In Yap, I'm debugging a program and it reads a lot data from a file. I would like to ask whether there are some ways to set a break-point to a LINE in prolog file. I know there is a predicate called spy which allows you to set the program stop at an expected predicate, however if this predicate calls sub-predicates, how can I set a break-point to the sub-predicates? For example:
pA :-
pB,
pC.
How can I set a break-point to stop at pC(in case pC is a built-in predicate) since spy only allows me to set break-point at pA. Thanks very much for your answer.
The current Logtalk git version supports the definition of file line number spy points. YAP is one Prolog backend compilers supported by Logtalk. The feasibility of using the Logtalk debugger for debugging your program depends, however, if it's structured using Prolog modules. If so, it should be possible to compile your Prolog modules as objects by simply changing the file name extensions from Prolog to Logtalk (i.e. from .pl or .yap to .lgt) and using the Logtalk compiling and loading predicates.
Related
Being new to prolog I am reading existing code (as well as trying to write some code). Having some prior background in semweb I started to play with it and see something that is confusing me. Example assertion:
?- rdf_assert(ex:bob, rdf:type, foaf:'Person').
I also did find the following in the documentation:
Remember: Internally, all resources are atoms. The transformations
above are realised at compile-time using rules for goal_expansion/2
provided by the rdf_db library
Am I correct in assuming that somehow the library is treating the three URIs as atoms? I thought that the compiler would treat this as module_name:predicate, but that does not seem to be the case. If that is true, could you please provide a simple example on how this could be done in prolog?
Thanks
Prolog is not a functional language. This implies 2+3 does not evaluate to 5 and is just a term that gets meaning from the predicate that processes it. Likewise, ex:bob is just a term that has no direct relations to modules or
predicates. Only predicates such call/1 will interpret this as "call bob in the module ex".
Next to that, (SWI-)Prolog (most Prolog's, but not all) have term expansion that allows you to rewrite the term that is read before it is handed to the compiler. That is used to rewrite the argument of rdf/3: each appearance of prefix:local is expanded to a full atom. You can check that by using listing/1 on predicates that call rdf/3 using the prefix notation.
See also rdf_meta
Is there a workaround to make ensure_loaded/1 work
in GNU Prolog as it works in many other Prolog systems?
The goal is to have a preamble so that the rest of
code can use ensure_loaded/1 independent of whether which
Prolog system I use.
I tried the following:
:- multifile(term_expansion/2).
term_expansion((:- ensure_loaded(X)),
(:- atom_concat('<base>\\', X, Y),
include(Y))).
But the following query doesn't work:
:- ensure_loaded('suite.p').
The path calculation itself is not the issue of the question,
but the redefinition of a directive in GNU Prolog. There is
another directive that causes problems: meta_predicate/1. The
byte code crashes as follows:
Bye
A partial solution is:
ensure_loaded(File) :-
absolute_file_name(File, Path),
( predicate_property(_, prolog_file(Path)) ->
true
; consult(Path)
).
It assumes that the file defines at least one predicate but that's a sensible assumption. However, there's seems to be no way to override the native, non-functional, definition of the ensure_loaded/1 directive. A workaround would be to wrap the ensure_loaded/1 directive within an initialization/1 directive. For example:
:- initialization(ensure_loaded('suite.pl')).
Hence this being a partial solution as we're really defining an ensure_loaded/1 predicate, not a directive.
My current speculation is, that it is impossible with
the standard distribution of GNU Prolog 1.4.4. The
docu says:
The GNU Prolog compiler (section 4.4) automatically calls
expand_term/2 on each Term1 read in. However, in the current release,
only DCG transformation are done by the compiler (i.e.
term_expansion/2 cannot be used). To use term_expansion/2, it is
necessary to call expand_term/2 explicitly.
I also tried to inject some Prolog code for term_expansion/2
via the command line, but to no awail. Although the tool chain
has options such as -O, -L, -A that pass options to other tools.
There is not really an option that passes a Prolog text to the
pl2wam, in course of the execution of a consult/1 issued inside
the top-level.
At least this are my results so far.
