Options).

'$absolute_file_name'(Spec, Path, Options0) :-
    '$options_dict'(Options0, Options),
		    % get the valid extensions
    (   '$select_option'(extensions(Exts), Options, Options1)
    ->  '$must_be'(list, Exts)
    ;   '$option'(file_type(Type), Options)
    ->  '$must_be'(atom, Type),
	'$file_type_extensions'(Type, Exts),
	Options1 = Options
    ;   Options1 = Options,
	Exts = ['']
    ),
    '$canonicalise_extensions'(Exts, Extensions),
		    % unless specified otherwise, ask regular file
    (   (   nonvar(Type)
	;   '$option'(access(none), Options, none)
	)
    ->  Options2 = Options1
    ;   '$merge_options'(_{file_type:regular}, Options1, Options2)
    ),
		    % Det or nondet?
    (   '$select_option'(solutions(Sols), Options2, Options3)
    ->  '$must_be'(oneof(atom, solutions, [first,all]), Sols)
    ;   Sols = first,
	Options3 = Options2
    ),
		    % Errors or not?
    (   '$select_option'(file_errors(FileErrors), Options3, Options4)
    ->  '$must_be'(oneof(atom, file_errors, [error,fail]), FileErrors)
    ;   FileErrors = error,
	Options4 = Options3
    ),
		    % Expand shell patterns?
    (   atomic(Spec),
	'$select_option'(expand(Expand), Options4, Options5),
	'$must_be'(boolean, Expand)
    ->  expand_file_name(Spec, List),
	'$member'(Spec1, List)
    ;   Spec1 = Spec,
	Options5 = Options4
    ),
		    % Search for files
    (   Sols == first
    ->  (   '$chk_file'(Spec1, Extensions, Options5, true, Path)
	->  !       % also kill choice point of expand_file_name/2
	;   (   FileErrors == fail
	    ->  fail
	    ;   '$current_module'('$bags', _File),
		findall(P,
			'$chk_file'(Spec1, Extensions, [access(exist)],
				    false, P),
			Candidates),
		'$abs_file_error'(Spec, Candidates, Options5)
	    )
	)
    ;   '$chk_file'(Spec1, Extensions, Options5, false, Path)
    ).

'$abs_file_error'(Spec, Candidates, Conditions) :-
    '$member'(F, Candidates),
    '$member'(C, Conditions),
    '$file_condition'(C),
    '$file_error'(C, Spec, F, E, Comment),
    !,
    throw(error(E, context(_, Comment))).
'$abs_file_error'(Spec, _, _) :-
    '$existence_error'(source_sink, Spec).

'$file_error'(file_type(directory), Spec, File, Error, Comment) :-
    \+ exists_directory(File),
    !,
    Error = existence_error(directory, Spec),
    Comment = not_a_directory(File).
'$file_error'(file_type(_), Spec, File, Error, Comment) :-
    exists_directory(File),
    !,
    Error = existence_error(file, Spec),
    Comment = directory(File).
'$file_error'(access(OneOrList), Spec, File, Error, _) :-
    '$one_or_member'(Access, OneOrList),
    \+ access_file(File, Access),
    Error = permission_error(Access, source_sink, Spec).

'$one_or_member'(Elem, List) :-
    is_list(List),
    !,
    '$member'(Elem, List).
'$one_or_member'(Elem, Elem).

'$file_type_extensions'(Type, Exts) :-
    '$current_module'('$bags', _File),
    !,
    findall(Ext, user:prolog_file_type(Ext, Type), Exts0),
    (   Exts0 == [],
	\+ '$ft_no_ext'(Type)
    ->  '$domain_error'(file_type, Type)
    ;   true
    ),
    '$append'(Exts0, [''], Exts).
'$file_type_extensions'(prolog, [pl, '']). % findall is not yet defined ...

'$ft_no_ext'(txt).
'$ft_no_ext'(executable).
'$ft_no_ext'(directory).
'$ft_no_ext'(regular).

%!  user:prolog_file_type(?Extension, ?Type)
%
%   Define type of file based on the extension.  This is used by
%   absolute_file_name/3 and may be used to extend the list of
%   extensions used for some type.
%
%   Note that =qlf= must be last   when  searching for Prolog files.
%   Otherwise use_module/1 will consider  the   file  as  not-loaded
%   because the .qlf file is not  the   loaded  file.  Must be fixed
%   elsewhere.

:- multifile(user:prolog_file_type/2).
:- dynamic(user:prolog_file_type/2).

user:prolog_file_type(pl,       prolog).
user:prolog_file_type(prolog,   prolog).
user:prolog_file_type(qlf,      prolog).
user:prolog_file_type(pl,       source).
user:prolog_file_type(prolog,   source).
user:prolog_file_type(qlf,      qlf).
user:prolog_file_type(Ext,      executable) :-
    current_prolog_flag(shared_object_extension, Ext).
user:prolog_file_type(dylib,    executable) :-
    current_prolog_flag(apple,  true).

%!  '$chk_file'(+Spec, +Extensions, +Cond, +UseCache, -FullName)
%
%   File is a specification of a Prolog source file. Return the full
%   path of the file.

'$chk_file'(Spec, _Extensions, _Cond, _Cache, _FullName) :-
    \+ ground(Spec),
    !,
    '$instantiation_error'(Spec).
'$chk_file'(Spec, Extensions, Cond, Cache, FullName) :-
    compound(Spec),
    functor(Spec, _, 1),
    !,
    '$relative_to'(Cond, cwd, CWD),
    '$chk_alias_file'(Spec, Extensions, Cond, Cache, CWD, FullName).
'$chk_file'(Segments, Ext, Cond, Cache, FullName) :-    % allow a/b/...
    \+ atomic(Segments),
    !,
    '$segments_to_atom'(Segments, Atom),
    '$chk_file'(Atom, Ext, Cond, Cache, FullName).
'$chk_file'(File, Exts, Cond, _, FullName) :-           % Absolute files
    is_absolute_file_name(File),
    !,
    '$extend_file'(File, Exts, Extended),
    '$file_conditions'(Cond, Extended),
    '$absolute_file_name'(Extended, FullName).
'$chk_file'(File, Exts, Cond, _, FullName) :-           % Explicit relative_to
    '$option'(relative_to(_), Cond),
    !,
    '$relative_to'(Cond, none, Dir),
    '$chk_file_relative_to'(File, Exts, Cond, Dir, FullName).
'$chk_file'(File, Exts, Cond, _Cache, FullName) :-      % From source
    source_location(ContextFile, _Line),
    !,
    (   file_directory_name(ContextFile, Dir),
        '$chk_file_relative_to'(File, Exts, Cond, Dir, FullName)
    ->  true
    ;   current_prolog_flag(source_search_working_directory, true),
	'$extend_file'(File, Exts, Extended),
	'$file_conditions'(Cond, Extended),
	'$absolute_file_name'(Extended, FullName),
        '$print_message'(warning,
                         deprecated(source_search_working_directory(
                                        File, FullName)))
    ).
'$chk_file'(File, Exts, Cond, _Cache, FullName) :-      % Not loading source
    '$extend_file'(File, Exts, Extended),
    '$file_conditions'(Cond, Extended),
    '$absolute_file_name'(Extended, FullName).

'$chk_file_relative_to'(File, Exts, Cond, Dir, FullName) :-
    atomic_list_concat([Dir, /, File], AbsFile),
    '$extend_file'(AbsFile, Exts, Extended),
    '$file_conditions'(Cond, Extended),
    '$absolute_file_name'(Extended, FullName).


'$segments_to_atom'(Atom, Atom) :-
    atomic(Atom),
    !.
'$segments_to_atom'(Segments, Atom) :-
    '$segments_to_list'(Segments, List, []),
    !,
    atomic_list_concat(List, /, Atom).

'$segments_to_list'(A/B, H, T) :-
    '$segments_to_list'(A, H, T0),
    '$segments_to_list'(B, T0, T).
'$segments_to_list'(A, [A|T], T) :-
    atomic(A).


%!  '$relative_to'(+Condition, +Default, -Dir)
%
%   Determine the directory to work from.  This can be specified
%   explicitely using one or more relative_to(FileOrDir) options
%   or implicitely relative to the working directory or current
%   source-file.

'$relative_to'(Conditions, Default, Dir) :-
    (   '$option'(relative_to(FileOrDir), Conditions)
    *-> (   exists_directory(FileOrDir)
	->  Dir = FileOrDir
	;   atom_concat(Dir, /, FileOrDir)
	->  true
	;   file_directory_name(FileOrDir, Dir)
	)
    ;   Default == cwd
    ->  working_directory(Dir, Dir)
    ;   Default == source
    ->  source_location(ContextFile, _Line),
	file_directory_name(ContextFile, Dir)
    ).

%!  '$chk_alias_file'(+Spec, +Exts, +Cond, +Cache, +CWD,
%!                    -FullFile) is nondet.

:- dynamic
    '$search_path_file_cache'/3,    % SHA1, Time, Path
    '$search_path_gc_time'/1.       % Time
:- volatile
    '$search_path_file_cache'/3,
    '$search_path_gc_time'/1.
:- '$notransact'(('$search_path_file_cache'/3,
                  '$search_path_gc_time'/1)).

:- create_prolog_flag(file_search_cache_time, 10, []).

'$chk_alias_file'(Spec, Exts, Cond, true, CWD, FullFile) :-
    !,
    findall(Exp, '$expand_file_search_path'(Spec, Exp, Cond), Expansions),
    current_prolog_flag(emulated_dialect, Dialect),
    Cache = cache(Exts, Cond, CWD, Expansions, Dialect),
    variant_sha1(Spec+Cache, SHA1),
    get_time(Now),
    current_prolog_flag(file_search_cache_time, TimeOut),
    (   '$search_path_file_cache'(SHA1, CachedTime, FullFile),
	CachedTime > Now - TimeOut,
	'$file_conditions'(Cond, FullFile)
    ->  '$search_message'(file_search(cache(Spec, Cond), FullFile))
    ;   '$member'(Expanded, Expansions),
	'$extend_file'(Expanded, Exts, LibFile),
	(   '$file_conditions'(Cond, LibFile),
	    '$absolute_file_name'(LibFile, FullFile),
	    '$cache_file_found'(SHA1, Now, TimeOut, FullFile)
	->  '$search_message'(file_search(found(Spec, Cond), FullFile))
	;   '$search_message'(file_search(tried(Spec, Cond), LibFile)),
	    fail
	)
    ).
'$chk_alias_file'(Spec, Exts, Cond, false, _CWD, FullFile) :-
    '$expand_file_search_path'(Spec, Expanded, Cond),
    '$extend_file'(Expanded, Exts, LibFile),
    '$file_conditions'(Cond, LibFile),
    '$absolute_file_name'(LibFile, FullFile).

'$cache_file_found'(_, _, TimeOut, _) :-
    TimeOut =:= 0,
    !.
'$cache_file_found'(SHA1, Now, TimeOut, FullFile) :-
    '$search_path_file_cache'(SHA1, Saved, FullFile),
    !,
    (   Now - Saved < TimeOut/2
    ->  true
    ;   retractall('$search_path_file_cache'(SHA1, _, _)),
	asserta('$search_path_file_cache'(SHA1, Now, FullFile))
    ).
'$cache_file_found'(SHA1, Now, TimeOut, FullFile) :-
    'gc_file_search_cache'(TimeOut),
    asserta('$search_path_file_cache'(SHA1, Now, FullFile)).

'gc_file_search_cache'(TimeOut) :-
    get_time(Now),
    '$search_path_gc_time'(Last),
    Now-Last < TimeOut/2,
    !.
'gc_file_search_cache'(TimeOut) :-
    get_time(Now),
    retractall('$search_path_gc_time'(_)),
    assertz('$search_path_gc_time'(Now)),
    Before is Now - TimeOut,
    (   '$search_path_file_cache'(SHA1, Cached, FullFile),
	Cached < Before,
	retractall('$search_path_file_cache'(SHA1, Cached, FullFile)),
	fail
    ;   true
    ).


'$search_message'(Term) :-
    current_prolog_flag(verbose_file_search, true),
    !,
    print_message(informational, Term).
'$search_message'(_).


%!  '$file_conditions'(+Condition, +Path)
%
%   Verify Path satisfies Condition.

'$file_conditions'(List, File) :-
    is_list(List),
    !,
    \+ ( '$member'(C, List),
	 '$file_condition'(C),
	 \+ '$file_condition'(C, File)
       ).
'$file_conditions'(Map, File) :-
    \+ (  get_dict(Key, Map, Value),
	  C =.. [Key,Value],
	  '$file_condition'(C),
	 \+ '$file_condition'(C, File)
       ).

'$file_condition'(file_type(directory), File) :-
    !,
    exists_directory(File).
'$file_condition'(file_type(_), File) :-
    !,
    \+ exists_directory(File).
'$file_condition'(access(Accesses), File) :-
    !,
    \+ (  '$one_or_member'(Access, Accesses),
	  \+ access_file(File, Access)
       ).

'$file_condition'(exists).
'$file_condition'(file_type(_)).
'$file_condition'(access(_)).

'$extend_file'(File, Exts, FileEx) :-
    '$ensure_extensions'(Exts, File, Fs),
    '$list_to_set'(Fs, FsSet),
    '$member'(FileEx, FsSet).

'$ensure_extensions'([], _, []).
'$ensure_extensions'([E|E0], F, [FE|E1]) :-
    file_name_extension(F, E, FE),
    '$ensure_extensions'(E0, F, E1).

%!  '$list_to_set'(+List, -Set) is det.
%
%   Turn list into a set, keeping   the  left-most copy of duplicate
%   elements.  Copied from library(lists).

'$list_to_set'(List, Set) :-
    '$number_list'(List, 1, Numbered),
    sort(1, @=<, Numbered, ONum),
    '$remove_dup_keys'(ONum, NumSet),
    sort(2, @=<, NumSet, ONumSet),
    '$pairs_keys'(ONumSet, Set).

'$number_list'([], _, []).
'$number_list'([H|T0], N, [H-N|T]) :-
    N1 is N+1,
    '$number_list'(T0, N1, T).

'$remove_dup_keys'([], []).
'$remove_dup_keys'([H|T0], [H|T]) :-
    H = V-_,
    '$remove_same_key'(T0, V, T1),
    '$remove_dup_keys'(T1, T).

'$remove_same_key'([V1-_|T0], V, T) :-
    V1 == V,
    !,
    '$remove_same_key'(T0, V, T).
'$remove_same_key'(L, _, L).

