Prolog SWI : Logtalk, How do I load my own project files?

问题

so this week consisted of me installing Logtalk, one of the extensions for Prolog. In this case I'm using Prolog SWI, and I've run into a little snag. I'm not sure how to actually consult my own projects using Logtalk. I have taken a look at the examples that Logtalk comes with in order to understand the code itself, and in doing so I've been able to load them and execute them perfectly. What I don't understand though is what is actually going on when logtalk is loading a file, and how I can load my own projects.

I'll take the "hello_world" example as the point of discussion. The file called hello_world, is located in the examples folder of the Logtalk files. and yet it is consulted like so:

| ?- logtalk_load(hello_world(loader)).

First thing I thought was "that is a functor", looking at what it was doing using trace, I found that it was being called from the library and was being told how to get to the examples folder, where it then opened the "hello_world" folder and then the "loader" file. After which normal compiling happened.

I took a look at the library and couldn't figure out what was going on. I also thought that this can't possibly be the practical route to load user created projects in Logtalk. There was another post that was asking how to do this with SWI as well, but it didn't have any replies and didn't look like any effort had been made to figure the problem out.

Now let me be clear on something, I can use the "consult('...')." command just fine, I can even use "consult" to open my projects, however if I do this the logtalk console doesn't seem to be using any of the logtalk extensions and so is just vanilla prolog. I've used an installer for windows to install logtalk and I know that it is working as I've been looking at the examples that it comes with.

I've tried to find a tutorial but it is very difficult to find much of anything for Logtalk, the most I have found is this documentation on loading from within your project:

logtalk_load/1.
logtalk_load/2.

which I understand like so:

logtalk_load(file). % Top level loading
logtalk_load(folder(file). % Bottom level loading

So to save a huge manual load each time I would have a loader file that will load the other components of my project (which is what the examples for Logtalk do). This bit makes sense to me, I think, how I get to my loader file, doesn't.

Whether or not I have been understanding it correctly or not remains to be seen, but even if I have been understanding it correctly, I'm still lost as to how I load my own projects. Thanks for any help you can give, if you could give an example that'll be best as I do learn from examples quite quickly.

LITTLE UPDATE

You asked if I was using a logtalk console for my program running, and I am, I'm using the one that is provided and referred to during the "QUICK_START" file [Start > Programs > Logtalk > "Logtalk - Prolog-SWI (console)"] I thought to double check if the logtalk add ons were working and tested the "birds" example since it uses objects and is a nice familiar example. Yet again, everything works fine when using the logtalk_load/2 functor.

I took a look at what the library path was referring to a bit more given the feedback given so far. Looking into how logtalk loads files. Set up as it is so far, without changing things logtalk consults a folder which contains a prolog file called libpaths. It is basically how the examples are found, all it is is a part way description for where to get a file from. So when I say "logtalk_load/2" from what I can tell at least I'm going to this file and finding where the folder is that I'm asking for.

Now since I have already placed my own project folder in the examples folder, I promptly added my own folder to the list to test if this would at least be a part way solution to help me understand things a bit more. I added the following to the libpaths.pl file.

logtalk_library_path(my_project, examples('my_project/')).
% The path must end in a / so I have done so

So, I've got my folder path declared, got my folder, and the loader file is what I'll be calling when I use the loader. Without thinking about setting my own lib path folder, I should have enough to get things working and do some practical learning. But alas no, seems my investigation failed and I was returned the following:

ERROR: Unhandled exception: existence_error(library,project_aim)

Not what I wanted to see, I'm back to this library error business. I'm missing a reference to my project folder somewhere but I don't know where else it could need referencing. Running trace on the matter didn't help I simply had the following occur:

Call: (17) logtalk_library_path(my_project, _G943) ? creep
Fail: (17) logtalk_library_path(my_project, _G943) ? creep
ERROR: Unhandled exception: existence_error(library,my_project)

The call is failing, I'm simply not finding a reference where ever it is logtalk is looking. And I'm a novice at best when it comes to these sorts of issues, I've been using computers now for only 3 years and programming for the past 2 in visual studios using c# and c++. At least I've shone some more light on the matter, any more helpful advice given this information?

回答1:

Please use the official Logtalk support channels for help in the future. You will get timely replies there. Daniel, thanks for providing help to this user.

I assume that you're using Logtalk 2.x. Note that Logtalk 3.x supports relative and full source file paths. In Logtalk 2.x, the logtalk_compile/1-2 (compile to disk) and logtalk_load/1-2 (compile and load into memory) predicates take either the name of a source file (without the .lgt extension) OR the location of the source file to be loaded using "library notation". To use the former you need first to change the current working directory to the directory containing the file. This makes the second option more flexible. As you mention, the hello_world example you cite, can be loaded by typing:

?- logtalk_load(hello_world(loader)).

or:

?- {hello_world(loader)}.