Bye
m4 can be used with different programming languages because its default policy on unrecognised text is to output and it has a quoting mechanism required for convenient preprocessor usage. I mean, I can write preprocessed code in such a way that my IDE thinks it's Ada. m4 macro invocations (include, define) are hidden in Ada comments. Ada comments start with --, Prolog comments start with % or inside /* */. I can't mix Ada and Prolog easily.
m4 does preprocessing well enough, but its programming side sucks. I thought: why don't me try a general purpose language instead? Prolog looks like being appropriate for my tasks. Prolog has ISO standard, and logic programming looks being useful for reasoning about source generation.
So here we are: we have an arbitrary output language (Ada, then JavaScript, then maybe something else), and it would be nice to write source code in native IDEs for corresponding languages most of the time. I need preprocessor to have a proper parser (like m4 has). This parser shouldn't have Ada syntax knowledge, instead it should only know Ada lexical, and it should be possible to make its macro invocations look like Ada functions invocations.
Its command line interface should look similar to m4 or gcc -E. It should be possible to do both kinds of includes: pure Prolog source code and preprocessed code.
If you know how can I shortly achieve these goals, please write here. I can probably accept non-Prolog solutions, but among the others I prefer standard languages. m4 is part of POSIX, for example.
Prolog is an unusual choice for this task. Indeed, SWI-Prolog used to have the possibility to invoke C preprocessor - should has been removed now, because of its little usefulness.
Anyway, a DCG could be used. I would advice against it if you are not really proficient in Prolog, because debugging can be difficult:
prep(I, O) :-
phrase(exp, I, O).
exp --> mac, !, exp.
exp, [C] --> [C], exp.
exp --> [].
% macro definitions, use 'pushback' argument to change text
mac, "AAA" --> "a".
mac, "G" --> "goal".
example
?- prep("my goal is mars", X).
X = "my G is mAAArs" .
edit: from SWI-Prolog mailing list, WRT the latest release 6.3.18
MODIFIED: Deleted preprocessor/2 after discussion on the
mailinglist. Code relying on this (we hope none) can use the hook
user:prolog_load_file/2 to achieve the same result.
I think the functionality available is more or less that of #include <...>.
For macro expansion (or better, term rewrite) in Prolog there is goal_expansion or term_expansion
edit: latest release brings quasiquotations. Together with a parser in DCG could help to achieve the transformation.
Have you looked at StringTemplate? It's a part of ANTLR (compiler construction toolket). It's written in Java (though there's a C# port, among others). An ANTLR grammar can be written to target many different languages. StringTemplate is what it uses to generate code for the different target languages.
Check it out.
http://antlr.org
http://stringtemplate.org
http://www.cs.usfca.edu/~parrt/
I use DCGs to generate python scripts for FontForge (to create and maintain candlestick fonts for forex trading); I tried M4 scripts but they are not easily amenable to programming (as you mention) and difficult to merge with my glyph definitions that reside in a Prolog database.
DCGs are perceived to be mainly for parsing; but I find they are like a templating engine on their own.
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?
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.
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!
In many Prolog systems it is easy to add a new search path for consulting file.
In Yap for example, the predicate I know it is add_to_path(NewPath).
Is there a way to do the same in SWI Prolog ?. My question is specifically about adding one path to the already existing paths, I am aware of the file_search_path/2 predicate for declaring directories, and the cd/1 predicate for changing the current directory, but I would like to know if there is an alternative method, like the one I found in Yap.
thanks in advance !
There are several mechanisms to this. The first one I met was in C-Prolog, which indeed used clauses for library_directory/1. The current SWI-Prolog mechanism is derived from Quintus and also used in SICStus. It generalises from the library_directory/1 approach
be treating expressions of the form <alias>(Path) as a search over the path-alias <alias>.
Paths for an alias are defined using the predicate file_search_path/2. Now, library is just an alias. Normally, libraries are added using a clause file_search_path(library, Dir).
This mechanism has proven to be pretty flexible. Of course, it would be nice if Prolog systems get more compatible here. I think todays YAP also supports the file_search_path system. (2016 Edit: It does indeed, see YAP Prolog User's Manual: Changing the Compiler’s Behavior)
In your .plrc/.yaprc/.sicstusrc/.swiplrc:
:- multifile(library_directory/1).
library_directory('/home/ulrich/lftp/Prolog-inedit').