'$pairs_keys'([], []).
'$pairs_keys'([K-_|T0], [K|T]) :-
    '$pairs_keys'(T0, T).

'$pairs_values'([], []).
'$pairs_values'([_-V|T0], [V|T]) :-
    '$pairs_values'(T0, T).

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Canonicalise the extension list. Old SWI-Prolog   require  `.pl', etc, which
the Quintus compatibility  requests  `pl'.   This  layer  canonicalises  all
extensions to .ext
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

'$canonicalise_extensions'([], []) :- !.
'$canonicalise_extensions'([H|T], [CH|CT]) :-
    !,
    '$must_be'(atom, H),
    '$canonicalise_extension'(H, CH),
    '$canonicalise_extensions'(T, CT).
'$canonicalise_extensions'(E, [CE]) :-
    '$canonicalise_extension'(E, CE).

'$canonicalise_extension'('', '') :- !.
'$canonicalise_extension'(DotAtom, DotAtom) :-
    sub_atom(DotAtom, 0, _, _, '.'),
    !.
'$canonicalise_extension'(Atom, DotAtom) :-
    atom_concat('.', Atom, DotAtom).


		/********************************
		*            CONSULT            *
		*********************************/

:- dynamic
    user:library_directory/1,
    user:prolog_load_file/2.
:- multifile
    user:library_directory/1,
    user:prolog_load_file/2.

:- prompt(_, '|: ').

:- thread_local
    '$compilation_mode_store'/1,    % database, wic, qlf
    '$directive_mode_store'/1.      % database, wic, qlf
:- volatile
    '$compilation_mode_store'/1,
    '$directive_mode_store'/1.
:- '$notransact'(('$compilation_mode_store'/1,
                  '$directive_mode_store'/1)).

'$compilation_mode'(Mode) :-
    (   '$compilation_mode_store'(Val)
    ->  Mode = Val
    ;   Mode = database
    ).

'$set_compilation_mode'(Mode) :-
    retractall('$compilation_mode_store'(_)),
    assertz('$compilation_mode_store'(Mode)).

'$compilation_mode'(Old, New) :-
    '$compilation_mode'(Old),
    (   New == Old
    ->  true
    ;   '$set_compilation_mode'(New)
    ).

'$directive_mode'(Mode) :-
    (   '$directive_mode_store'(Val)
    ->  Mode = Val
    ;   Mode = database
    ).

'$directive_mode'(Old, New) :-
    '$directive_mode'(Old),
    (   New == Old
    ->  true
    ;   '$set_directive_mode'(New)
    ).

'$set_directive_mode'(Mode) :-
    retractall('$directive_mode_store'(_)),
    assertz('$directive_mode_store'(Mode)).


%!  '$compilation_level'(-Level) is det.
%
%   True when Level reflects the nesting   in  files compiling other
%   files. 0 if no files are being loaded.

'$compilation_level'(Level) :-
    '$input_context'(Stack),
    '$compilation_level'(Stack, Level).

'$compilation_level'([], 0).
'$compilation_level'([Input|T], Level) :-
    (   arg(1, Input, see)
    ->  '$compilation_level'(T, Level)
    ;   '$compilation_level'(T, Level0),
	Level is Level0+1
    ).


%!  compiling
%
%   Is true if SWI-Prolog is generating a state or qlf file or
%   executes a `call' directive while doing this.

compiling :-
    \+ (   '$compilation_mode'(database),
	   '$directive_mode'(database)
       ).

:- meta_predicate
    '$ifcompiling'(0).

'$ifcompiling'(G) :-
    (   '$compilation_mode'(database)
    ->  true
    ;   call(G)
    ).

		/********************************
		*         READ SOURCE           *
		*********************************/

%!  '$load_msg_level'(+Action, +NestingLevel, -StartVerbose, -EndVerbose)

'$load_msg_level'(Action, Nesting, Start, Done) :-
    '$update_autoload_level'([], 0),
    !,
    current_prolog_flag(verbose_load, Type0),
    '$load_msg_compat'(Type0, Type),
    (   '$load_msg_level'(Action, Nesting, Type, Start, Done)
    ->  true
    ).
'$load_msg_level'(_, _, silent, silent).

'$load_msg_compat'(true, normal) :- !.
'$load_msg_compat'(false, silent) :- !.
'$load_msg_compat'(X, X).

'$load_msg_level'(load_file,    _, full,   informational, informational).
'$load_msg_level'(include_file, _, full,   informational, informational).
'$load_msg_level'(load_file,    _, normal, silent,        informational).
'$load_msg_level'(include_file, _, normal, silent,        silent).
'$load_msg_level'(load_file,    0, brief,  silent,        informational).
'$load_msg_level'(load_file,    _, brief,  silent,        silent).
'$load_msg_level'(include_file, _, brief,  silent,        silent).
'$load_msg_level'(load_file,    _, silent, silent,        silent).
'$load_msg_level'(include_file, _, silent, silent,        silent).

%!  '$source_term'(+From, -Read, -RLayout, -Term, -TLayout,
%!                 -Stream, +Options) is nondet.
%
%   Read Prolog terms from the  input   From.  Terms are returned on
%   backtracking. Associated resources (i.e.,   streams)  are closed
%   due to setup_call_cleanup/3.
%
%   @param From is either a term stream(Id, Stream) or a file
%          specification.
%   @param Read is the raw term as read from the input.
%   @param Term is the term after term-expansion.  If a term is
%          expanded into the empty list, this is returned too.  This
%          is required to be able to return the raw term in Read
%   @param Stream is the stream from which Read is read
%   @param Options provides additional options:
%           * encoding(Enc)
%           Encoding used to open From
%           * syntax_errors(+ErrorMode)
%           * process_comments(+Boolean)
%           * term_position(-Pos)

'$source_term'(From, Read, RLayout, Term, TLayout, Stream, Options) :-
    '$source_term'(From, Read, RLayout, Term, TLayout, Stream, [], Options),
    (   Term == end_of_file
    ->  !, fail
    ;   Term \== begin_of_file
    ).

'$source_term'(Input, _,_,_,_,_,_,_) :-
    \+ ground(Input),
    !,
    '$instantiation_error'(Input).
'$source_term'(stream(Id, In, Opts),
	       Read, RLayout, Term, TLayout, Stream, Parents, Options) :-
    !,
    '$record_included'(Parents, Id, Id, 0.0, Message),
    setup_call_cleanup(
	'$open_source'(stream(Id, In, Opts), In, State, Parents, Options),
	'$term_in_file'(In, Read, RLayout, Term, TLayout, Stream,
			[Id|Parents], Options),
	'$close_source'(State, Message)).
'$source_term'(File,
	       Read, RLayout, Term, TLayout, Stream, Parents, Options) :-
    absolute_file_name(File, Path,
		       [ file_type(prolog),
			 access(read)
		       ]),
    time_file(Path, Time),
    '$record_included'(Parents, File, Path, Time, Message),
    setup_call_cleanup(
	'$open_source'(Path, In, State, Parents, Options),
	'$term_in_file'(In, Read, RLayout, Term, TLayout, Stream,
			[Path|Parents], Options),
	'$close_source'(State, Message)).

:- thread_local
    '$load_input'/2.
:- volatile
    '$load_input'/2.
:- '$notransact'('$load_input'/2).

'$open_source'(stream(Id, In, Opts), In,
	       restore(In, StreamState, Id, Ref, Opts), Parents, _Options) :-
    !,
    '$context_type'(Parents, ContextType),
    '$push_input_context'(ContextType),
    '$prepare_load_stream'(In, Id, StreamState),
    asserta('$load_input'(stream(Id), In), Ref).
'$open_source'(Path, In, close(In, Path, Ref), Parents, Options) :-
    '$context_type'(Parents, ContextType),
    '$push_input_context'(ContextType),
    '$open_source'(Path, In, Options),
    '$set_encoding'(In, Options),
    asserta('$load_input'(Path, In), Ref).

'$context_type'([], load_file) :- !.
'$context_type'(_, include).

:- multifile prolog:open_source_hook/3.

'$open_source'(Path, In, Options) :-
    prolog:open_source_hook(Path, In, Options),
    !.
'$open_source'(Path, In, _Options) :-
    open(Path, read, In).

'$close_source'(close(In, _Id, Ref), Message) :-
    erase(Ref),
    call_cleanup(
	close(In),
	'$pop_input_context'),
    '$close_message'(Message).
'$close_source'(restore(In, StreamState, _Id, Ref, Opts), Message) :-
    erase(Ref),
    call_cleanup(
	'$restore_load_stream'(In, StreamState, Opts),
	'$pop_input_context'),
    '$close_message'(Message).

'$close_message'(message(Level, Msg)) :-
    !,
    '$print_message'(Level, Msg).
'$close_message'(_).


%!  '$term_in_file'(+In, -Read, -RLayout, -Term, -TLayout,
%!                  -Stream, +Parents, +Options) is multi.
%
%   True when Term is an expanded term from   In. Read is a raw term
%   (before term-expansion). Stream is  the   actual  stream,  which
%   starts at In, but may change due to processing included files.
%
%   @see '$source_term'/8 for details.

'$term_in_file'(In, Read, RLayout, Term, TLayout, Stream, Parents, Options) :-
    Parents \= [_,_|_],
    (   '$load_input'(_, Input)
    ->  stream_property(Input, file_name(File))
    ),
    '$set_source_location'(File, 0),
    '$expanded_term'(In,
		     begin_of_file, 0-0, Read, RLayout, Term, TLayout,
		     Stream, Parents, Options).
'$term_in_file'(In, Read, RLayout, Term, TLayout, Stream, Parents, Options) :-
    '$skip_script_line'(In, Options),
    '$read_clause_options'(Options, ReadOptions),
    '$repeat_and_read_error_mode'(ErrorMode),
      read_clause(In, Raw,
		  [ syntax_errors(ErrorMode),
		    variable_names(Bindings),
		    term_position(Pos),
		    subterm_positions(RawLayout)
		  | ReadOptions
		  ]),
      b_setval('$term_position', Pos),
      b_setval('$variable_names', Bindings),
      (   Raw == end_of_file
      ->  !,
	  (   Parents = [_,_|_]     % Included file
	  ->  fail
	  ;   '$expanded_term'(In,
			       Raw, RawLayout, Read, RLayout, Term, TLayout,
			       Stream, Parents, Options)
	  )
      ;   '$expanded_term'(In, Raw, RawLayout, Read, RLayout, Term, TLayout,
			   Stream, Parents, Options)
      ).

'$read_clause_options'([], []).
'$read_clause_options'([H|T0], List) :-
    (   '$read_clause_option'(H)
    ->  List = [H|T]
    ;   List = T
    ),
    '$read_clause_options'(T0, T).

'$read_clause_option'(syntax_errors(_)).
'$read_clause_option'(term_position(_)).
'$read_clause_option'(process_comment(_)).

%!  '$repeat_and_read_error_mode'(-Mode) is multi.
%
%   Calls repeat/1 and return the error  mode. The implemenation is like
%   this because during part of the  boot   cycle  expand.pl  is not yet
%   loaded.

'$repeat_and_read_error_mode'(Mode) :-
    (   current_predicate('$including'/0)
    ->  repeat,
	(   '$including'
	->  Mode = dec10
	;   Mode = quiet
	)
    ;   Mode = dec10,
	repeat
    ).


'$expanded_term'(In, Raw, RawLayout, Read, RLayout, Term, TLayout,
		 Stream, Parents, Options) :-
    E = error(_,_),
    catch('$expand_term'(Raw, RawLayout, Expanded, ExpandedLayout), E,
	  '$print_message_fail'(E)),
    (   Expanded \== []
    ->  '$expansion_member'(Expanded, ExpandedLayout, Term1, Layout1)
    ;   Term1 = Expanded,
	Layout1 = ExpandedLayout
    ),
    (   nonvar(Term1), Term1 = (:-Directive), nonvar(Directive)
    ->  (   Directive = include(File),
	    '$current_source_module'(Module),
	    '$valid_directive'(Module:include(File))
	->  stream_property(In, encoding(Enc)),
	    '$add_encoding'(Enc, Options, Options1),
	    '$source_term'(File, Read, RLayout, Term, TLayout,
			   Stream, Parents, Options1)
	;   Directive = encoding(Enc)
	->  set_stream(In, encoding(Enc)),
	    fail
	;   Term = Term1,
	    Stream = In,
	    Read = Raw
	)
    ;   Term = Term1,
	TLayout = Layout1,
	Stream = In,
	Read = Raw,
	RLayout = RawLayout
    ).

'$expansion_member'(Var, Layout, Var, Layout) :-
    var(Var),
    !.
'$expansion_member'([], _, _, _) :- !, fail.
'$expansion_member'(List, ListLayout, Term, Layout) :-
    is_list(List),
    !,
    (   var(ListLayout)
    ->  '$member'(Term, List)
    ;   is_list(ListLayout)
    ->  '$member_rep2'(Term, Layout, List, ListLayout)
    ;   Layout = ListLayout,
	'$member'(Term, List)
    ).
'$expansion_member'(X, Layout, X, Layout).

% pairwise member, repeating last element of the second
% list.

'$member_rep2'(H1, H2, [H1|_], [H2|_]).
'$member_rep2'(H1, H2, [_|T1], [T2]) :-
    !,
    '$member_rep2'(H1, H2, T1, [T2]).
'$member_rep2'(H1, H2, [_|T1], [_|T2]) :-
    '$member_rep2'(H1, H2, T1, T2).

%!  '$add_encoding'(+Enc, +Options0, -Options)

'$add_encoding'(Enc, Options0, Options) :-
    (   Options0 = [encoding(Enc)|_]
    ->  Options = Options0
    ;   Options = [encoding(Enc)|Options0]
    ).


:- multifile
    '$included'/4.                  % Into, Line, File, LastModified
:- dynamic
    '$included'/4.

%!  '$record_included'(+Parents, +File, +Path, +Time, -Message) is det.
%
%   Record that we included File into the   head of Parents. This is
%   troublesome when creating a QLF  file   because  this may happen
%   before we opened the QLF file (and  we   do  not yet know how to
%   open the file because we  do  not   yet  know  whether this is a
%   module file or not).
%
%   I think that the only sensible  solution   is  to have a special
%   statement for this, that may appear  both inside and outside QLF
%   `parts'.

