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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  1985-2020, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9    All rights reserved.
   10
   11    Redistribution and use in source and binary forms, with or without
   12    modification, are permitted provided that the following conditions
   13    are met:
   14
   15    1. Redistributions of source code must retain the above copyright
   16       notice, this list of conditions and the following disclaimer.
   17
   18    2. Redistributions in binary form must reproduce the above copyright
   19       notice, this list of conditions and the following disclaimer in
   20       the documentation and/or other materials provided with the
   21       distribution.
   22
   23    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   24    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   25    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   26    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   27    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   28    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   29    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   30    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   31    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   33    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   34    POSSIBILITY OF SUCH DAMAGE.
   35*/
   36
   37:- module('$autoload',
   38          [ '$find_library'/5,
   39            '$in_library'/3,
   40            '$define_predicate'/1,
   41            '$update_library_index'/0,
   42            '$autoload'/1,
   43
   44            make_library_index/1,
   45            make_library_index/2,
   46            reload_library_index/0,
   47            autoload_path/1,
   48
   49            autoload/1,                         % +File
   50            autoload/2,                         % +File, +Imports
   51
   52            require/1				% +Predicates
   53          ]).   54
   55:- meta_predicate
   56    '$autoload'(:),
   57    autoload(:),
   58    autoload(:, +),
   59    require(:).   60
   61:- dynamic
   62    library_index/3,                % Head x Module x Path
   63    autoload_directories/1,         % List
   64    index_checked_at/1.             % Time
   65:- volatile
   66    library_index/3,
   67    autoload_directories/1,
   68    index_checked_at/1.   69
   70user:file_search_path(autoload, swi(library)).
   71user:file_search_path(autoload, pce(prolog/lib)).
   72user:file_search_path(autoload, app_config(lib)).
 $find_library(+Module, +Name, +Arity, -LoadModule, -Library) is semidet
Locate a predicate in the library. Name and arity are the name and arity of the predicate searched for. `Module' is the preferred target module. The return values are the full path name (excluding extension) of the library and module declared in that file.
   83'$find_library'(Module, Name, Arity, LoadModule, Library) :-
   84    load_library_index(Name, Arity),
   85    functor(Head, Name, Arity),
   86    (   library_index(Head, Module, Library),
   87        LoadModule = Module
   88    ;   library_index(Head, LoadModule, Library)
   89    ),
   90    !.
 $in_library(+Name, +Arity, -Path) is semidet
$in_library(-Name, -Arity, -Path) is nondet
Is true if Name/Arity is in the autoload libraries.
   97'$in_library'(Name, Arity, Path) :-
   98    atom(Name), integer(Arity),
   99    !,
  100    load_library_index(Name, Arity),
  101    functor(Head, Name, Arity),
  102    library_index(Head, _, Path).
  103'$in_library'(Name, Arity, Path) :-
  104    load_library_index(Name, Arity),
  105    library_index(Head, _, Path),
  106    functor(Head, Name, Arity).
 $define_predicate(:Head)
Make sure PredInd can be called. First test if the predicate is defined. If not, invoke the autoloader.
  113:- meta_predicate
  114    '$define_predicate'(:).  115
  116'$define_predicate'(Head) :-
  117    '$defined_predicate'(Head),
  118    !.
  119'$define_predicate'(Term) :-
  120    Term = Module:Head,
  121    (   compound(Head)
  122    ->  compound_name_arity(Head, Name, Arity)
  123    ;   Name = Head, Arity = 0
  124    ),
  125    '$undefined_procedure'(Module, Name, Arity, retry).
  126
  127
  128                /********************************
  129                *          UPDATE INDEX         *
  130                ********************************/
  131
  132:- thread_local
  133    silent/0.
 $update_library_index
Called from make/0 to update the index of the library for each library directory that has a writable index. Note that in the Windows version access_file/2 is mostly bogus. We assert silent/0 to suppress error messages.
  142'$update_library_index' :-
  143    setof(Dir, writable_indexed_directory(Dir), Dirs),
  144    !,
  145    setup_call_cleanup(
  146        asserta(silent, Ref),
  147        guarded_make_library_index(Dirs),
  148        erase(Ref)),
  149    (   flag('$modified_index', true, false)
  150    ->  reload_library_index
  151    ;   true
  152    ).
