1/* 
    2	Copyright 2015 Samer Abdallah (UCL)
    3	 
    4	This program is free software; you can redistribute it and/or
    5	modify it under the terms of the GNU Lesser General Public License
    6	as published by the Free Software Foundation; either version 2
    7	of the License, or (at your option) any later version.
    8
    9	This program is distributed in the hope that it will be useful,
   10	but WITHOUT ANY WARRANTY; without even the implied warranty of
   11	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   12	GNU Lesser General Public License for more details.
   13
   14	You should have received a copy of the GNU Lesser General Public
   15	License along with this library; if not, write to the Free Software
   16	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
   17*/
   18
   19:- module(rcutils, 
   20      [  persistent_history/2
   21      ,  confirm_on_halt/0
   22      ]).

   43user:file_search_path(home,Home) :- expand_file_name('~',[Home]).
   44
   45:- use_module(library(hostname)).

 confirm_on_halt is det

Installs confirm_halt/0 as a hook to be called before exitting Prolog.

   49confirm_on_halt :- at_halt(confirm_halt).

 confirm_halt is det

Asks the user to confirm that they want to exit Prolog. If they do not, then cancel_halt/1 is called.

   55confirm_halt :-
   56	write('Are you sure you want to exit? [y/n] '), flush_output,
   57	repeat,
   58	get_single_char(C),
   59	(	C=0'y -> writeln(y)
   60	;	C=0'n -> cancel_halt('Exit cancelled')
   61	;	fail
   62	).
   63
   64:- dynamic persistent_history_stream_file/2.

 persistent_history(+File:text, +Opts:options) is det

This disables SWIs built-in persistent command line history mechanism if it is enabled and replaces it with one that saves the history in an arbitrary file. This can be useful if the history file is in a directory that is kept synchronised among many computers, stored, or backed up in some other way. This history includes comment lines that give show the command line arguments given to swipl each time it is started.

If called during SWI Prolog initialisation (ie in the ~/.swiplrc file, in a command line -g goal, or in a program loaded with -s on the command line) then the line editor and history mechanisms will not have been initialised yet, so you must load whichever line editor library you like (readline or editline) first.

Valid options are:

interval(+Interval:number)

If supplied, the history is saved every Interval seconds. Otherwise, the history is only saved when Prolog exits (using at_halt/1).

For example, the author finds it useful to add the following to his ~/.swiplrc:

:- use_module(library(hostname)).
persistent_history :-
   hostname(Hostname),
   atom_concat('.swipl_history.',Hostname,HistFile),
   load_files(library(readline), [if(not_loaded)]),
   set_prolog_flag(readline, readline), % work around bug in readline foreign library
   persistent_history(HistFile,[interval(60)]).

This means that any program can call persistent_history/0 to get a host specific history file, which is useful when a directory is shared or synchronised across several machines.

   98persistent_history(H,Opts) :- 
   99   current_input(S),
  100	(	persistent_history_stream_file(S,H) -> true
  101	;	persistent_history_stream_file(S,H1) -> throw(persistent_history_mismatch(H1,H))
  102	;	print_message(information, rcutils:history_using_file(H)),
  103		(  \+current_predicate(prolog_history:prolog_history/1)
  104      -> create_prolog_flag(save_history, false, [type(boolean)])
  105      ;  current_prolog_flag(save_history,true) ,
  106         prolog_history:history_loaded(PHFile)
  107      -> prolog_history:write_history(PHFile),
  108         prolog_history(disable),
  109         print_message(information, rcutils:closed_prolog_history(PHFile))
  110      ;  set_prolog_flag(save_history,false)
  111      ),
  112		(exists_file(H) -> histop(S, load(H)); true),
  113		assert(persistent_history_stream_file(S,H)),
  114		current_prolog_flag(os_argv,ARGV),
  115		atomics_to_string(ARGV," ",Command),
  116		history_event('Start: ~s',[Command]),
  117		at_halt(history_event('Halt',[])),
  118      (  option(interval(Interval),Opts)
  119      -> print_message(information, rcutils:history_save_interval(Interval)), 
  120         periodic_save_history(Interval)
  121      ;  histop(S, save(H))
  122      )
  123	).
  124
  125history_event(Msg,Args) :-
  126	persistent_history_stream_file(S,H),
  127	get_time(Now),
  128	format_time(string(Time),'%+',Now),
  129	format(string(Info),Msg,Args),
  130	format(atom(Line),'% ~w | ~s',[Time,Info]),
  131	debug(history,'History event: ~s',[Line]),
  132   histop(S, add(Line)),
  133	histop(S, save(H)).
  134
  135
  136periodic_save_history(Interval) :-
  137	persistent_history_stream_file(S,H),
  138	debug(history,'Saving history to "~s"...',[H]),
  139   histop(S, save(H)),
  140   alarm(Interval,periodic_save_history(Interval),_,[remove(true)]).
  141
  142histop(S,Op) :- once(prolog:history(S,Op)).
  143
  144prolog:message(rcutils:history_using_file(H))    --> ['Using persistent history file: "~s"'-[H]].
  145prolog:message(rcutils:history_save_interval(I)) --> ['Will save history every ~w seconds.'-[I]].
  146prolog:message(rcutils:closed_prolog_history(F)) --> ['Saved final prolog_history snapshot to ~w.'-[F]]