'$record_included'([Parent|Parents], File, Path, Time,
		   message(DoneMsgLevel,
			   include_file(done(Level, file(File, Path))))) :-
    source_location(SrcFile, Line),
    !,
    '$compilation_level'(Level),
    '$load_msg_level'(include_file, Level, StartMsgLevel, DoneMsgLevel),
    '$print_message'(StartMsgLevel,
		     include_file(start(Level,
					file(File, Path)))),
    '$last'([Parent|Parents], Owner),
    (   (   '$compilation_mode'(database)
	;   '$qlf_current_source'(Owner)
	)
    ->  '$store_admin_clause'(
	    system:'$included'(Parent, Line, Path, Time),
	    _, Owner, SrcFile:Line)
    ;   '$qlf_include'(Owner, Parent, Line, Path, Time)
    ).
'$record_included'(_, _, _, _, true).

%!  '$master_file'(+File, -MasterFile)
%
%   Find the primary load file from included files.

'$master_file'(File, MasterFile) :-
    '$included'(MasterFile0, _Line, File, _Time),
    !,
    '$master_file'(MasterFile0, MasterFile).
'$master_file'(File, File).


'$skip_script_line'(_In, Options) :-
    '$option'(check_script(false), Options),
    !.
'$skip_script_line'(In, _Options) :-
    (   peek_char(In, #)
    ->  skip(In, 10)
    ;   true
    ).

'$set_encoding'(Stream, Options) :-
    '$option'(encoding(Enc), Options),
    !,
    Enc \== default,
    set_stream(Stream, encoding(Enc)).
'$set_encoding'(_, _).


'$prepare_load_stream'(In, Id, state(HasName,HasPos)) :-
    (   stream_property(In, file_name(_))
    ->  HasName = true,
	(   stream_property(In, position(_))
	->  HasPos = true
	;   HasPos = false,
	    set_stream(In, record_position(true))
	)
    ;   HasName = false,
	set_stream(In, file_name(Id)),
	(   stream_property(In, position(_))
	->  HasPos = true
	;   HasPos = false,
	    set_stream(In, record_position(true))
	)
    ).

'$restore_load_stream'(In, _State, Options) :-
    memberchk(close(true), Options),
    !,
    close(In).
'$restore_load_stream'(In, state(HasName, HasPos), _Options) :-
    (   HasName == false
    ->  set_stream(In, file_name(''))
    ;   true
    ),
    (   HasPos == false
    ->  set_stream(In, record_position(false))
    ;   true
    ).


		 /*******************************
		 *          DERIVED FILES       *
		 *******************************/

:- dynamic
    '$derived_source_db'/3.         % Loaded, DerivedFrom, Time

'$register_derived_source'(_, '-') :- !.
'$register_derived_source'(Loaded, DerivedFrom) :-
    retractall('$derived_source_db'(Loaded, _, _)),
    time_file(DerivedFrom, Time),
    assert('$derived_source_db'(Loaded, DerivedFrom, Time)).

%       Auto-importing dynamic predicates is not very elegant and
%       leads to problems with qsave_program/[1,2]

'$derived_source'(Loaded, DerivedFrom, Time) :-
    '$derived_source_db'(Loaded, DerivedFrom, Time).


		/********************************
		*       LOAD PREDICATES         *
		*********************************/

:- meta_predicate
    ensure_loaded(:),
    [:|+],
    consult(:),
    use_module(:),
    use_module(:, +),
    reexport(:),
    reexport(:, +),
    load_files(:),
    load_files(:, +).

%!  ensure_loaded(+FileOrListOfFiles)
%
%   Load specified files, provided they where not loaded before. If the
%   file is a module file import the public predicates into the context
%   module.

ensure_loaded(Files) :-
    load_files(Files, [if(not_loaded)]).

%!  use_module(+FileOrListOfFiles)
%
%   Very similar to ensure_loaded/1, but insists on the loaded file to
%   be a module file. If the file is already imported, but the public
%   predicates are not yet imported into the context module, then do
%   so.

use_module(Files) :-
    load_files(Files, [ if(not_loaded),
			must_be_module(true)
		      ]).

%!  use_module(+File, +ImportList)
%
%   As use_module/1, but takes only one file argument and imports only
%   the specified predicates rather than all public predicates.

use_module(File, Import) :-
    load_files(File, [ if(not_loaded),
		       must_be_module(true),
		       imports(Import)
		     ]).

%!  reexport(+Files)
%
%   As use_module/1, exporting all imported predicates.

reexport(Files) :-
    load_files(Files, [ if(not_loaded),
			must_be_module(true),
			reexport(true)
		      ]).

%!  reexport(+File, +ImportList)
%
%   As use_module/1, re-exporting all imported predicates.

reexport(File, Import) :-
    load_files(File, [ if(not_loaded),
		       must_be_module(true),
		       imports(Import),
		       reexport(true)
		     ]).


[X] :-
    !,
    consult(X).
[M:F|R] :-
    consult(M:[F|R]).

consult(M:X) :-
    X == user,
    !,
    flag('$user_consult', N, N+1),
    NN is N + 1,
    atom_concat('user://', NN, Id),
    '$consult_user'(M:Id).
consult(List) :-
    load_files(List, [expand(true)]).

%!  '$consult_user'(:Id) is det.
%
%   Handle ``?- [user].``. This is a   separate  predicate, such that we
%   can easily wrap this for the browser version.

'$consult_user'(Id) :-
    load_files(Id, [stream(user_input), check_script(false), silent(false)]).

%!  load_files(:File, +Options)
%
%   Common entry for all the consult derivates.  File is the raw user
%   specified file specification, possibly tagged with the module.

load_files(Files) :-
    load_files(Files, []).
load_files(Module:Files, Options) :-
    '$must_be'(list, Options),
    '$load_files'(Files, Module, Options).

'$load_files'(X, _, _) :-
    var(X),
    !,
    '$instantiation_error'(X).
'$load_files'([], _, _) :- !.
'$load_files'(Id, Module, Options) :-   % load_files(foo, [stream(In)])
    '$option'(stream(_), Options),
    !,
    (   atom(Id)
    ->  '$load_file'(Id, Module, Options)
    ;   throw(error(type_error(atom, Id), _))
    ).
'$load_files'(List, Module, Options) :-
    List = [_|_],
    !,
    '$must_be'(list, List),
    '$load_file_list'(List, Module, Options).
'$load_files'(File, Module, Options) :-
    '$load_one_file'(File, Module, Options).

'$load_file_list'([], _, _).
'$load_file_list'([File|Rest], Module, Options) :-
    E = error(_,_),
    catch('$load_one_file'(File, Module, Options), E,
	  '$print_message'(error, E)),
    '$load_file_list'(Rest, Module, Options).


'$load_one_file'(Spec, Module, Options) :-
    atomic(Spec),
    '$option'(expand(true), Options, false),
    !,
    expand_file_name(Spec, Expanded),
    (   Expanded = [Load]
    ->  true
    ;   Load = Expanded
    ),
    '$load_files'(Load, Module, [expand(false)|Options]).
'$load_one_file'(File, Module, Options) :-
    strip_module(Module:File, Into, PlainFile),
    '$load_file'(PlainFile, Into, Options).


%!  '$noload'(+Condition, +FullFile, +Options) is semidet.
%
%   True of FullFile should _not_ be loaded.

'$noload'(true, _, _) :-
    !,
    fail.
'$noload'(_, FullFile, _Options) :-
    '$time_source_file'(FullFile, Time, system),
    float(Time),
    !.
'$noload'(not_loaded, FullFile, _) :-
    source_file(FullFile),
    !.
'$noload'(changed, Derived, _) :-
    '$derived_source'(_FullFile, Derived, LoadTime),
    time_file(Derived, Modified),
    Modified @=< LoadTime,
    !.
'$noload'(changed, FullFile, Options) :-
    '$time_source_file'(FullFile, LoadTime, user),
    '$modified_id'(FullFile, Modified, Options),
    Modified @=< LoadTime,
    !.
'$noload'(exists, File, Options) :-
    '$noload'(changed, File, Options).

%!  '$qlf_file'(+Spec, +PlFile, -LoadFile, -Mode, +Options) is det.
%
%   Determine how to load the source. LoadFile is the file to be loaded,
%   Mode is how to load it. Mode is one of
%
%     - compile
%     Normal source compilation
%     - qcompile
%     Compile from source, creating a QLF file in the process
%     - qload
%     Load from QLF file.
%     - stream
%     Load from a stream.  Content can be a source or QLF file.
%
%   @arg Spec is the original search specification
%   @arg PlFile is the resolved absolute path to the Prolog file.

'$qlf_file'(Spec, _, Spec, stream, Options) :-
    '$option'(stream(_), Options),      % stream: no choice
    !.
'$qlf_file'(Spec, FullFile, LoadFile, compile, _) :-
    '$spec_extension'(Spec, Ext),       % user explicitly specified
    (   user:prolog_file_type(Ext, qlf)
    ->  absolute_file_name(Spec, LoadFile,
                           [ file_type(qlf),
                             access(read)
                           ])
    ;   user:prolog_file_type(Ext, prolog)
    ->  LoadFile = FullFile
    ),
    !.
'$qlf_file'(_, FullFile, FullFile, compile, _) :-
    current_prolog_flag(source, true),
    access_file(FullFile, read),
    !.
'$qlf_file'(Spec, FullFile, LoadFile, Mode, Options) :-
    '$compilation_mode'(database),
    file_name_extension(Base, PlExt, FullFile),
    user:prolog_file_type(PlExt, prolog),
    user:prolog_file_type(QlfExt, qlf),
    file_name_extension(Base, QlfExt, QlfFile),
    (   access_file(QlfFile, read),
        (   '$qlf_out_of_date'(FullFile, QlfFile, Why)
	->  (   access_file(QlfFile, write)
	    ->  print_message(informational,
			      qlf(recompile(Spec, FullFile, QlfFile, Why))),
		Mode = qcompile,
		LoadFile = FullFile
	    ;   Why == old,
		(   current_prolog_flag(home, PlHome),
		    sub_atom(FullFile, 0, _, _, PlHome)
		;   sub_atom(QlfFile, 0, _, _, 'res://')
		)
	    ->  print_message(silent,
			      qlf(system_lib_out_of_date(Spec, QlfFile))),
		Mode = qload,
		LoadFile = QlfFile
	    ;   print_message(warning,
			      qlf(can_not_recompile(Spec, QlfFile, Why))),
		Mode = compile,
		LoadFile = FullFile
	    )
	;   Mode = qload,
	    LoadFile = QlfFile
	)
    ->  !
    ;   '$qlf_auto'(FullFile, QlfFile, Options)
    ->  !, Mode = qcompile,
	LoadFile = FullFile
    ).
'$qlf_file'(_, FullFile, FullFile, compile, _).

%!  '$qlf_out_of_date'(+PlFile, +QlfFile, -Why) is semidet.
%
%   True if the  QlfFile  file  is   out-of-date  because  of  Why. This
%   predicate is the negation such that we can return the reason.

'$qlf_out_of_date'(PlFile, QlfFile, Why) :-
    (   access_file(PlFile, read)
    ->  time_file(PlFile, PlTime),
	time_file(QlfFile, QlfTime),
	(   PlTime > QlfTime
	->  Why = old                   % PlFile is newer
	;   Error = error(Formal,_),
	    catch('$qlf_is_compatible'(QlfFile), Error, true),
	    nonvar(Formal)              % QlfFile is incompatible
	->  Why = Error
	;   fail                        % QlfFile is up-to-date and ok
	)
    ;   fail                            % can not read .pl; try .qlf
    ).

%!  '$qlf_auto'(+PlFile, +QlfFile, +Options) is semidet.
%
%   True if we create QlfFile using   qcompile/2. This is determined
%   by the option qcompile(QlfMode) or, if   this is not present, by
%   the prolog_flag qcompile.

:- create_prolog_flag(qcompile, false, [type(atom)]).

'$qlf_auto'(PlFile, QlfFile, Options) :-
    (   memberchk(qcompile(QlfMode), Options)
    ->  true
    ;   current_prolog_flag(qcompile, QlfMode),
	\+ '$in_system_dir'(PlFile)
    ),
    (   QlfMode == auto
    ->  true
    ;   QlfMode == large,
	size_file(PlFile, Size),
	Size > 100000
    ),
    access_file(QlfFile, write).

'$in_system_dir'(PlFile) :-
    current_prolog_flag(home, Home),
    sub_atom(PlFile, 0, _, _, Home).

'$spec_extension'(File, Ext) :-
    atom(File),
    !,
    file_name_extension(_, Ext, File).
'$spec_extension'(Spec, Ext) :-
    compound(Spec),
    arg(1, Spec, Arg),
    '$segments_to_atom'(Arg, File),
    file_name_extension(_, Ext, File).


%!  '$load_file'(+Spec, +ContextModule, +Options) is det.
%
%   Load the file Spec  into   ContextModule  controlled by Options.
%   This wrapper deals with two cases  before proceeding to the real
%   loader:
%
%       * User hooks based on prolog_load_file/2
%       * The file is already loaded.

:- dynamic
    '$resolved_source_path_db'/3.                % ?Spec, ?Dialect, ?Path
:- '$notransact'('$resolved_source_path_db'/3).

'$load_file'(File, Module, Options) :-
    '$error_count'(E0, W0),
    '$load_file_e'(File, Module, Options),
    '$error_count'(E1, W1),
    Errors is E1-E0,
    Warnings is W1-W0,
    (   Errors+Warnings =:= 0
    ->  true
    ;   '$print_message'(silent, load_file_errors(File, Errors, Warnings))
    ).

:- if(current_prolog_flag(threads, true)).
'$error_count'(Errors, Warnings) :-
    current_prolog_flag(threads, true),
    !,
    thread_self(Me),
    thread_statistics(Me, errors, Errors),
    thread_statistics(Me, warnings, Warnings).
:- endif.
'$error_count'(Errors, Warnings) :-
    statistics(errors, Errors),
    statistics(warnings, Warnings).

'$load_file_e'(File, Module, Options) :-
    \+ memberchk(stream(_), Options),
    user:prolog_load_file(Module:File, Options),
    !.
'$load_file_e'(File, Module, Options) :-
    memberchk(stream(_), Options),
    !,
    '$assert_load_context_module'(File, Module, Options),
    '$qdo_load_file'(File, File, Module, Options).
'$load_file_e'(File, Module, Options) :-
    (   '$resolved_source_path'(File, FullFile, Options)
    ->  true
    ;   '$resolve_source_path'(File, FullFile, Options)
    ),
    !,
    '$mt_load_file'(File, FullFile, Module, Options).
'$load_file_e'(_, _, _).