  153'$update_library_index'.
  154
  155guarded_make_library_index([]).
  156guarded_make_library_index([Dir|Dirs]) :-
  157    (   catch(make_library_index(Dir), E,
  158              print_message(error, E))
  159    ->  true
  160    ;   print_message(warning, goal_failed(make_library_index(Dir)))
  161    ),
  162    guarded_make_library_index(Dirs).
 writable_indexed_directory(-Dir) is nondet
True when Dir is an indexed library directory with a writable index, i.e., an index that can be updated.
  169writable_indexed_directory(Dir) :-
  170    index_file_name(IndexFile, autoload('INDEX'), [access([read,write])]),
  171    file_directory_name(IndexFile, Dir).
  172writable_indexed_directory(Dir) :-
  173    absolute_file_name(library('MKINDEX'),
  174                       [ file_type(prolog),
  175                         access(read),
  176                         solutions(all),
  177                         file_errors(fail)
  178                       ], MkIndexFile),
  179    file_directory_name(MkIndexFile, Dir),
  180    plfile_in_dir(Dir, 'INDEX', _, IndexFile),
  181    access_file(IndexFile, write).
  182
  183
  184                /********************************
  185                *           LOAD INDEX          *
  186                ********************************/
 reload_library_index
Reload the index on the next call
  192reload_library_index :-
  193    context_module(M),
  194    reload_library_index(M).
  195
  196reload_library_index(M) :-
  197    with_mutex('$autoload', clear_library_index(M)).
  198
  199clear_library_index(M) :-
  200    retractall(M:library_index(_, _, _)),
  201    retractall(M:autoload_directories(_)),
  202    retractall(M:index_checked_at(_)).
 load_library_index(?Name, ?Arity) is det
 load_library_index(?Name, ?Arity, :IndexSpec) is det
Try to find Name/Arity in the library. If the predicate is there, we are happy. If not, we check whether the set of loaded libraries has changed and if so we reload the index.
  212:- meta_predicate load_library_index(?, ?, :).  213:- public load_library_index/3.  214
  215load_library_index(Name, Arity) :-
  216    load_library_index(Name, Arity, autoload('INDEX')).
  217
  218load_library_index(Name, Arity, M:_Spec) :-
  219    atom(Name), integer(Arity),
  220    functor(Head, Name, Arity),
  221    M:library_index(Head, _, _),
  222    !.
  223load_library_index(_, _, Spec) :-
  224    notrace(with_mutex('$autoload', load_library_index_p(Spec))).
  225
  226load_library_index_p(M:_) :-
  227    M:index_checked_at(Time),
  228    get_time(Now),
  229    Now-Time < 60,
  230    !.
  231load_library_index_p(M:Spec) :-
  232    findall(Index, index_file_name(Index, Spec, [access(read)]), List0),
  233    '$list_to_set'(List0, List),
  234    retractall(M:index_checked_at(_)),
  235    get_time(Now),
  236    assert(M:index_checked_at(Now)),
  237    (   M:autoload_directories(List)
  238    ->  true
  239    ;   retractall(M:library_index(_, _, _)),
  240        retractall(M:autoload_directories(_)),
  241        read_index(List, M),
  242        assert(M:autoload_directories(List))
  243    ).
 index_file_name(-IndexFile, +Spec, +Options) is nondet
True if IndexFile is an autoload index file. Options is passed to absolute_file_name/3. This predicate searches the path autoload.
See also
- file_search_path/2.
  253index_file_name(IndexFile, FileSpec, Options) :-
  254    absolute_file_name(FileSpec,
  255                       IndexFile,
  256                       [ file_type(prolog),
  257                         solutions(all),
  258                         file_errors(fail)
  259                       | Options
  260                       ]).
  261
  262read_index([], _) :- !.
  263read_index([H|T], M) :-
  264    !,
  265    read_index(H, M),
  266    read_index(T, M).