Logtalk 2.x and 3.x also provide integration with some SWI-Prolog features such as consult/1, make/0, edit/0-1, the graphical tracer and the graphical profiler. For example:

?- [hello_world(loader)].

********** Hello World! **********
% [ /Users/pmoura/logtalk/examples/hello_world/hello_world.lgt loaded ]
% [ /Users/pmoura/logtalk/examples/hello_world/loader.lgt loaded ]
% (0 warnings)
true.

To load your own examples and projects, the easiest way is to add a library path to the directory holding your files to the $LOGTALKUSER/settings.lgt file (%LOGTALKUSER%\settings.lgt on Windows) as Daniel explained. The location of the Logtalk user directory is defined by you when using the provided installer. The default is My Documents\Logtalk in Windows. Editing the libpaths.pl file is not a good idea. Use the settings.lgt file preferentially to define your own library paths. Assuming, as it seems to be your case, that you have created a %LOGTALKUSER%\examples\project_aim directory, add the following lines to your %LOGTALKUSER%\settings.lgt file:

:- multifile(logtalk_library_path/2).
:- dynamic(logtalk_library_path/2).

logtalk_library_path(project_aim, examples('project_aim/').

If you have a %LOGTALKUSER%\examples\project_aim\loader.lgt file, you can then load it by typing:

?- {project_aim(loader)}.

Hope this helps.

回答2:

What makes me uncertain of my answer is just that you claim the usual consult works but not logtalk_load. You do have to run a different program to get to Logtalk than Prolog. In Unix it would be something like swilgt for SWI-Prolog or gplgt for GNU Prolog. I don't have Windows so I can't really tell you what you need to do there, other than maybe make sure you're running a binary named Logtalk and not simply Prolog.

Otherwise I think your basic problem is that in Windows it's hard to control your working directory. In a Unix environment, you'd navigate your terminal over to the directory with your files in it and launch Logtalk or Prolog from there. Then when you name your files they would be in the current directory, so Prolog would have no trouble finding them. If you're running a command-line Prolog, you can probably configure the menu item so that it will do this for you, but you have to know where you want to send it.

You can use the functor notation either to get at subdirectories (so, e.g., foo(bar(baz(bat(afile)))) finds foo\bar\baz\bat\afile.lgt). This you seemed to have figured out, and I can at least corroborate it. This will search in its predefined list of functors, and also in the current directory. But you could launch Logtalk from anywhere and then run, say, assertz(logtalk_library_path(foo, 'C:\foo\bar\baz\bat')). after which logtalk_load(foo(afile)) is going to be expanded to C:\foo\bar\baz\bat\afile.lgt.

Building on that technique, you could put your files in the Logtalk user directory and use $LOGTALKUSER as demonstrated in the documentation. I can't find a definitive reference on where the Logtalk user directory will be on Windows, but I would expect it to be in the Documents and Settings folder for your user. So you could put stuff in there and reference it by defining a new logtalk_library_path like this.

It's nice, but it still leaves you high and dry if you have to keep on re-entering these assertions every time you launch. Fortunately, there is a Logtalk settings file named settings.lgt in your Logtalk user directory which has a chunk of commented-out code near the top:

%  To define a "library" path for your projects, edit and uncomment the
%  following lines (the library path must end with a slash character):

/*
:- multifile(logtalk_library_path/2).
:- dynamic(logtalk_library_path/2).

logtalk_library_path(my_project, '$HOME/my_project/').
logtalk_library_path(my_project_examples, my_project('examples/')).
*/

You can simply uncomment those lines and insert your own stuff to get a persistent shortcut.

You can also write a plrc file for SWI Prolog to define other things to happen at startup. The other option seems cleaner since it's Logtalk-specific, but a plrc is more general.

Once you have that machinery in place, having a loader file will be a lot more helpful.

NOTE: I don't have Windows to test any of this stuff on, so you may need to make either or both of the following changes to the preceeding:

• You may need to use / instead of \ in your paths (or maybe either will work, who knows?). I'd probably try / first because that's how all other systems work.
• You may need to use %LOGTALKUSER% instead of $LOGTALKUSER, depending on how Logtalk expands variables.

Hope this helps and I hope you stick with Logtalk, it could use some passionate users like yourself!

来源：https://stackoverflow.com/questions/15706681/prolog-swi-logtalk-how-do-i-load-my-own-project-files