%!  '$resolved_source_path'(+File, -FullFile, +Options) is semidet.
%
%   True when File has already been resolved to an absolute path.

'$resolved_source_path'(File, FullFile, Options) :-
    current_prolog_flag(emulated_dialect, Dialect),
    '$resolved_source_path_db'(File, Dialect, FullFile),
    (   '$source_file_property'(FullFile, from_state, true)
    ;   '$source_file_property'(FullFile, resource, true)
    ;   '$option'(if(If), Options, true),
	'$noload'(If, FullFile, Options)
    ),
    !.

%!  '$resolve_source_path'(+File, -FullFile, +Options) is semidet.
%
%   Resolve a source file specification to   an absolute path. May throw
%   existence and other errors.  Attempts:
%
%     1. Do a regular file search
%     2. Find a known source file.  This is used if the actual file was
%        loaded from a .qlf file.
%     3. Fail silently if if(exists) is in Options
%     4. Raise a existence_error(source_sink, File)

'$resolve_source_path'(File, FullFile, _Options) :-
    absolute_file_name(File, AbsFile,
		       [ file_type(prolog),
			 access(read),
                         file_errors(fail)
		       ]),
    !,
    '$admin_file'(AbsFile, FullFile),
    '$register_resolved_source_path'(File, FullFile).
'$resolve_source_path'(File, FullFile, _Options) :-
    absolute_file_name(File, FullFile,
		       [ file_type(prolog),
                         solutions(all),
                         file_errors(fail)
		       ]),
    source_file(FullFile),
    !.
'$resolve_source_path'(_File, _FullFile, Options) :-
    '$option'(if(exists), Options),
    !,
    fail.
'$resolve_source_path'(File, _FullFile, _Options) :-
    '$existence_error'(source_sink, File).

%!  '$register_resolved_source_path'(+Spec, -FullFile) is det.
%
%   If Spec is Path(File), cache where  we   found  the  file. This both
%   avoids many lookups on the  file  system   and  avoids  that Spec is
%   resolved to different locations.

'$register_resolved_source_path'(File, FullFile) :-
    (   compound(File)
    ->  current_prolog_flag(emulated_dialect, Dialect),
	(   '$resolved_source_path_db'(File, Dialect, FullFile)
	->  true
	;   asserta('$resolved_source_path_db'(File, Dialect, FullFile))
	)
    ;   true
    ).

%!  '$translated_source'(+Old, +New) is det.
%
%   Called from loading a QLF state when source files are being renamed.

:- public '$translated_source'/2.
'$translated_source'(Old, New) :-
    forall(retract('$resolved_source_path_db'(File, Dialect, Old)),
	   assertz('$resolved_source_path_db'(File, Dialect, New))).

%!  '$register_resource_file'(+FullFile) is det.
%
%   If we load a file from a resource we   lock  it, so we never have to
%   check the modification again.

'$register_resource_file'(FullFile) :-
    (   sub_atom(FullFile, 0, _, _, 'res://'),
	\+ file_name_extension(_, qlf, FullFile)
    ->  '$set_source_file'(FullFile, resource, true)
    ;   true
    ).

%!  '$already_loaded'(+File, +FullFile, +Module, +Options) is det.
%
%   Called if File is already loaded. If  this is a module-file, the
%   module must be imported into the context  Module. If it is not a
%   module file, it must be reloaded.
%
%   @bug    A file may be associated with multiple modules.  How
%           do we find the `main export module'?  Currently there
%           is no good way to find out which module is associated
%           to the file as a result of the first :- module/2 term.

'$already_loaded'(_File, FullFile, Module, Options) :-
    '$assert_load_context_module'(FullFile, Module, Options),
    '$current_module'(LoadModules, FullFile),
    !,
    (   atom(LoadModules)
    ->  LoadModule = LoadModules
    ;   LoadModules = [LoadModule|_]
    ),
    '$import_from_loaded_module'(LoadModule, Module, Options).
'$already_loaded'(_, _, user, _) :- !.
'$already_loaded'(File, FullFile, Module, Options) :-
    (   '$load_context_module'(FullFile, Module, CtxOptions),
	'$load_ctx_options'(Options, CtxOptions)
    ->  true
    ;   '$load_file'(File, Module, [if(true)|Options])
    ).

%!  '$mt_load_file'(+File, +FullFile, +Module, +Options) is det.
%
%   Deal with multi-threaded  loading  of   files.  The  thread that
%   wishes to load the thread first will  do so, while other threads
%   will wait until the leader finished and  than act as if the file
%   is already loaded.
%
%   Synchronisation is handled using  a   message  queue that exists
%   while the file is being loaded.   This synchronisation relies on
%   the fact that thread_get_message/1 throws  an existence_error if
%   the message queue  is  destroyed.  This   is  hacky.  Events  or
%   condition variables would have made a cleaner design.

:- dynamic
    '$loading_file'/3.              % File, Queue, Thread
:- volatile
    '$loading_file'/3.
:- '$notransact'('$loading_file'/3).

:- if(current_prolog_flag(threads, true)).
'$mt_load_file'(File, FullFile, Module, Options) :-
    current_prolog_flag(threads, true),
    !,
    sig_atomic(setup_call_cleanup(
		   with_mutex('$load_file',
			      '$mt_start_load'(FullFile, Loading, Options)),
		   '$mt_do_load'(Loading, File, FullFile, Module, Options),
		   '$mt_end_load'(Loading))).
:- endif.
'$mt_load_file'(File, FullFile, Module, Options) :-
    '$option'(if(If), Options, true),
    '$noload'(If, FullFile, Options),
    !,
    '$already_loaded'(File, FullFile, Module, Options).
:- if(current_prolog_flag(threads, true)).
'$mt_load_file'(File, FullFile, Module, Options) :-
    sig_atomic('$qdo_load_file'(File, FullFile, Module, Options)).
:- else.
'$mt_load_file'(File, FullFile, Module, Options) :-
    '$qdo_load_file'(File, FullFile, Module, Options).
:- endif.

:- if(current_prolog_flag(threads, true)).
'$mt_start_load'(FullFile, queue(Queue), _) :-
    '$loading_file'(FullFile, Queue, LoadThread),
    \+ thread_self(LoadThread),
    !.
'$mt_start_load'(FullFile, already_loaded, Options) :-
    '$option'(if(If), Options, true),
    '$noload'(If, FullFile, Options),
    !.
'$mt_start_load'(FullFile, Ref, _) :-
    thread_self(Me),
    message_queue_create(Queue),
    assertz('$loading_file'(FullFile, Queue, Me), Ref).

'$mt_do_load'(queue(Queue), File, FullFile, Module, Options) :-
    !,
    catch(thread_get_message(Queue, _), error(_,_), true),
    '$already_loaded'(File, FullFile, Module, Options).
'$mt_do_load'(already_loaded, File, FullFile, Module, Options) :-
    !,
    '$already_loaded'(File, FullFile, Module, Options).
'$mt_do_load'(_Ref, File, FullFile, Module, Options) :-
    '$assert_load_context_module'(FullFile, Module, Options),
    '$qdo_load_file'(File, FullFile, Module, Options).

'$mt_end_load'(queue(_)) :- !.
'$mt_end_load'(already_loaded) :- !.
'$mt_end_load'(Ref) :-
    clause('$loading_file'(_, Queue, _), _, Ref),
    erase(Ref),
    thread_send_message(Queue, done),
    message_queue_destroy(Queue).
:- endif.

%!  '$qdo_load_file'(+Spec, +FullFile, +ContextModule, +Options) is det.
%
%   Switch to qcompile mode if requested by the option '$qlf'(+Out)

'$qdo_load_file'(File, FullFile, Module, Options) :-
    '$qdo_load_file2'(File, FullFile, Module, Action, Options),
    '$register_resource_file'(FullFile),
    '$run_initialization'(FullFile, Action, Options).

'$qdo_load_file2'(File, FullFile, Module, Action, Options) :-
    memberchk('$qlf'(QlfOut), Options),
    '$stage_file'(QlfOut, StageQlf),
    !,
    setup_call_catcher_cleanup(
	'$qstart'(StageQlf, Module, State),
	'$do_load_file'(File, FullFile, Module, Action, Options),
	Catcher,
	'$qend'(State, Catcher, StageQlf, QlfOut)).
'$qdo_load_file2'(File, FullFile, Module, Action, Options) :-
    '$do_load_file'(File, FullFile, Module, Action, Options).

'$qstart'(Qlf, Module, state(OldMode, OldModule)) :-
    '$qlf_open'(Qlf),
    '$compilation_mode'(OldMode, qlf),
    '$set_source_module'(OldModule, Module).

'$qend'(state(OldMode, OldModule), Catcher, StageQlf, QlfOut) :-
    '$set_source_module'(_, OldModule),
    '$set_compilation_mode'(OldMode),
    '$qlf_close',
    '$install_staged_file'(Catcher, StageQlf, QlfOut, warn).

'$set_source_module'(OldModule, Module) :-
    '$current_source_module'(OldModule),
    '$set_source_module'(Module).

%!  '$do_load_file'(+Spec, +FullFile, +ContextModule,
%!                  -Action, +Options) is det.
%
%   Perform the actual loading.

'$do_load_file'(File, FullFile, Module, Action, Options) :-
    '$option'(derived_from(DerivedFrom), Options, -),
    '$register_derived_source'(FullFile, DerivedFrom),
    '$qlf_file'(File, FullFile, Absolute, Mode, Options),
    (   Mode == qcompile
    ->  qcompile(Module:File, Options)
    ;   '$do_load_file_2'(File, Absolute, Module, Action, Options)
    ).

'$do_load_file_2'(File, Absolute, Module, Action, Options) :-
    '$source_file_property'(Absolute, number_of_clauses, OldClauses),
    statistics(cputime, OldTime),

    '$setup_load'(ScopedFlags, OldSandBoxed, OldVerbose, OldAutoLevel, OldXRef,
		  Options),

    '$compilation_level'(Level),
    '$load_msg_level'(load_file, Level, StartMsgLevel, DoneMsgLevel),
    '$print_message'(StartMsgLevel,
		     load_file(start(Level,
				     file(File, Absolute)))),

    (   memberchk(stream(FromStream), Options)
    ->  Input = stream
    ;   Input = source
    ),

    (   Input == stream,
	(   '$option'(format(qlf), Options, source)
	->  set_stream(FromStream, file_name(Absolute)),
	    '$qload_stream'(FromStream, Module, Action, LM, Options)
	;   '$consult_file'(stream(Absolute, FromStream, []),
			    Module, Action, LM, Options)
	)
    ->  true
    ;   Input == source,
	file_name_extension(_, Ext, Absolute),
	(   user:prolog_file_type(Ext, qlf),
	    E = error(_,_),
	    catch('$qload_file'(Absolute, Module, Action, LM, Options),
		  E,
		  print_message(warning, E))
	->  true
	;   '$consult_file'(Absolute, Module, Action, LM, Options)
	)
    ->  true
    ;   '$print_message'(error, load_file(failed(File))),
	fail
    ),

    '$import_from_loaded_module'(LM, Module, Options),

    '$source_file_property'(Absolute, number_of_clauses, NewClauses),
    statistics(cputime, Time),
    ClausesCreated is NewClauses - OldClauses,
    TimeUsed is Time - OldTime,

    '$print_message'(DoneMsgLevel,
		     load_file(done(Level,
				    file(File, Absolute),
				    Action,
				    LM,
				    TimeUsed,
				    ClausesCreated))),

    '$restore_load'(ScopedFlags, OldSandBoxed, OldVerbose, OldAutoLevel, OldXRef).

'$setup_load'(ScopedFlags, OldSandBoxed, OldVerbose, OldAutoLevel, OldXRef,
	      Options) :-
    '$save_file_scoped_flags'(ScopedFlags),
    '$set_sandboxed_load'(Options, OldSandBoxed),
    '$set_verbose_load'(Options, OldVerbose),
    '$set_optimise_load'(Options),
    '$update_autoload_level'(Options, OldAutoLevel),
    '$set_no_xref'(OldXRef).

'$restore_load'(ScopedFlags, OldSandBoxed, OldVerbose, OldAutoLevel, OldXRef) :-
    '$set_autoload_level'(OldAutoLevel),
    set_prolog_flag(xref, OldXRef),
    set_prolog_flag(verbose_load, OldVerbose),
    set_prolog_flag(sandboxed_load, OldSandBoxed),
    '$restore_file_scoped_flags'(ScopedFlags).


%!  '$save_file_scoped_flags'(-State) is det.
%!  '$restore_file_scoped_flags'(-State) is det.
%
%   Save/restore flags that are scoped to a compilation unit.

'$save_file_scoped_flags'(State) :-
    current_predicate(findall/3),          % Not when doing boot compile
    !,
    findall(SavedFlag, '$save_file_scoped_flag'(SavedFlag), State).
'$save_file_scoped_flags'([]).

'$save_file_scoped_flag'(Flag-Value) :-
    '$file_scoped_flag'(Flag, Default),
    (   current_prolog_flag(Flag, Value)
    ->  true
    ;   Value = Default
    ).

'$file_scoped_flag'(generate_debug_info, true).
'$file_scoped_flag'(optimise,            false).
'$file_scoped_flag'(xref,                false).

'$restore_file_scoped_flags'([]).
'$restore_file_scoped_flags'([Flag-Value|T]) :-
    set_prolog_flag(Flag, Value),
    '$restore_file_scoped_flags'(T).


%! '$import_from_loaded_module'(+LoadedModule, +Module, +Options) is det.
%
%   Import public predicates from LoadedModule into Module

'$import_from_loaded_module'(LoadedModule, Module, Options) :-
    LoadedModule \== Module,
    atom(LoadedModule),
    !,
    '$option'(imports(Import), Options, all),
    '$option'(reexport(Reexport), Options, false),
    '$import_list'(Module, LoadedModule, Import, Reexport).
'$import_from_loaded_module'(_, _, _).


%!  '$set_verbose_load'(+Options, -Old) is det.
%
%   Set the =verbose_load= flag according to   Options and unify Old
%   with the old value.

'$set_verbose_load'(Options, Old) :-
    current_prolog_flag(verbose_load, Old),
    (   memberchk(silent(Silent), Options)
    ->  (   '$negate'(Silent, Level0)
	->  '$load_msg_compat'(Level0, Level)
	;   Level = Silent
	),
	set_prolog_flag(verbose_load, Level)
    ;   true
    ).

'$negate'(true, false).
'$negate'(false, true).