  267read_index(Index, M) :-
  268    print_message(silent, autoload(read_index(Dir))),
  269    file_directory_name(Index, Dir),
  270    setup_call_cleanup(
  271        '$push_input_context'(autoload_index),
  272        setup_call_cleanup(
  273            open(Index, read, In),
  274            read_index_from_stream(Dir, In, M),
  275            close(In)),
  276        '$pop_input_context').
  277
  278read_index_from_stream(Dir, In, M) :-
  279    repeat,
  280        read(In, Term),
  281        assert_index(Term, Dir, M),
  282    !.
  283
  284assert_index(end_of_file, _, _) :- !.
  285assert_index(index(Name, Arity, Module, File), Dir, M) :-
  286    !,
  287    functor(Head, Name, Arity),
  288    atomic_list_concat([Dir, '/', File], Path),
  289    assertz(M:library_index(Head, Module, Path)),
  290    fail.
  291assert_index(Term, Dir, _) :-
  292    print_message(error, illegal_autoload_index(Dir, Term)),
  293    fail.
  294
  295
  296                /********************************
  297                *       CREATE INDEX.pl         *
  298                ********************************/
 make_library_index(+Dir) is det
Create an index for autoloading from the directory Dir. The index file is called INDEX.pl. In Dir contains a file MKINDEX.pl, this file is loaded and we assume that the index is created by directives that appearin this file. Otherwise, all source files are scanned for their module-header and all exported predicates are added to the autoload index.
See also
- make_library_index/2
  311make_library_index(Dir0) :-
  312    forall(absolute_file_name(Dir0, Dir,
  313                              [ expand(true),
  314                                file_type(directory),
  315                                file_errors(fail),
  316                                solutions(all)
  317                              ]),
  318           make_library_index2(Dir)).
  319
  320make_library_index2(Dir) :-
  321    plfile_in_dir(Dir, 'MKINDEX', _MkIndex, AbsMkIndex),
  322    access_file(AbsMkIndex, read),
  323    !,
  324    load_files(user:AbsMkIndex, [silent(true)]).
  325make_library_index2(Dir) :-
  326    findall(Pattern, source_file_pattern(Pattern), PatternList),
  327    make_library_index2(Dir, PatternList).
 make_library_index(+Dir, +Patterns:list(atom)) is det
Create an autoload index INDEX.pl for Dir by scanning all files that match any of the file-patterns in Patterns. Typically, this appears as a directive in MKINDEX.pl. For example:
:- prolog_load_context(directory, Dir),
   make_library_index(Dir, ['*.pl']).
See also
- make_library_index/1.
  342make_library_index(Dir0, Patterns) :-
  343    forall(absolute_file_name(Dir0, Dir,
  344                              [ expand(true),
  345                                file_type(directory),
  346                                file_errors(fail),
  347                                solutions(all)
  348                              ]),
  349           make_library_index2(Dir, Patterns)).
  350
  351make_library_index2(Dir, Patterns) :-
  352    plfile_in_dir(Dir, 'INDEX', _Index, AbsIndex),
  353    ensure_slash(Dir, DirS),
  354    pattern_files(Patterns, DirS, Files),
  355    (   library_index_out_of_date(Dir, AbsIndex, Files)
  356    ->  do_make_library_index(AbsIndex, DirS, Files),
  357        flag('$modified_index', _, true)
  358    ;   true
  359    ).
  360
  361ensure_slash(Dir, DirS) :-
  362    (   sub_atom(Dir, _, _, 0, /)
  363    ->  DirS = Dir
  364    ;   atom_concat(Dir, /, DirS)
  365    ).
  366
  367source_file_pattern(Pattern) :-
  368    user:prolog_file_type(PlExt, prolog),
  369    PlExt \== qlf,
  370    atom_concat('*.', PlExt, Pattern).
  371
  372plfile_in_dir(Dir, Base, PlBase, File) :-
  373    file_name_extension(Base, pl, PlBase),
  374    atomic_list_concat([Dir, '/', PlBase], File).
  375
  376pattern_files([], _, []).
  377pattern_files([H|T], DirS, Files) :-
  378    atom_concat(DirS, H, P0),
  379    expand_file_name(P0, Files0),
  380    '$append'(Files0, Rest, Files),
  381    pattern_files(T, DirS, Rest).
  382
  383library_index_out_of_date(_Dir, Index, _Files) :-
  384    \+ exists_file(Index),
  385    !.
  386library_index_out_of_date(Dir, Index, Files) :-
  387    time_file(Index, IndexTime),
  388    (   time_file(Dir, DotTime),
  389        DotTime > IndexTime
  390    ;   '$member'(File, Files),
  391        time_file(File, FileTime),
  392        FileTime > IndexTime
  393    ),
  394    !.
  395
  396
  397do_make_library_index(Index, Dir, Files) :-
  398    ensure_slash(Dir, DirS),
  399    '$stage_file'(Index, StagedIndex),
  400    setup_call_catcher_cleanup(
  401        open(StagedIndex, write, Out),
  402        ( print_message(informational, make(library_index(Dir))),
  403          index_header(Out),
  404          index_files(Files, DirS, Out)
  405        ),
  406        Catcher,
  407        install_index(Out, Catcher, StagedIndex, Index)).
  408
  409install_index(Out, Catcher, StagedIndex, Index) :-
  410    catch(close(Out), Error, true),
  411    (   silent
  412    ->  OnError = silent
  413    ;   OnError = error
  414    ),
  415    (   var(Error)
  416    ->  TheCatcher = Catcher
  417    ;   TheCatcher = exception(Error)
  418    ),
  419    '$install_staged_file'(TheCatcher, StagedIndex, Index, OnError).
 index_files(+Files, +Directory, +Out:stream) is det
Write index for Files in Directory to the stream Out.
  425index_files([], _, _).
  426index_files([File|Files], DirS, Fd) :-
  427    catch(setup_call_cleanup(
  428              open(File, read, In),
  429              read(In, Term),
  430              close(In)),
  431          E, print_message(warning, E)),
  432    (   Term = (:- module(Module, Public)),
  433        is_list(Public)
  434    ->  atom_concat(DirS, Local, File),
  435        file_name_extension(Base, _, Local),
  436        forall(public_predicate(Public, Name/Arity),
  437               format(Fd, 'index((~k), ~k, ~k, ~k).~n',
  438                      [Name, Arity, Module, Base]))
  439    ;   true
  440    ),
  441    index_files(Files, DirS, Fd).
  442
  443public_predicate(Public, PI) :-
  444    '$member'(PI0, Public),
  445    canonical_pi(PI0, PI).
  446
  447canonical_pi(Var, _) :-
  448    var(Var), !, fail.
  449canonical_pi(Name/Arity, Name/Arity).
  450canonical_pi(Name//A0,   Name/Arity) :-
  451    Arity is A0 + 2.
  452
  453
  454index_header(Fd):-
  455    format(Fd, '/*  Creator: make/0~n~n', []),
  456    format(Fd, '    Purpose: Provide index for autoload~n', []),
  457    format(Fd, '*/~n~n', []).
  458
  459
  460                 /*******************************
  461                 *            EXTENDING         *
  462                 *******************************/
 autoload_path(+Path) is det
Add Path to the libraries that are used by the autoloader. This extends the search path autoload and reloads the library index. For example:
:- autoload_path(library(http)).

If this call appears as a directive, it is term-expanded into a clause for file_search_path/2 and a directive calling reload_library_index/0. This keeps source information and allows for removing this directive.

  479autoload_path(Alias) :-
  480    (   user:file_search_path(autoload, Alias)
  481    ->  true
  482    ;   assertz(user:file_search_path(autoload, Alias)),
  483        reload_library_index
  484    ).
  485
  486system:term_expansion((:- autoload_path(Alias)),
  487                      [ user:file_search_path(autoload, Alias),
  488                        (:- reload_library_index)
  489                      ]).
  490
  491
  492		 /*******************************
  493		 *      RUNTIME AUTOLOADER	*
  494		 *******************************/
Provide PI by autoloading. This checks:
  504'$autoload'(PI) :-
  505    source_location(File, _Line),
  506    !,
  507    setup_call_cleanup(
  508        '$start_aux'(File, Context),
  509        '$autoload2'(PI),
  510        '$end_aux'(File, Context)).
  511'$autoload'(PI) :-
  512    '$autoload2'(PI).