%!  '$set_sandboxed_load'(+Options, -Old) is det.
%
%   Update the Prolog flag  =sandboxed_load=   from  Options. Old is
%   unified with the old flag.
%
%   @error permission_error(leave, sandbox, -)

'$set_sandboxed_load'(Options, Old) :-
    current_prolog_flag(sandboxed_load, Old),
    (   memberchk(sandboxed(SandBoxed), Options),
	'$enter_sandboxed'(Old, SandBoxed, New),
	New \== Old
    ->  set_prolog_flag(sandboxed_load, New)
    ;   true
    ).

'$enter_sandboxed'(Old, New, SandBoxed) :-
    (   Old == false, New == true
    ->  SandBoxed = true,
	'$ensure_loaded_library_sandbox'
    ;   Old == true, New == false
    ->  throw(error(permission_error(leave, sandbox, -), _))
    ;   SandBoxed = Old
    ).
'$enter_sandboxed'(false, true, true).

'$ensure_loaded_library_sandbox' :-
    source_file_property(library(sandbox), module(sandbox)),
    !.
'$ensure_loaded_library_sandbox' :-
    load_files(library(sandbox), [if(not_loaded), silent(true)]).

'$set_optimise_load'(Options) :-
    (   '$option'(optimise(Optimise), Options)
    ->  set_prolog_flag(optimise, Optimise)
    ;   true
    ).

'$set_no_xref'(OldXRef) :-
    (   current_prolog_flag(xref, OldXRef)
    ->  true
    ;   OldXRef = false
    ),
    set_prolog_flag(xref, false).


%!  '$update_autoload_level'(+Options, -OldLevel)
%
%   Update the '$autoload_nesting' and return the old value.

:- thread_local
    '$autoload_nesting'/1.
:- '$notransact'('$autoload_nesting'/1).

'$update_autoload_level'(Options, AutoLevel) :-
    '$option'(autoload(Autoload), Options, false),
    (   '$autoload_nesting'(CurrentLevel)
    ->  AutoLevel = CurrentLevel
    ;   AutoLevel = 0
    ),
    (   Autoload == false
    ->  true
    ;   NewLevel is AutoLevel + 1,
	'$set_autoload_level'(NewLevel)
    ).

'$set_autoload_level'(New) :-
    retractall('$autoload_nesting'(_)),
    asserta('$autoload_nesting'(New)).


%!  '$print_message'(+Level, +Term) is det.
%
%   As print_message/2, but deal with  the   fact  that  the message
%   system might not yet be loaded.

'$print_message'(Level, Term) :-
    current_predicate(system:print_message/2),
    !,
    print_message(Level, Term).
'$print_message'(warning, Term) :-
    source_location(File, Line),
    !,
    format(user_error, 'WARNING: ~w:~w: ~p~n', [File, Line, Term]).
'$print_message'(error, Term) :-
    !,
    source_location(File, Line),
    !,
    format(user_error, 'ERROR: ~w:~w: ~p~n', [File, Line, Term]).
'$print_message'(_Level, _Term).

'$print_message_fail'(E) :-
    '$print_message'(error, E),
    fail.

%!  '$consult_file'(+Path, +Module, -Action, -LoadedIn, +Options)
%
%   Called  from  '$do_load_file'/4  using  the   goal  returned  by
%   '$consult_goal'/2. This means that the  calling conventions must
%   be kept synchronous with '$qload_file'/6.

'$consult_file'(Absolute, Module, What, LM, Options) :-
    '$current_source_module'(Module),   % same module
    !,
    '$consult_file_2'(Absolute, Module, What, LM, Options).
'$consult_file'(Absolute, Module, What, LM, Options) :-
    '$set_source_module'(OldModule, Module),
    '$ifcompiling'('$qlf_start_sub_module'(Module)),
    '$consult_file_2'(Absolute, Module, What, LM, Options),
    '$ifcompiling'('$qlf_end_part'),
    '$set_source_module'(OldModule).

'$consult_file_2'(Absolute, Module, What, LM, Options) :-
    '$set_source_module'(OldModule, Module),
    '$load_id'(Absolute, Id, Modified, Options),
    '$compile_type'(What),
    '$save_lex_state'(LexState, Options),
    '$set_dialect'(Options),
    setup_call_cleanup(
	'$start_consult'(Id, Modified),
	'$load_file'(Absolute, Id, LM, Options),
	'$end_consult'(Id, LexState, OldModule)).

'$end_consult'(Id, LexState, OldModule) :-
    '$end_consult'(Id),
    '$restore_lex_state'(LexState),
    '$set_source_module'(OldModule).


:- create_prolog_flag(emulated_dialect, swi, [type(atom)]).

%!  '$save_lex_state'(-LexState, +Options) is det.

'$save_lex_state'(State, Options) :-
    memberchk(scope_settings(false), Options),
    !,
    State = (-).
'$save_lex_state'(lexstate(Style, Dialect), _) :-
    '$style_check'(Style, Style),
    current_prolog_flag(emulated_dialect, Dialect).

'$restore_lex_state'(-) :- !.
'$restore_lex_state'(lexstate(Style, Dialect)) :-
    '$style_check'(_, Style),
    set_prolog_flag(emulated_dialect, Dialect).

'$set_dialect'(Options) :-
    memberchk(dialect(Dialect), Options),
    !,
    '$expects_dialect'(Dialect).
'$set_dialect'(_).

'$load_id'(stream(Id, _, _), Id, Modified, Options) :-
    !,
    '$modified_id'(Id, Modified, Options).
'$load_id'(Id, Id, Modified, Options) :-
    '$modified_id'(Id, Modified, Options).

'$modified_id'(_, Modified, Options) :-
    '$option'(modified(Stamp), Options, Def),
    Stamp \== Def,
    !,
    Modified = Stamp.
'$modified_id'(Id, Modified, _) :-
    catch(time_file(Id, Modified),
	  error(_, _),
	  fail),
    !.
'$modified_id'(_, 0, _).


'$compile_type'(What) :-
    '$compilation_mode'(How),
    (   How == database
    ->  What = compiled
    ;   How == qlf
    ->  What = '*qcompiled*'
    ;   What = 'boot compiled'
    ).

%!  '$assert_load_context_module'(+File, -Module, -Options)
%
%   Record the module a file was loaded from (see make/0). The first
%   clause deals with loading from  another   file.  On reload, this
%   clause will be discarded by  $start_consult/1. The second clause
%   deals with reload from the toplevel.   Here  we avoid creating a
%   duplicate dynamic (i.e., not related to a source) clause.

:- dynamic
    '$load_context_module'/3.
:- multifile
    '$load_context_module'/3.
:- '$notransact'('$load_context_module'/3).

'$assert_load_context_module'(_, _, Options) :-
    memberchk(register(false), Options),
    !.
'$assert_load_context_module'(File, Module, Options) :-
    source_location(FromFile, Line),
    !,
    '$master_file'(FromFile, MasterFile),
    '$admin_file'(File, PlFile),
    '$check_load_non_module'(PlFile, Module),
    '$add_dialect'(Options, Options1),
    '$load_ctx_options'(Options1, Options2),
    '$store_admin_clause'(
	system:'$load_context_module'(PlFile, Module, Options2),
	_Layout, MasterFile, FromFile:Line).
'$assert_load_context_module'(File, Module, Options) :-
    '$admin_file'(File, PlFile),
    '$check_load_non_module'(PlFile, Module),
    '$add_dialect'(Options, Options1),
    '$load_ctx_options'(Options1, Options2),
    (   clause('$load_context_module'(PlFile, Module, _), true, Ref),
	\+ clause_property(Ref, file(_)),
	erase(Ref)
    ->  true
    ;   true
    ),
    assertz('$load_context_module'(PlFile, Module, Options2)).

%!  '$admin_file'(+File, -PlFile) is det.
%
%   Get the canonical Prolog file name in case File is a .qlf file. Note
%   that all source admin uses the Prolog file names rather than the qlf
%   file names.

'$admin_file'(QlfFile, PlFile) :-
    file_name_extension(_, qlf, QlfFile),
    '$qlf_module'(QlfFile, Info),
    get_dict(file, Info, PlFile),
    !.
'$admin_file'(File, File).

%!  '$add_dialect'(+Options0, -Options) is det.
%
%   If we are in a dialect  environment,   add  this to the load options
%   such  that  the  load  context  reflects  the  correct  options  for
%   reloading this file.

'$add_dialect'(Options0, Options) :-
    current_prolog_flag(emulated_dialect, Dialect), Dialect \== swi,
    !,
    Options = [dialect(Dialect)|Options0].
'$add_dialect'(Options, Options).

%!  '$load_ctx_options'(+Options, -CtxOptions) is det.
%
%   Select the load options that  determine   the  load semantics to
%   perform a proper reload. Delete the others.

'$load_ctx_options'(Options, CtxOptions) :-
    '$load_ctx_options2'(Options, CtxOptions0),
    sort(CtxOptions0, CtxOptions).

'$load_ctx_options2'([], []).
'$load_ctx_options2'([H|T0], [H|T]) :-
    '$load_ctx_option'(H),
    !,
    '$load_ctx_options2'(T0, T).
'$load_ctx_options2'([_|T0], T) :-
    '$load_ctx_options2'(T0, T).

'$load_ctx_option'(derived_from(_)).
'$load_ctx_option'(dialect(_)).
'$load_ctx_option'(encoding(_)).
'$load_ctx_option'(imports(_)).
'$load_ctx_option'(reexport(_)).


%!  '$check_load_non_module'(+File) is det.
%
%   Test  that  a  non-module  file  is  not  loaded  into  multiple
%   contexts.

'$check_load_non_module'(File, _) :-
    '$current_module'(_, File),
    !.          % File is a module file
'$check_load_non_module'(File, Module) :-
    '$load_context_module'(File, OldModule, _),
    Module \== OldModule,
    !,
    format(atom(Msg),
	   'Non-module file already loaded into module ~w; \c
	       trying to load into ~w',
	   [OldModule, Module]),
    throw(error(permission_error(load, source, File),
		context(load_files/2, Msg))).
'$check_load_non_module'(_, _).

%!  '$load_file'(+Path, +Id, -Module, +Options)
%
%   '$load_file'/4 does the actual loading.
%
%   state(FirstTerm:boolean,
%         Module:atom,
%         AtEnd:atom,
%         Stop:boolean,
%         Id:atom,
%         Dialect:atom)

'$load_file'(Path, Id, Module, Options) :-
    State = state(true, _, true, false, Id, -),
    (   '$source_term'(Path, _Read, _Layout, Term, Layout,
		       _Stream, Options),
	'$valid_term'(Term),
	(   arg(1, State, true)
	->  '$first_term'(Term, Layout, Id, State, Options),
	    nb_setarg(1, State, false)
	;   '$compile_term'(Term, Layout, Id, Options)
	),
	arg(4, State, true)
    ;   '$fixup_reconsult'(Id),
	'$end_load_file'(State)
    ),
    !,
    arg(2, State, Module).

'$valid_term'(Var) :-
    var(Var),
    !,
    print_message(error, error(instantiation_error, _)).
'$valid_term'(Term) :-
    Term \== [].

'$end_load_file'(State) :-
    arg(1, State, true),           % empty file
    !,
    nb_setarg(2, State, Module),
    arg(5, State, Id),
    '$current_source_module'(Module),
    '$ifcompiling'('$qlf_start_file'(Id)),
    '$ifcompiling'('$qlf_end_part').
'$end_load_file'(State) :-
    arg(3, State, End),
    '$end_load_file'(End, State).

'$end_load_file'(true, _).
'$end_load_file'(end_module, State) :-
    arg(2, State, Module),
    '$check_export'(Module),
    '$ifcompiling'('$qlf_end_part').
'$end_load_file'(end_non_module, _State) :-
    '$ifcompiling'('$qlf_end_part').


'$first_term'(?-(Directive), Layout, Id, State, Options) :-
    !,
    '$first_term'(:-(Directive), Layout, Id, State, Options).
'$first_term'(:-(Directive), _Layout, Id, State, Options) :-
    nonvar(Directive),
    (   (   Directive = module(Name, Public)
	->  Imports = []
	;   Directive = module(Name, Public, Imports)
	)
    ->  !,
	'$module_name'(Name, Id, Module, Options),
	'$start_module'(Module, Public, State, Options),
	'$module3'(Imports)
    ;   Directive = expects_dialect(Dialect)
    ->  !,
	'$set_dialect'(Dialect, State),
	fail                        % Still consider next term as first
    ).
'$first_term'(Term, Layout, Id, State, Options) :-
    '$start_non_module'(Id, Term, State, Options),
    '$compile_term'(Term, Layout, Id, Options).

%!  '$compile_term'(+Term, +Layout, +SrcId, +Options) is det.
%!  '$compile_term'(+Term, +Layout, +SrcId, +SrcLoc, +Options) is det.
%
%   Distinguish between directives and normal clauses.

'$compile_term'(Term, Layout, SrcId, Options) :-
    '$compile_term'(Term, Layout, SrcId, -, Options).

'$compile_term'(Var, _Layout, _Id, _SrcLoc, _Options) :-
    var(Var),
    !,
    '$instantiation_error'(Var).
'$compile_term'((?-Directive), _Layout, Id, _SrcLoc, Options) :-
    !,
    '$execute_directive'(Directive, Id, Options).
'$compile_term'((:-Directive), _Layout, Id, _SrcLoc, Options) :-
    !,
    '$execute_directive'(Directive, Id, Options).
'$compile_term'('$source_location'(File, Line):Term,
		Layout, Id, _SrcLoc, Options) :-
    !,
    '$compile_term'(Term, Layout, Id, File:Line, Options).
'$compile_term'(Clause, Layout, Id, SrcLoc, _Options) :-
    E = error(_,_),
    catch('$store_clause'(Clause, Layout, Id, SrcLoc), E,
	  '$print_message'(error, E)).

'$start_non_module'(_Id, Term, _State, Options) :-
    '$option'(must_be_module(true), Options, false),
    !,
    '$domain_error'(module_header, Term).
'$start_non_module'(Id, _Term, State, _Options) :-
    '$current_source_module'(Module),
    '$ifcompiling'('$qlf_start_file'(Id)),
    '$qset_dialect'(State),
    nb_setarg(2, State, Module),
    nb_setarg(3, State, end_non_module).

%!  '$set_dialect'(+Dialect, +State)
%
%   Sets the expected dialect. This is difficult if we are compiling
%   a .qlf file using qcompile/1 because   the file is already open,
%   while we are looking for the first term to decide wether this is
%   a module or not. We save the   dialect  and set it after opening
%   the file or module.
%
%   Note that expects_dialect/1 itself may   be  autoloaded from the
%   library.