  513
  514'$autoload2'(PI) :-
  515    setup_call_cleanup(
  516        leave_sandbox(Old),
  517        '$autoload3'(PI),
  518        restore_sandbox(Old)).
  519
  520leave_sandbox(Sandboxed) :-
  521    current_prolog_flag(sandboxed_load, Sandboxed),
  522    set_prolog_flag(sandboxed_load, false).
  523restore_sandbox(Sandboxed) :-
  524    set_prolog_flag(sandboxed_load, Sandboxed).
  525
  526'$autoload3'(PI) :-
  527    autoload_from(PI, LoadModule, FullFile),
  528    do_autoload(FullFile, PI, LoadModule).
 autoload_from(+PI, -LoadModule, -File) is semidet
True when PI can be defined by loading File which is defined the module LoadModule.
  535autoload_from(Module:PI, LoadModule, FullFile) :-
  536    autoload_in(Module, explicit),
  537    current_autoload(Module:File, Ctx, import(Imports)),
  538    memberchk(PI, Imports),
  539    library_info(File, Ctx, FullFile, LoadModule, Exports),
  540    (   pi_in_exports(PI, Exports)
  541    ->  !
  542    ;   autoload_error(Ctx, not_exported(PI, File, FullFile, Exports)),
  543        fail
  544    ).
  545autoload_from(Module:Name/Arity, LoadModule, FullFile) :-
  546    autoload_in(Module, explicit),
  547    PI = Name/Arity,
  548    current_autoload(Module:File, Ctx, all),
  549    library_info(File, Ctx, FullFile, LoadModule, Exports),
  550    pi_in_exports(PI, Exports).
  551autoload_from(Module:Name/Arity, LoadModule, Library) :-
  552    autoload_in(Module, general),
  553    '$find_library'(Module, Name, Arity, LoadModule, Library).
  554
  555:- public autoload_in/2.                        % used in syspred
  556
  557autoload_in(Module, How) :-
  558    current_prolog_flag(autoload, AutoLoad),
  559    autoload_in(AutoLoad, How, Module),
  560    !.
 autoload_in(+AutoloadFlag, +AutoloadMode, +TargetModule) is semidet
  564autoload_in(true,             _,        _).
  565autoload_in(explicit,         explicit, _).
  566autoload_in(explicit_or_user, explicit, _).
  567autoload_in(user,             explicit, user).
  568autoload_in(explicit_or_user, explicit, _).
  569autoload_in(user,             _,        user).
  570autoload_in(explicit_or_user, general,  user).
 do_autoload(+File, :PI, +LoadModule) is det
Load File, importing PI into the qualified module. File is known to define LoadModule. There are three cases:
  586do_autoload(Library, Module:Name/Arity, LoadModule) :-
  587    functor(Head, Name, Arity),
  588    '$update_autoload_level'([autoload(true)], Old),
  589    verbose_autoload(Module:Name/Arity, Library),
  590    '$compilation_mode'(OldComp, database),
  591    (   Module == LoadModule
  592    ->  ensure_loaded(Module:Library)
  593    ;   (   '$c_current_predicate'(_, LoadModule:Head),
  594            '$get_predicate_attribute'(LoadModule:Head, defined, 1),
  595            \+ '$loading'(Library)
  596        ->  Module:import(LoadModule:Name/Arity)
  597        ;   use_module(Module:Library, [Name/Arity])
  598        )
  599    ),
  600    '$set_compilation_mode'(OldComp),
  601    '$set_autoload_level'(Old),
  602    '$c_current_predicate'(_, Module:Head).
  603
  604verbose_autoload(PI, Library) :-
  605    current_prolog_flag(verbose_autoload, true),
  606    !,
  607    set_prolog_flag(verbose_autoload, false),
  608    print_message(informational, autoload(PI, Library)),
  609    set_prolog_flag(verbose_autoload, true).
  610verbose_autoload(PI, Library) :-
  611    print_message(silent, autoload(PI, Library)).
 autoloadable(:Head, -File) is nondet
True when Head can be autoloaded from File. This implements the predicate_property/2 property autoload(File). The module muse be instantiated.
  620:- public                               % used from predicate_property/2
  621    autoloadable/2.  622
  623autoloadable(M:Head, FullFile) :-
  624    atom(M),
  625    current_module(M),
  626    autoload_in(M, explicit),
  627    (   callable(Head)
  628    ->  goal_name_arity(Head, Name, Arity),
  629        autoload_from(M:Name/Arity, _, FullFile)
  630    ;   findall((M:H)-F, autoloadable_2(M:H, F), Pairs),
  631        (   '$member'(M:Head-FullFile, Pairs)
  632        ;   current_autoload(M:File, Ctx, all),
  633            library_info(File, Ctx, FullFile, _, Exports),
  634            '$member'(PI, Exports),
  635            '$pi_head'(PI, Head),
  636            \+ memberchk(M:Head-_, Pairs)
  637        )
  638    ).
  639autoloadable(M:Head, FullFile) :-
  640    (   var(M)
  641    ->  autoload_in(any, general)
  642    ;   autoload_in(M, general)
  643    ),
  644    (   callable(Head)
  645    ->  goal_name_arity(Head, Name, Arity),
  646        (   '$find_library'(_, Name, Arity, _, FullFile)
  647        ->  true
  648        )
  649    ;   '$in_library'(Name, Arity, autoload),
  650        functor(Head, Name, Arity)
  651    ).
  652
  653
  654autoloadable_2(M:Head, FullFile) :-
  655    current_autoload(M:File, Ctx, import(Imports)),
  656    library_info(File, Ctx, FullFile, _LoadModule, _Exports),
  657    '$member'(PI, Imports),
  658    '$pi_head'(PI, Head).
  659
  660goal_name_arity(Head, Name, Arity) :-
  661    compound(Head),
  662    !,
  663    compound_name_arity(Head, Name, Arity).
  664goal_name_arity(Head, Head, 0).
 library_info(+Spec, +AutoloadContext, -FullFile, -Module, -Exports)
Find information about a library.
  670library_info(Spec, _, FullFile, Module, Exports) :-
  671    '$resolved_source_path'(Spec, FullFile, []),
  672    !,
  673    (   \+ '$loading_file'(FullFile, _Queue, _LoadThread)
  674    ->  '$current_module'(Module, FullFile),
  675        '$module_property'(Module, exports(Exports))
  676    ;   library_info_from_file(FullFile, Module, Exports)
  677    ).
  678library_info(Spec, Context, FullFile, Module, Exports) :-
  679    (   Context = (Path:_Line)
  680    ->  Extra = [relative_to(Path)]
  681    ;   Extra = []
  682    ),
  683    (   absolute_file_name(Spec, FullFile,
  684                           [ file_type(prolog),
  685                             access(read),
  686                             file_errors(fail)
  687                           | Extra
  688                           ])
  689    ->  '$register_resolved_source_path'(Spec, FullFile),
  690        library_info_from_file(FullFile, Module, Exports)
  691    ;   autoload_error(Context, no_file(Spec)),
  692        fail
  693    ).
  694
  695
  696library_info_from_file(FullFile, Module, Exports) :-
  697    setup_call_cleanup(
  698        '$open_source'(FullFile, In, State, [], []),
  699        '$term_in_file'(In, _Read, _RLayout, Term, _TLayout, _Stream,
  700                        [FullFile], []),
  701        '$close_source'(State, true)),
  702    (   Term = (:- module(Module, Exports))
  703    ->  !
  704    ;   nonvar(Term),
  705        skip_header(Term)
  706    ->  fail
  707    ;   '$domain_error'(module_header, Term)
  708    ).
  709
  710skip_header(begin_of_file).
  711
  712
  713:- dynamic printed/3.  714:- volatile printed/3.  715
  716autoload_error(Context, Error) :-
  717    suppress(Context, Error),
  718    !.
  719autoload_error(Context, Error) :-
  720    get_time(Now),
  721    assertz(printed(Context, Error, Now)),
  722    print_message(warning, error(autoload(Error), autoload(Context))).
  723
  724suppress(Context, Error) :-
  725    printed(Context, Error, Printed),
  726    get_time(Now),
  727    (   Now - Printed < 1
  728    ->  true
  729    ;   retractall(printed(Context, Error, _)),
  730        fail
  731    ).