'$set_dialect'(Dialect, State) :-
    '$compilation_mode'(qlf, database),
    !,
    '$expects_dialect'(Dialect),
    '$compilation_mode'(_, qlf),
    nb_setarg(6, State, Dialect).
'$set_dialect'(Dialect, _) :-
    '$expects_dialect'(Dialect).

'$qset_dialect'(State) :-
    '$compilation_mode'(qlf),
    arg(6, State, Dialect), Dialect \== (-),
    !,
    '$add_directive_wic'('$expects_dialect'(Dialect)).
'$qset_dialect'(_).

'$expects_dialect'(Dialect) :-
    Dialect == swi,
    !,
    set_prolog_flag(emulated_dialect, Dialect).
'$expects_dialect'(Dialect) :-
    current_predicate(expects_dialect/1),
    !,
    expects_dialect(Dialect).
'$expects_dialect'(Dialect) :-
    use_module(library(dialect), [expects_dialect/1]),
    expects_dialect(Dialect).


		 /*******************************
		 *           MODULES            *
		 *******************************/

'$start_module'(Module, _Public, State, _Options) :-
    '$current_module'(Module, OldFile),
    source_location(File, _Line),
    OldFile \== File, OldFile \== [],
    same_file(OldFile, File),
    !,
    nb_setarg(2, State, Module),
    nb_setarg(4, State, true).      % Stop processing
'$start_module'(Module, Public, State, Options) :-
    arg(5, State, File),
    nb_setarg(2, State, Module),
    source_location(_File, Line),
    '$option'(redefine_module(Action), Options, false),
    '$module_class'(File, Class, Super),
    '$reset_dialect'(File, Class),
    '$redefine_module'(Module, File, Action),
    '$declare_module'(Module, Class, Super, File, Line, false),
    '$export_list'(Public, Module, Ops),
    '$ifcompiling'('$qlf_start_module'(Module)),
    '$export_ops'(Ops, Module, File),
    '$qset_dialect'(State),
    nb_setarg(3, State, end_module).

%!  '$reset_dialect'(+File, +Class) is det.
%
%   Load .pl files from the SWI-Prolog distribution _always_ in
%   `swi` dialect.

'$reset_dialect'(File, library) :-
    file_name_extension(_, pl, File),
    !,
    set_prolog_flag(emulated_dialect, swi).
'$reset_dialect'(_, _).


%!  '$module3'(+Spec) is det.
%
%   Handle the 3th argument of a module declartion.

'$module3'(Var) :-
    var(Var),
    !,
    '$instantiation_error'(Var).
'$module3'([]) :- !.
'$module3'([H|T]) :-
    !,
    '$module3'(H),
    '$module3'(T).
'$module3'(Id) :-
    use_module(library(dialect/Id)).

%!  '$module_name'(?Name, +Id, -Module, +Options) is semidet.
%
%   Determine the module name.  There are some cases:
%
%     - Option module(Module) is given.  In that case, use this
%       module and if Module is the load context, ignore the module
%       header.
%     - The initial name is unbound.  Use the base name of the
%       source identifier (normally the file name).  Compatibility
%       to Ciao.  This might change; I think it is wiser to use
%       the full unique source identifier.

'$module_name'(_, _, Module, Options) :-
    '$option'(module(Module), Options),
    !,
    '$current_source_module'(Context),
    Context \== Module.                     % cause '$first_term'/5 to fail.
'$module_name'(Var, Id, Module, Options) :-
    var(Var),
    !,
    file_base_name(Id, File),
    file_name_extension(Var, _, File),
    '$module_name'(Var, Id, Module, Options).
'$module_name'(Reserved, _, _, _) :-
    '$reserved_module'(Reserved),
    !,
    throw(error(permission_error(load, module, Reserved), _)).
'$module_name'(Module, _Id, Module, _).


'$reserved_module'(system).
'$reserved_module'(user).


%!  '$redefine_module'(+Module, +File, -Redefine)

'$redefine_module'(_Module, _, false) :- !.
'$redefine_module'(Module, File, true) :-
    !,
    (   module_property(Module, file(OldFile)),
	File \== OldFile
    ->  unload_file(OldFile)
    ;   true
    ).
'$redefine_module'(Module, File, ask) :-
    (   stream_property(user_input, tty(true)),
	module_property(Module, file(OldFile)),
	File \== OldFile,
	'$rdef_response'(Module, OldFile, File, true)
    ->  '$redefine_module'(Module, File, true)
    ;   true
    ).

'$rdef_response'(Module, OldFile, File, Ok) :-
    repeat,
    print_message(query, redefine_module(Module, OldFile, File)),
    get_single_char(Char),
    '$rdef_response'(Char, Ok0),
    !,
    Ok = Ok0.

'$rdef_response'(Char, true) :-
    memberchk(Char, `yY`),
    format(user_error, 'yes~n', []).
'$rdef_response'(Char, false) :-
    memberchk(Char, `nN`),
    format(user_error, 'no~n', []).
'$rdef_response'(Char, _) :-
    memberchk(Char, `a`),
    format(user_error, 'abort~n', []),
    abort.
'$rdef_response'(_, _) :-
    print_message(help, redefine_module_reply),
    fail.


%!  '$module_class'(+File, -Class, -Super) is det.
%
%   Determine  the  file  class  and  initial  module  from  which  File
%   inherits. All boot and library modules  as   well  as  the -F script
%   files inherit from `system`, while all   normal user modules inherit
%   from `user`.

'$module_class'(File, Class, system) :-
    current_prolog_flag(home, Home),
    sub_atom(File, 0, Len, _, Home),
    (   sub_atom(File, Len, _, _, '/boot/')
    ->  !, Class = system
    ;   '$lib_prefix'(Prefix),
	sub_atom(File, Len, _, _, Prefix)
    ->  !, Class = library
    ;   file_directory_name(File, Home),
	file_name_extension(_, rc, File)
    ->  !, Class = library
    ).
'$module_class'(_, user, user).

'$lib_prefix'('/library').
'$lib_prefix'('/xpce/prolog/').

'$check_export'(Module) :-
    '$undefined_export'(Module, UndefList),
    (   '$member'(Undef, UndefList),
	strip_module(Undef, _, Local),
	print_message(error,
		      undefined_export(Module, Local)),
	fail
    ;   true
    ).


%!  '$import_list'(+TargetModule, +FromModule, +Import, +Reexport) is det.
%
%   Import from FromModule to TargetModule. Import  is one of `all`,
%   a list of optionally  mapped  predicate   indicators  or  a term
%   except(Import).
%
%   @arg Reexport is a bool asking to re-export our imports or not.

'$import_list'(_, _, Var, _) :-
    var(Var),
    !,
    throw(error(instantitation_error, _)).
'$import_list'(Target, Source, all, Reexport) :-
    !,
    '$exported_ops'(Source, Import, Predicates),
    '$module_property'(Source, exports(Predicates)),
    '$import_all'(Import, Target, Source, Reexport, weak).
'$import_list'(Target, Source, except(Spec), Reexport) :-
    !,
    '$exported_ops'(Source, Export, Predicates),
    '$module_property'(Source, exports(Predicates)),
    (   is_list(Spec)
    ->  true
    ;   throw(error(type_error(list, Spec), _))
    ),
    '$import_except'(Spec, Source, Export, Import),
    '$import_all'(Import, Target, Source, Reexport, weak).
'$import_list'(Target, Source, Import, Reexport) :-
    is_list(Import),
    !,
    '$exported_ops'(Source, Ops, []),
    '$expand_ops'(Import, Ops, Import1),
    '$import_all'(Import1, Target, Source, Reexport, strong).
'$import_list'(_, _, Import, _) :-
    '$type_error'(import_specifier, Import).

'$expand_ops'([], _, []).
'$expand_ops'([H|T0], Ops, Imports) :-
    nonvar(H), H = op(_,_,_),
    !,
    '$include'('$can_unify'(H), Ops, Ops1),
    '$append'(Ops1, T1, Imports),
    '$expand_ops'(T0, Ops, T1).
'$expand_ops'([H|T0], Ops, [H|T1]) :-
    '$expand_ops'(T0, Ops, T1).


'$import_except'([], _, List, List).
'$import_except'([H|T], Source, List0, List) :-
    '$import_except_1'(H, Source, List0, List1),
    '$import_except'(T, Source, List1, List).

'$import_except_1'(Var, _, _, _) :-
    var(Var),
    !,
    '$instantiation_error'(Var).
'$import_except_1'(PI as N, _, List0, List) :-
    '$pi'(PI), atom(N),
    !,
    '$canonical_pi'(PI, CPI),
    '$import_as'(CPI, N, List0, List).
'$import_except_1'(op(P,A,N), _, List0, List) :-
    !,
    '$remove_ops'(List0, op(P,A,N), List).
'$import_except_1'(PI, Source, List0, List) :-
    '$pi'(PI),
    !,
    '$canonical_pi'(PI, CPI),
    (   '$select'(P, List0, List),
        '$canonical_pi'(CPI, P)
    ->  true
    ;   print_message(warning,
                      error(existence_error(export, PI, module(Source)), _)),
        List = List0
    ).
'$import_except_1'(Except, _, _, _) :-
    '$type_error'(import_specifier, Except).

'$import_as'(CPI, N, [PI2|T], [CPI as N|T]) :-
    '$canonical_pi'(PI2, CPI),
    !.
'$import_as'(PI, N, [H|T0], [H|T]) :-
    !,
    '$import_as'(PI, N, T0, T).
'$import_as'(PI, _, _, _) :-
    '$existence_error'(export, PI).

'$pi'(N/A) :- atom(N), integer(A), !.
'$pi'(N//A) :- atom(N), integer(A).

'$canonical_pi'(N//A0, N/A) :-
    A is A0 + 2.
'$canonical_pi'(PI, PI).

'$remove_ops'([], _, []).
'$remove_ops'([Op|T0], Pattern, T) :-
    subsumes_term(Pattern, Op),
    !,
    '$remove_ops'(T0, Pattern, T).
'$remove_ops'([H|T0], Pattern, [H|T]) :-
    '$remove_ops'(T0, Pattern, T).


%!  '$import_all'(+Import, +Context, +Source, +Reexport, +Strength)
%
%   Import Import from Source into Context.   If Reexport is `true`, add
%   the imported material to the  exports   of  Context.  If Strength is
%   `weak`, definitions in Context overrule the   import. If `strong`, a
%   local definition is considered an error.

'$import_all'(Import, Context, Source, Reexport, Strength) :-
    '$import_all2'(Import, Context, Source, Imported, ImpOps, Strength),
    (   Reexport == true,
	(   '$list_to_conj'(Imported, Conj)
	->  export(Context:Conj),
	    '$ifcompiling'('$add_directive_wic'(export(Context:Conj)))
	;   true
	),
	source_location(File, _Line),
	'$export_ops'(ImpOps, Context, File)
    ;   true
    ).

%!  '$import_all2'(+Imports, +Context, +Source, -Imported, -ImpOps, +Strength)

'$import_all2'([], _, _, [], [], _).
'$import_all2'([PI as NewName|Rest], Context, Source,
	       [NewName/Arity|Imported], ImpOps, Strength) :-
    !,
    '$canonical_pi'(PI, Name/Arity),
    length(Args, Arity),
    Head =.. [Name|Args],
    NewHead =.. [NewName|Args],
    (   '$get_predicate_attribute'(Source:Head, meta_predicate, Meta)
    ->  Meta =.. [Name|MetaArgs],
        NewMeta =.. [NewName|MetaArgs],
        meta_predicate(Context:NewMeta)
    ;   '$get_predicate_attribute'(Source:Head, transparent, 1)
    ->  '$set_predicate_attribute'(Context:NewHead, transparent, true)
    ;   true
    ),
    (   source_location(File, Line)
    ->  E = error(_,_),
	catch('$store_admin_clause'((NewHead :- Source:Head),
				    _Layout, File, File:Line),
	      E, '$print_message'(error, E))
    ;   assertz((NewHead :- !, Source:Head)) % ! avoids problems with
    ),                                       % duplicate load
    '$import_all2'(Rest, Context, Source, Imported, ImpOps, Strength).
'$import_all2'([op(P,A,N)|Rest], Context, Source, Imported,
	       [op(P,A,N)|ImpOps], Strength) :-
    !,
    '$import_ops'(Context, Source, op(P,A,N)),
    '$import_all2'(Rest, Context, Source, Imported, ImpOps, Strength).
'$import_all2'([Pred|Rest], Context, Source, [Pred|Imported], ImpOps, Strength) :-
    Error = error(_,_),
    catch(Context:'$import'(Source:Pred, Strength), Error,
	  print_message(error, Error)),
    '$ifcompiling'('$import_wic'(Source, Pred, Strength)),
    '$import_all2'(Rest, Context, Source, Imported, ImpOps, Strength).


'$list_to_conj'([One], One) :- !.
'$list_to_conj'([H|T], (H,Rest)) :-
    '$list_to_conj'(T, Rest).

%!  '$exported_ops'(+Module, -Ops, ?Tail) is det.
%
%   Ops is a list of op(P,A,N) terms representing the operators
%   exported from Module.

'$exported_ops'(Module, Ops, Tail) :-
    '$c_current_predicate'(_, Module:'$exported_op'(_,_,_)),
    !,
    findall(op(P,A,N), Module:'$exported_op'(P,A,N), Ops, Tail).
'$exported_ops'(_, Ops, Ops).

'$exported_op'(Module, P, A, N) :-
    '$c_current_predicate'(_, Module:'$exported_op'(_,_,_)),
    Module:'$exported_op'(P, A, N).

%!  '$import_ops'(+Target, +Source, +Pattern)
%
%   Import the operators export from Source into the module table of
%   Target.  We only import operators that unify with Pattern.

'$import_ops'(To, From, Pattern) :-
    ground(Pattern),
    !,
    Pattern = op(P,A,N),
    op(P,A,To:N),
    (   '$exported_op'(From, P, A, N)
    ->  true
    ;   print_message(warning, no_exported_op(From, Pattern))
    ).
'$import_ops'(To, From, Pattern) :-
    (   '$exported_op'(From, Pri, Assoc, Name),
	Pattern = op(Pri, Assoc, Name),
	op(Pri, Assoc, To:Name),
	fail
    ;   true
    ).