  732
  733
  734		 /*******************************
  735		 *            CALLBACK		*
  736		 *******************************/
  737
  738:- public
  739    set_autoload/1.
 set_autoload(+Value) is det
Hook called from set_prolog_flag/2 when autoloading is switched. If the desired value is false we should materialize all registered requests for autoloading. We must do so before disabling autoloading as loading the files may require autoloading.
  748set_autoload(FlagValue) :-
  749    current_prolog_flag(autoload, FlagValue),
  750    !.
  751set_autoload(FlagValue) :-
  752    \+ autoload_in(FlagValue, explicit, any),
  753    !,
  754    setup_call_cleanup(
  755        nb_setval('$autoload_disabling', true),
  756        materialize_autoload(Count),
  757        nb_delete('$autoload_disabling')),
  758    print_message(informational, autoload(disabled(Count))).
  759set_autoload(_).
  760
  761materialize_autoload(Count) :-
  762    State = state(0),
  763    forall(current_predicate(M:'$autoload'/3),
  764           materialize_autoload(M, State)),
  765    arg(1, State, Count).
  766
  767materialize_autoload(M, State) :-
  768    (   current_autoload(M:File, Context, Import),
  769        library_info(File, Context, FullFile, _LoadModule, _Exports),
  770        arg(1, State, N0),
  771        N is N0+1,
  772        nb_setarg(1, State, N),
  773        (   Import == all
  774        ->  verbose_autoload(M:all, FullFile),
  775            use_module(M:FullFile)
  776        ;   Import = import(Preds)
  777        ->  verbose_autoload(M:Preds, FullFile),
  778            use_module(M:FullFile, Preds)
  779        ),
  780        fail
  781    ;   true
  782    ),
  783    abolish(M:'$autoload'/3).
  784
  785
  786		 /*******************************
  787		 *          AUTOLOAD/2		*
  788		 *******************************/
  789
  790autoload(M:File) :-
  791    (   \+ autoload_in(M, explicit)
  792    ;   nb_current('$autoload_disabling', true)
  793    ),
  794    !,
  795    use_module(M:File).
  796autoload(M:File) :-
  797    '$must_be'(filespec, File),
  798    source_context(Context),
  799    (   current_autoload(M:File, _, import(all))
  800    ->  true
  801    ;   assert_autoload(M:'$autoload'(File, Context, all))
  802    ).
  803
  804autoload(M:File, Imports) :-
  805    (   \+ autoload_in(M, explicit)
  806    ;   nb_current('$autoload_disabling', true)
  807    ),
  808    !,
  809    use_module(M:File, Imports).
  810autoload(M:File, Imports0) :-
  811    '$must_be'(filespec, File),
  812    valid_imports(Imports0, Imports),
  813    source_context(Context),
  814    register_autoloads(Imports, M, File, Context),
  815    (   current_autoload(M:File, _, import(Imports))
  816    ->  true
  817    ;   assert_autoload(M:'$autoload'(File, Context, import(Imports)))
  818    ).
  819
  820source_context(Path:Line) :-
  821    source_location(Path, Line),
  822    !.
  823source_context(-).
  824
  825assert_autoload(Clause) :-
  826    '$initialization_context'(Source, Ctx),
  827    '$store_admin_clause2'(Clause, _Layout, Source, Ctx).
  828
  829valid_imports(Imports0, Imports) :-
  830    '$must_be'(list, Imports0),
  831    valid_import_list(Imports0, Imports).
  832
  833valid_import_list([], []).
  834valid_import_list([H0|T0], [H|T]) :-
  835    '$pi_head'(H0, Head),
  836    '$pi_head'(H, Head),
  837    valid_import_list(T0, T).
 register_autoloads(+ListOfPI, +Module, +File, +Context)
Put an autoload flag on all predicates declared using autoload/2 to prevent duplicates or the user defining the same predicate.
  844register_autoloads([], _, _, _).
  845register_autoloads([PI|T], Module, File, Context) :-
  846    PI = Name/Arity,
  847    functor(Head, Name, Arity),
  848    (   '$get_predicate_attribute'(Module:Head, autoload, 1)
  849    ->  (   current_autoload(Module:_File0, _Ctx0, import(Imports)),
  850            memberchk(PI, Imports)
  851        ->  '$permission_error'(redefine, imported_procedure, PI),
  852            fail
  853        ;   Done = true
  854        )
  855    ;   '$c_current_predicate'(_, Module:Head), % no auto-import
  856        '$get_predicate_attribute'(Module:Head, imported, From)
  857    ->  (   (   '$resolved_source_path'(File, FullFile)
  858            ->  true
  859            ;   '$resolve_source_path'(File, FullFile, [])
  860            ),
  861            module_property(From, file(FullFile))
  862        ->  Done = true
  863        ;   print_message(warning,
  864                          autoload(already_defined(Module:PI, From))),
  865            Done = true
  866        )
  867    ;   true
  868    ),
  869    (   Done == true
  870    ->  true
  871    ;   '$set_predicate_attribute'(Module:Head, autoload, 1)
  872    ),
  873    register_autoloads(T, Module, File, Context).
  874
  875pi_in_exports(PI, Exports) :-
  876    '$member'(E, Exports),
  877    canonical_pi(E, PI),
  878    !.
  879
  880current_autoload(M:File, Context, Term) :-
  881    '$get_predicate_attribute'(M:'$autoload'(_,_,_), defined, 1),
  882    M:'$autoload'(File, Context, Term).
  883
  884                 /*******************************
  885                 *             REQUIRE          *
  886                 *******************************/
 require(:ListOfPredIndicators) is det
Register the predicates in ListOfPredIndicators for autoloading using autoload/2 if they are not system predicates.
  893require(M:Spec) :-
  894    (   is_list(Spec)
  895    ->  List = Spec
  896    ;   phrase(comma_list(Spec), List)
  897    ), !,
  898    require(List, M, FromLib),
  899    keysort(FromLib, Sorted),
  900    by_file(Sorted, Autoload),
  901    forall('$member'(File-Import, Autoload),
  902           autoload(M:File, Import)).
  903require(_:Spec) :-
  904    '$type_error'(list, Spec).
  905
  906require([],_, []).
  907require([H|T], M, Needed) :-
  908   '$pi_head'(H, Head),
  909   (   '$get_predicate_attribute'(system:Head, defined, 1)
  910   ->  require(T, M, Needed)
  911   ;   '$pi_head'(Module:Name/Arity, M:Head),
  912       (   '$find_library'(Module, Name, Arity, LoadModule, Library)
  913       ->  (   current_predicate(LoadModule:Name/Arity)
  914           ->  Module:import(LoadModule:Name/Arity),
  915               require(T, M, Needed)
  916           ;   Needed = [Library-H|More],
  917               require(T, M, More)
  918           )
  919       ;   print_message(error, error(existence_error(procedure, Name/Arity), _)),
  920           require(T, M, Needed)
  921       )
  922   ).
  923
  924by_file([], []).
  925by_file([File-PI|T0], [Spec-[PI|PIs]|T]) :-
  926    on_path(File, Spec),
  927    same_file(T0, File, PIs, T1),
  928    by_file(T1, T).
  929
  930on_path(Library, library(Base)) :-
  931    file_base_name(Library, Base),
  932    findall(Path, plain_source(library(Base), Path), [Library]),
  933    !.
  934on_path(Library, Library).
  935
  936plain_source(Spec, Path) :-
  937    absolute_file_name(Spec, PathExt,
  938                       [ file_type(prolog),
  939                         access(read),
  940                         file_errors(fail),
  941                         solutions(all)
  942                       ]),
  943    file_name_extension(Path, _, PathExt).
  944
  945same_file([File-PI|T0], File, [PI|PIs], T) :-
  946    !,
  947    same_file(T0, File, PIs, T).
  948same_file(List, _, [], List).
  949
  950comma_list(Var) -->
  951    { var(Var),
  952      !,
  953      '$instantiation_error'(Var)
  954    }.
  955comma_list((A,B)) -->
  956    !,
  957    comma_list(A),
  958    comma_list(B).
  959comma_list(A) -->
  960    [A]