%!  '$export_list'(+Declarations, +Module, -Ops)
%
%   Handle the export list of the module declaration for Module
%   associated to File.

'$export_list'(Decls, Module, Ops) :-
    is_list(Decls),
    !,
    '$do_export_list'(Decls, Module, Ops).
'$export_list'(Decls, _, _) :-
    var(Decls),
    throw(error(instantiation_error, _)).
'$export_list'(Decls, _, _) :-
    throw(error(type_error(list, Decls), _)).

'$do_export_list'([], _, []) :- !.
'$do_export_list'([H|T], Module, Ops) :-
    !,
    E = error(_,_),
    catch('$export1'(H, Module, Ops, Ops1),
	  E, ('$print_message'(error, E), Ops = Ops1)),
    '$do_export_list'(T, Module, Ops1).

'$export1'(Var, _, _, _) :-
    var(Var),
    !,
    throw(error(instantiation_error, _)).
'$export1'(Op, _, [Op|T], T) :-
    Op = op(_,_,_),
    !.
'$export1'(PI0, Module, Ops, Ops) :-
    strip_module(Module:PI0, M, PI),
    (   PI = (_//_)
    ->  non_terminal(M:PI)
    ;   true
    ),
    export(M:PI).

'$export_ops'([op(Pri, Assoc, Name)|T], Module, File) :-
    E = error(_,_),
    catch(( '$execute_directive'(op(Pri, Assoc, Module:Name), File, []),
	    '$export_op'(Pri, Assoc, Name, Module, File)
	  ),
	  E, '$print_message'(error, E)),
    '$export_ops'(T, Module, File).
'$export_ops'([], _, _).

'$export_op'(Pri, Assoc, Name, Module, File) :-
    (   '$get_predicate_attribute'(Module:'$exported_op'(_,_,_), defined, 1)
    ->  true
    ;   '$execute_directive'(discontiguous(Module:'$exported_op'/3), File, [])
    ),
    '$store_admin_clause'('$exported_op'(Pri, Assoc, Name), _Layout, File, -).

%!  '$execute_directive'(:Goal, +File, +Options) is det.
%
%   Execute the argument of :- or ?- while loading a file.

'$execute_directive'(Var, _F, _Options) :-
    var(Var),
    '$instantiation_error'(Var).
'$execute_directive'(encoding(Encoding), _F, _Options) :-
    !,
    (   '$load_input'(_F, S)
    ->  set_stream(S, encoding(Encoding))
    ).
'$execute_directive'(Goal, _, Options) :-
    \+ '$compilation_mode'(database),
    !,
    '$add_directive_wic2'(Goal, Type, Options),
    (   Type == call                % suspend compiling into .qlf file
    ->  '$compilation_mode'(Old, database),
	setup_call_cleanup(
	    '$directive_mode'(OldDir, Old),
	    '$execute_directive_3'(Goal),
	    ( '$set_compilation_mode'(Old),
	      '$set_directive_mode'(OldDir)
	    ))
    ;   '$execute_directive_3'(Goal)
    ).
'$execute_directive'(Goal, _, _Options) :-
    '$execute_directive_3'(Goal).

'$execute_directive_3'(Goal) :-
    '$current_source_module'(Module),
    '$valid_directive'(Module:Goal),
    !,
    (   '$pattr_directive'(Goal, Module)
    ->  true
    ;   Term = error(_,_),
	catch(Module:Goal, Term, '$exception_in_directive'(Term))
    ->  true
    ;   '$print_message'(warning, goal_failed(directive, Module:Goal)),
	fail
    ).
'$execute_directive_3'(_).


%!  '$valid_directive'(:Directive) is det.
%
%   If   the   flag   =sandboxed_load=   is   =true=,   this   calls
%   prolog:sandbox_allowed_directive/1. This call can deny execution
%   of the directive by throwing an exception.

:- multifile prolog:sandbox_allowed_directive/1.
:- multifile prolog:sandbox_allowed_clause/1.
:- meta_predicate '$valid_directive'(:).

'$valid_directive'(_) :-
    current_prolog_flag(sandboxed_load, false),
    !.
'$valid_directive'(Goal) :-
    Error = error(Formal, _),
    catch(prolog:sandbox_allowed_directive(Goal), Error, true),
    !,
    (   var(Formal)
    ->  true
    ;   print_message(error, Error),
	fail
    ).
'$valid_directive'(Goal) :-
    print_message(error,
		  error(permission_error(execute,
					 sandboxed_directive,
					 Goal), _)),
    fail.

'$exception_in_directive'(Term) :-
    '$print_message'(error, Term),
    fail.

%!  '$add_directive_wic2'(+Directive, -Type, +Options) is det.
%
%   Classify Directive as  one  of  `load`   or  `call`.  Add  a  `call`
%   directive  to  the  QLF  file.    `load`   directives  continue  the
%   compilation into the QLF file.

'$add_directive_wic2'(Goal, Type, Options) :-
    '$common_goal_type'(Goal, Type, Options),
    !,
    (   Type == load
    ->  true
    ;   '$current_source_module'(Module),
	'$add_directive_wic'(Module:Goal)
    ).
'$add_directive_wic2'(Goal, _, _) :-
    (   '$compilation_mode'(qlf)    % no problem for qlf files
    ->  true
    ;   print_message(error, mixed_directive(Goal))
    ).

%!  '$common_goal_type'(+Directive, -Type, +Options) is semidet.
%
%   True when _all_ subgoals of Directive   must be handled using `load`
%   or `call`.

'$common_goal_type'((A,B), Type, Options) :-
    !,
    '$common_goal_type'(A, Type, Options),
    '$common_goal_type'(B, Type, Options).
'$common_goal_type'((A;B), Type, Options) :-
    !,
    '$common_goal_type'(A, Type, Options),
    '$common_goal_type'(B, Type, Options).
'$common_goal_type'((A->B), Type, Options) :-
    !,
    '$common_goal_type'(A, Type, Options),
    '$common_goal_type'(B, Type, Options).
'$common_goal_type'(Goal, Type, Options) :-
    '$goal_type'(Goal, Type, Options).

'$goal_type'(Goal, Type, Options) :-
    (   '$load_goal'(Goal, Options)
    ->  Type = load
    ;   Type = call
    ).

:- thread_local
    '$qlf':qinclude/1.

'$load_goal'([_|_], _).
'$load_goal'(consult(_), _).
'$load_goal'(load_files(_), _).
'$load_goal'(load_files(_,Options), _) :-
    memberchk(qcompile(QlfMode), Options),
    '$qlf_part_mode'(QlfMode).
'$load_goal'(ensure_loaded(_), _) :- '$compilation_mode'(wic).
'$load_goal'(use_module(_), _)    :- '$compilation_mode'(wic).
'$load_goal'(use_module(_, _), _) :- '$compilation_mode'(wic).
'$load_goal'(reexport(_), _)      :- '$compilation_mode'(wic).
'$load_goal'(reexport(_, _), _)   :- '$compilation_mode'(wic).
'$load_goal'(Goal, _Options) :-
    '$qlf':qinclude(user),
    '$load_goal_file'(Goal, File),
    '$all_user_files'(File).


'$load_goal_file'(load_files(F), F).
'$load_goal_file'(load_files(F, _), F).
'$load_goal_file'(ensure_loaded(F), F).
'$load_goal_file'(use_module(F), F).
'$load_goal_file'(use_module(F, _), F).
'$load_goal_file'(reexport(F), F).
'$load_goal_file'(reexport(F, _), F).

'$all_user_files'([]) :-
    !.
'$all_user_files'([H|T]) :-
    !,
    '$is_user_file'(H),
    '$all_user_files'(T).
'$all_user_files'(F) :-
    ground(F),
    '$is_user_file'(F).

'$is_user_file'(File) :-
    absolute_file_name(File, Path,
		       [ file_type(prolog),
			 access(read)
		       ]),
    '$module_class'(Path, user, _).

'$qlf_part_mode'(part).
'$qlf_part_mode'(true).                 % compatibility


		/********************************
		*        COMPILE A CLAUSE       *
		*********************************/

%!  '$store_admin_clause'(+Clause, ?Layout, +Owner, +SrcLoc) is det.
%
%   Store a clause into the   database  for administrative purposes.
%   This bypasses sanity checking.

'$store_admin_clause'(Clause, Layout, Owner, SrcLoc) :-
    Owner \== (-),
    !,
    setup_call_cleanup(
	'$start_aux'(Owner, Context),
	'$store_admin_clause2'(Clause, Layout, Owner, SrcLoc),
	'$end_aux'(Owner, Context)).
'$store_admin_clause'(Clause, Layout, File, SrcLoc) :-
    '$store_admin_clause2'(Clause, Layout, File, SrcLoc).

'$store_admin_clause2'(Clause, _Layout, File, SrcLoc) :-
    (   '$compilation_mode'(database)
    ->  '$record_clause'(Clause, File, SrcLoc)
    ;   '$record_clause'(Clause, File, SrcLoc, Ref),
	'$qlf_assert_clause'(Ref, development)
    ).

%!  '$store_clause'(+Clause, ?Layout, +Owner, +SrcLoc) is det.
%
%   Store a clause into the database.
%
%   @arg    Owner is the file-id that owns the clause
%   @arg    SrcLoc is the file:line term where the clause
%           originates from.

'$store_clause'((_, _), _, _, _) :-
    !,
    print_message(error, cannot_redefine_comma),
    fail.
'$store_clause'((Pre => Body), _Layout, File, SrcLoc) :-
    nonvar(Pre),
    Pre = (Head,Cond),
    !,
    (   '$is_true'(Cond), current_prolog_flag(optimise, true)
    ->  '$store_clause'((Head=>Body), _Layout, File, SrcLoc)
    ;   '$store_clause'(?=>(Head,(Cond,!,Body)), _Layout, File, SrcLoc)
    ).
'$store_clause'(Clause, _Layout, File, SrcLoc) :-
    '$valid_clause'(Clause),
    !,
    (   '$compilation_mode'(database)
    ->  '$record_clause'(Clause, File, SrcLoc)
    ;   '$record_clause'(Clause, File, SrcLoc, Ref),
	'$qlf_assert_clause'(Ref, development)
    ).

'$is_true'(true)  => true.
'$is_true'((A,B)) => '$is_true'(A), '$is_true'(B).
'$is_true'(_)     => fail.

'$valid_clause'(_) :-
    current_prolog_flag(sandboxed_load, false),
    !.
'$valid_clause'(Clause) :-
    \+ '$cross_module_clause'(Clause),
    !.
'$valid_clause'(Clause) :-
    Error = error(Formal, _),
    catch(prolog:sandbox_allowed_clause(Clause), Error, true),
    !,
    (   var(Formal)
    ->  true
    ;   print_message(error, Error),
	fail
    ).
'$valid_clause'(Clause) :-
    print_message(error,
		  error(permission_error(assert,
					 sandboxed_clause,
					 Clause), _)),
    fail.

'$cross_module_clause'(Clause) :-
    '$head_module'(Clause, Module),
    \+ '$current_source_module'(Module).

'$head_module'(Var, _) :-
    var(Var), !, fail.
'$head_module'((Head :- _), Module) :-
    '$head_module'(Head, Module).
'$head_module'(Module:_, Module).

'$clause_source'('$source_location'(File,Line):Clause, Clause, File:Line) :- !.
'$clause_source'(Clause, Clause, -).

%!  '$store_clause'(+Term, +Id) is det.
%
%   This interface is used by PlDoc (and who knows).  Kept for to avoid
%   compatibility issues.

:- public
    '$store_clause'/2.

'$store_clause'(Term, Id) :-
    '$clause_source'(Term, Clause, SrcLoc),
    '$store_clause'(Clause, _, Id, SrcLoc).

%!  compile_aux_clauses(+Clauses) is det.
%
%   Compile clauses given the current  source   location  but do not
%   change  the  notion  of   the    current   procedure  such  that
%   discontiguous  warnings  are  not  issued.    The   clauses  are
%   associated with the current file and  therefore wiped out if the
%   file is reloaded.
%
%   If the cross-referencer is active, we should not (re-)assert the
%   clauses.  Actually,  we  should   make    them   known   to  the
%   cross-referencer. How do we do that?   Maybe we need a different
%   API, such as in:
%
%     ==
%     expand_term_aux(Goal, NewGoal, Clauses)
%     ==
%
%   @tbd    Deal with source code layout?

compile_aux_clauses(_Clauses) :-
    current_prolog_flag(xref, true),
    !.
compile_aux_clauses(Clauses) :-
    source_location(File, _Line),
    '$compile_aux_clauses'(Clauses, File).

'$compile_aux_clauses'(Clauses, File) :-
    setup_call_cleanup(
	'$start_aux'(File, Context),
	'$store_aux_clauses'(Clauses, File),
	'$end_aux'(File, Context)).

'$store_aux_clauses'(Clauses, File) :-
    is_list(Clauses),
    !,
    forall('$member'(C,Clauses),
	   '$compile_term'(C, _Layout, File, [])).
'$store_aux_clauses'(Clause, File) :-
    '$compile_term'(Clause, _Layout, File, []).


		 /*******************************
		 *            STAGING		*
		 *******************************/

%!  '$stage_file'(+Target, -Stage) is det.
%!  '$install_staged_file'(+Catcher, +Staged, +Target, +OnError).
%
%   Create files using _staging_, where we  first write a temporary file
%   and move it to Target if  the   file  was created successfully. This
%   provides an atomic transition, preventing  customers from reading an
%   incomplete file.

'$stage_file'(Target, Stage) :-
    file_directory_name(Target, Dir),
    file_base_name(Target, File),
    current_prolog_flag(pid, Pid),
    format(atom(Stage), '~w/.~w.~d', [Dir,File,Pid]).

'$install_staged_file'(exit, Staged, Target, error) :-
    !,
    rename_file(Staged, Target).
'$install_staged_file'(exit, Staged, Target, OnError) :-
    !,
    InstallError = error(_,_),
    catch(rename_file(Staged, Target),
	  InstallError,
	  '$install_staged_error'(OnError, InstallError, Staged, Target)).
'$install_staged_file'(_, Staged, _, _OnError) :-
    E = error(_,_),
    catch(delete_file(Staged), E, true).

'$install_staged_error'(OnError, Error, Staged, _Target) :-
    E = error(_,_),
    catch(delete_file(Staged), E, true),
    (   OnError = silent
    ->  true
    ;   OnError = fail
    ->  fail
    ;   print_message(warning, Error)
    ).


		 /*******************************
		 *             READING          *
		 *******************************/

:- multifile
    prolog:comment_hook/3.                  % hook for read_clause/3


		 /*******************************
		 *       FOREIGN INTERFACE      *
		 *******************************/

%       call-back from PL_register_foreign().  First argument is the module
%       into which the foreign predicate is loaded and second is a term
%       describing the arguments.

:- dynamic
    '$foreign_registered'/2.

		 /*******************************
		 *   TEMPORARY TERM EXPANSION   *
		 *******************************/

% Provide temporary definitions for the boot-loader.  These are replaced
% by the real thing in load.pl

:- dynamic
    '$expand_goal'/2,
    '$expand_term'/4.

'$expand_goal'(In, In).
'$expand_term'(In, Layout, In, Layout).


		 /*******************************
		 *         TYPE SUPPORT         *
		 *******************************/

'$type_error'(Type, Value) :-
    (   var(Value)
    ->  throw(error(instantiation_error, _))
    ;   throw(error(type_error(Type, Value), _))
    ).

'$domain_error'(Type, Value) :-
    throw(error(domain_error(Type, Value), _)).

'$existence_error'(Type, Object) :-
    throw(error(existence_error(Type, Object), _)).

'$existence_error'(Type, Object, In) :-
    throw(error(existence_error(Type, Object, In), _)).

'$permission_error'(Action, Type, Term) :-
    throw(error(permission_error(Action, Type, Term), _)).

'$instantiation_error'(_Var) :-
    throw(error(instantiation_error, _)).

'$uninstantiation_error'(NonVar) :-
    throw(error(uninstantiation_error(NonVar), _)).

'$must_be'(list, X) :- !,
    '$skip_list'(_, X, Tail),
    (   Tail == []
    ->  true
    ;   '$type_error'(list, Tail)
    ).
'$must_be'(options, X) :- !,
    (   '$is_options'(X)
    ->  true
    ;   '$type_error'(options, X)
    ).
'$must_be'(atom, X) :- !,
    (   atom(X)
    ->  true
    ;   '$type_error'(atom, X)
    ).
'$must_be'(integer, X) :- !,
    (   integer(X)
    ->  true
    ;   '$type_error'(integer, X)
    ).
'$must_be'(between(Low,High), X) :- !,
    (   integer(X)
    ->  (   between(Low, High, X)
	->  true
	;   '$domain_error'(between(Low,High), X)
	)
    ;   '$type_error'(integer, X)
    ).
'$must_be'(callable, X) :- !,
    (   callable(X)
    ->  true
    ;   '$type_error'(callable, X)
    ).
'$must_be'(acyclic, X) :- !,
    (   acyclic_term(X)
    ->  true
    ;   '$domain_error'(acyclic_term, X)
    ).
'$must_be'(oneof(Type, Domain, List), X) :- !,
    '$must_be'(Type, X),
    (   memberchk(X, List)
    ->  true
    ;   '$domain_error'(Domain, X)
    ).
'$must_be'(boolean, X) :- !,
    (   (X == true ; X == false)
    ->  true
    ;   '$type_error'(boolean, X)
    ).
'$must_be'(ground, X) :- !,
    (   ground(X)
    ->  true
    ;   '$instantiation_error'(X)
    ).
'$must_be'(filespec, X) :- !,
    (   (   atom(X)
	;   string(X)
	;   compound(X),
	    compound_name_arity(X, _, 1)
	)
    ->  true
    ;   '$type_error'(filespec, X)
    ).

% Use for debugging
%'$must_be'(Type, _X) :- format('Unknown $must_be type: ~q~n', [Type]).


		/********************************
		*       LIST PROCESSING         *
		*********************************/

'$member'(El, [H|T]) :-
    '$member_'(T, El, H).

'$member_'(_, El, El).
'$member_'([H|T], El, _) :-
    '$member_'(T, El, H).

'$append'([], L, L).
'$append'([H|T], L, [H|R]) :-
    '$append'(T, L, R).

'$append'(ListOfLists, List) :-
    '$must_be'(list, ListOfLists),
    '$append_'(ListOfLists, List).

'$append_'([], []).
'$append_'([L|Ls], As) :-
    '$append'(L, Ws, As),
    '$append_'(Ls, Ws).

'$select'(X, [X|Tail], Tail).
'$select'(Elem, [Head|Tail], [Head|Rest]) :-
    '$select'(Elem, Tail, Rest).

'$reverse'(L1, L2) :-
    '$reverse'(L1, [], L2).

'$reverse'([], List, List).
'$reverse'([Head|List1], List2, List3) :-
    '$reverse'(List1, [Head|List2], List3).

'$delete'([], _, []) :- !.
'$delete'([Elem|Tail], Elem, Result) :-
    !,
    '$delete'(Tail, Elem, Result).
'$delete'([Head|Tail], Elem, [Head|Rest]) :-
    '$delete'(Tail, Elem, Rest).

'$last'([H|T], Last) :-
    '$last'(T, H, Last).

'$last'([], Last, Last).
'$last'([H|T], _, Last) :-
    '$last'(T, H, Last).

:- meta_predicate '$include'(1,+,-).
'$include'(_, [], []).
'$include'(G, [H|T0], L) :-
    (   call(G,H)
    ->  L = [H|T]
    ;   T = L
    ),
    '$include'(G, T0, T).

'$can_unify'(A, B) :-
    \+ A \= B.

%!  length(?List, ?N)
%
%   Is true when N is the length of List.

:- '$iso'((length/2)).

length(List, Length) :-
    var(Length),
    !,
    '$skip_list'(Length0, List, Tail),
    (   Tail == []
    ->  Length = Length0                    % +,-
    ;   var(Tail)
    ->  Tail \== Length,                    % avoid length(L,L)
	'$length3'(Tail, Length, Length0)   % -,-
    ;   throw(error(type_error(list, List),
		    context(length/2, _)))
    ).
length(List, Length) :-
    integer(Length),
    Length >= 0,
    !,
    '$skip_list'(Length0, List, Tail),
    (   Tail == []                          % proper list
    ->  Length = Length0
    ;   var(Tail)
    ->  Extra is Length-Length0,
	'$length'(Tail, Extra)
    ;   throw(error(type_error(list, List),
		    context(length/2, _)))
    ).
length(_, Length) :-
    integer(Length),
    !,
    throw(error(domain_error(not_less_than_zero, Length),
		context(length/2, _))).
length(_, Length) :-
    throw(error(type_error(integer, Length),
		context(length/2, _))).

'$length3'([], N, N).
'$length3'([_|List], N, N0) :-
    N1 is N0+1,
    '$length3'(List, N, N1).


		 /*******************************
		 *       OPTION PROCESSING      *
		 *******************************/

%!  '$is_options'(@Term) is semidet.
%
%   True if Term looks like it provides options.

'$is_options'(Map) :-
    is_dict(Map, _),
    !.
'$is_options'(List) :-
    is_list(List),
    (   List == []
    ->  true
    ;   List = [H|_],
	'$is_option'(H, _, _)
    ).

'$is_option'(Var, _, _) :-
    var(Var), !, fail.
'$is_option'(F, Name, Value) :-
    functor(F, _, 1),
    !,
    F =.. [Name,Value].
'$is_option'(Name=Value, Name, Value).

%!  '$option'(?Opt, +Options) is semidet.

'$option'(Opt, Options) :-
    is_dict(Options),
    !,
    [Opt] :< Options.
'$option'(Opt, Options) :-
    memberchk(Opt, Options).

%!  '$option'(?Opt, +Options, +Default) is det.

'$option'(Term, Options, Default) :-
    arg(1, Term, Value),
    functor(Term, Name, 1),
    (   is_dict(Options)
    ->  (   get_dict(Name, Options, GVal)
	->  Value = GVal
	;   Value = Default
	)
    ;   functor(Gen, Name, 1),
	arg(1, Gen, GVal),
	(   memberchk(Gen, Options)
	->  Value = GVal
	;   Value = Default
	)
    ).

%!  '$select_option'(?Opt, +Options, -Rest) is semidet.
%
%   Select an option from Options.
%
%   @arg Rest is always a map.

'$select_option'(Opt, Options, Rest) :-
    '$options_dict'(Options, Dict),
    select_dict([Opt], Dict, Rest).

%!  '$merge_options'(+New, +Default, -Merged) is det.
%
%   Add/replace options specified in New.
%
%   @arg Merged is always a map.

'$merge_options'(New, Old, Merged) :-
    '$options_dict'(New, NewDict),
    '$options_dict'(Old, OldDict),
    put_dict(NewDict, OldDict, Merged).

%!  '$options_dict'(+Options, --Dict) is det.
%
%   Translate to an options dict. For   possible  duplicate keys we keep
%   the first.

'$options_dict'(Options, Dict) :-
    is_list(Options),
    !,
    '$keyed_options'(Options, Keyed),
    sort(1, @<, Keyed, UniqueKeyed),
    '$pairs_values'(UniqueKeyed, Unique),
    dict_create(Dict, _, Unique).
'$options_dict'(Dict, Dict) :-
    is_dict(Dict),
    !.
'$options_dict'(Options, _) :-
    '$domain_error'(options, Options).

'$keyed_options'([], []).
'$keyed_options'([H0|T0], [H|T]) :-
    '$keyed_option'(H0, H),
    '$keyed_options'(T0, T).

'$keyed_option'(Var, _) :-
    var(Var),
    !,
    '$instantiation_error'(Var).
'$keyed_option'(Name=Value, Name-(Name-Value)).
'$keyed_option'(NameValue, Name-(Name-Value)) :-
    compound_name_arguments(NameValue, Name, [Value]),
    !.
'$keyed_option'(Opt, _) :-
    '$domain_error'(option, Opt).


		 /*******************************
		 *   HANDLE TRACER 'L'-COMMAND  *
		 *******************************/

:- public '$prolog_list_goal'/1.

:- multifile
    user:prolog_list_goal/1.

'$prolog_list_goal'(Goal) :-
    user:prolog_list_goal(Goal),
    !.
'$prolog_list_goal'(Goal) :-
    use_module(library(listing), [listing/1]),
    @(listing(Goal), user).


		 /*******************************
		 *             HALT             *
		 *******************************/

:- '$iso'((halt/0)).

halt :-
    '$exit_code'(Code),
    (   Code == 0
    ->  true
    ;   print_message(warning, on_error(halt(1)))
    ),
    halt(Code).

%!  '$exit_code'(Code)
%
%   Determine the exit code baed on the `on_error` and `on_warning`
%   flags.  Also used by qsave_toplevel/0.

'$exit_code'(Code) :-
    (   (   current_prolog_flag(on_error, status),
	    statistics(errors, Count),
	    Count > 0
	;   current_prolog_flag(on_warning, status),
	    statistics(warnings, Count),
	    Count > 0
	)
    ->  Code = 1
    ;   Code = 0
    ).


%!  at_halt(:Goal)
%
%   Register Goal to be called if the system halts.
%
%   @tbd: get location into the error message

:- meta_predicate at_halt(0).
:- dynamic        system:term_expansion/2, '$at_halt'/2.
:- multifile      system:term_expansion/2, '$at_halt'/2.

system:term_expansion((:- at_halt(Goal)),
		      system:'$at_halt'(Module:Goal, File:Line)) :-
    \+ current_prolog_flag(xref, true),
    source_location(File, Line),
    '$current_source_module'(Module).

at_halt(Goal) :-
    asserta('$at_halt'(Goal, (-):0)).

:- public '$run_at_halt'/0.

'$run_at_halt' :-
    forall(clause('$at_halt'(Goal, Src), true, Ref),
	   ( '$call_at_halt'(Goal, Src),
	     erase(Ref)
	   )).

'$call_at_halt'(Goal, _Src) :-
    catch(Goal, E, true),
    !,
    (   var(E)
    ->  true
    ;   subsumes_term(cancel_halt(_), E)
    ->  '$print_message'(informational, E),
	fail
    ;   '$print_message'(error, E)
    ).
'$call_at_halt'(Goal, _Src) :-
    '$print_message'(warning, goal_failed(at_halt, Goal)).

%!  cancel_halt(+Reason)
%
%   This predicate may be called from   at_halt/1 handlers to cancel
%   halting the program. If  causes  halt/0   to  fail  rather  than
%   terminating the process.

cancel_halt(Reason) :-
    throw(cancel_halt(Reason)).

%!  prolog:heartbeat
%
%   Called every _N_ inferences  of  the   Prolog  flag  `heartbeat`  is
%   non-zero.

:- multifile prolog:heartbeat/0.


		/********************************
		*      LOAD OTHER MODULES       *
		*********************************/

:- meta_predicate
    '$load_wic_files'(:).

'$load_wic_files'(Files) :-
    Files = Module:_,
    '$execute_directive'('$set_source_module'(OldM, Module), [], []),
    '$save_lex_state'(LexState, []),
    '$style_check'(_, 0xC7),                % see style_name/2 in syspred.pl
    '$compilation_mode'(OldC, wic),
    consult(Files),
    '$execute_directive'('$set_source_module'(OldM), [], []),
    '$execute_directive'('$restore_lex_state'(LexState), [], []),
    '$set_compilation_mode'(OldC).


%!  '$load_additional_boot_files' is det.
%
%   Called from compileFileList() in pl-wic.c.   Gets the files from
%   "-c file ..." and loads them into the module user.

:- public '$load_additional_boot_files'/0.

'$load_additional_boot_files' :-
    current_prolog_flag(argv, Argv),
    '$get_files_argv'(Argv, Files),
    (   Files \== []
    ->  format('Loading additional boot files~n'),
	'$load_wic_files'(user:Files),
	format('additional boot files loaded~n')
    ;   true
    ).

'$get_files_argv'([], []) :- !.
'$get_files_argv'(['-c'|Files], Files) :- !.
'$get_files_argv'([_|Rest], Files) :-
    '$get_files_argv'(Rest, Files).

'$:-'(('$boot_message'('Loading Prolog startup files~n', []),
       source_location(File, _Line),
       file_directory_name(File, Dir),
       atom_concat(Dir, '/load.pl', LoadFile),
       '$load_wic_files'(system:[LoadFile]),
       (   current_prolog_flag(windows, true)
       ->  atom_concat(Dir, '/menu.pl', MenuFile),
	   '$load_wic_files'(system:[MenuFile])
       ;   true
       ),
       '$boot_message'('SWI-Prolog boot files loaded~n', []),
       '$compilation_mode'(OldC, wic),
       '$execute_directive'('$set_source_module'(user), [], []),
       '$set_compilation_mode'(OldC)
      )).
