{"id":2433,"date":"2021-06-06T13:58:42","date_gmt":"2021-06-06T08:28:42","guid":{"rendered":"https:\/\/www.rangakrish.com\/?p=2433"},"modified":"2021-06-06T14:01:30","modified_gmt":"2021-06-06T08:31:30","slug":"getting-to-know-visual-prolog-10","status":"publish","type":"post","link":"https:\/\/www.rangakrish.com\/index.php\/2021\/06\/06\/getting-to-know-visual-prolog-10\/","title":{"rendered":"Getting to Know Visual Prolog 10"},"content":{"rendered":"

Visual Prolog<\/strong><\/em><\/a>\u00a0has its roots in Turbo Prolog<\/strong><\/em>, which was popularized by Borland<\/strong><\/em> in the mid 1980s. It is developed and supported by PDC A\/S<\/strong><\/em>, Denmark<\/strong><\/em><\/a>.<\/p>\n

So how is Visual Prolog<\/strong><\/em> different from other Prolog<\/strong><\/em> implementations out there, for example, SWI-Prolog<\/strong><\/em><\/a> or Sicstus Prolog<\/strong><\/em><\/a>?<\/p>\n

Here are the key differences:<\/p>\n

1) It is not an ISO<\/em><\/strong> Prolog\u00a0<\/span><\/p>\n

2) It is strongly-typed and is object-oriented<\/p>\n

3) It is a compiled environment, not interpreted<\/p>\n

Visual Prolog<\/strong><\/em> is quite rich in functionality. We can quickly build Console<\/strong><\/em> mode or GUI<\/strong><\/em>-based applications, DLLs<\/strong><\/em>, and even Windows Service<\/strong><\/em> using the platform. Because of strong typing and compile-only strategy, the efficiency of generated code is likely to be superior compared to other interpreted environments. So, if you don’t need a “Standard”<\/strong> Prolog<\/strong><\/em>, then Visual Prolog<\/strong><\/em> has a lot to offer.<\/p>\n

Although I purchased the Commercial Edition of Visual Prolog<\/strong><\/em> a few years ago, I never got around to using it. One reason is that it seems to have a steeper learning curve and there are not many video tutorials to explain the language and the environment. There are a couple of PDF books but they cover an older version (ver 7.x or earlier).<\/p>\n

I upgraded to the latest version (ver 10) a couple of weeks ago and decided to spend some time understanding the language and the environment.<\/p>\n

Instead of writing the canonical\u00a0“Hello, world!<\/strong>“<\/strong><\/em> program, I wanted to start by implementing a DLL<\/strong><\/em> that I can call from C\/C++<\/strong><\/em>. I do this usually with other languages too, see for example this<\/strong><\/em><\/a> and this<\/strong><\/em><\/a>. The capability to use DLLs<\/strong><\/em> (in Windows environment) written in one language can come in handy if we want to exploit the language’s special features for implementing specific functionalities, even though the main application is written in another language say, Erlang<\/strong><\/em>, Go<\/strong><\/em>, etc. In that sense, since Prolog<\/strong><\/em> is a declarative<\/strong><\/em> language and is good at logical inferencing<\/strong><\/em>, we might consider using it to implement an application such as a Medical Diagnosis<\/strong><\/em> system that has an Expert System<\/strong><\/em> subcomponent.<\/p>\n

Creating the DLL:<\/h3>\n

Getting back to our main topic, I decided to create a DLL<\/strong><\/em> in Visual Prolog. <\/strong><\/em>The DLL<\/strong><\/em>\u00a0provides the following:<\/p>\n

1) A function<\/strong><\/em> called “factorial”<\/strong><\/em> that takes an integer argument and returns the corresponding factorial of the argument.<\/p>\n

2) A procedure<\/strong><\/em> called “lookup”<\/strong><\/em> that takes two arguments: an integer, which acts as a “key”<\/strong><\/em> for lookup and and an “out”<\/strong><\/em> parameter that corresponds to the looked up value.\u00a0 <\/span>In case the integer “key”<\/strong><\/em> is not present, it will assign “-999999”<\/strong><\/em> to the output argument.<\/p>\n

As you can see, Visual Prolog<\/strong><\/em> supports functions and procedures too, in addition to the regular non-deterministic\u00a0“Horn Clauses”<\/strong><\/em>\u00a0.\u00a0<\/span><\/p>\n

Since Visual Prolog is “object oriented”<\/strong><\/em>, functionality is implemented in classes, whose code is distributed in three files:<\/p>\n

– “Interface”<\/strong><\/em> file, which defines the interface\/behaviour provided by the “objects”<\/strong><\/em> of a class<\/p>\n

– “Class”<\/strong><\/em> file, that declares the class-specific interface<\/p>\n

– “Implementation”<\/strong><\/em> file that implements the clauses, etc. declared in the above\u00a0two files<\/span><\/p>\n

In some cases, the “interface”<\/strong><\/em> is not required (if we are not going to create class instances), but the other two are must.<\/p>\n

I created a “New Project”<\/strong><\/em> with the type as “DLL”<\/strong><\/em>:<\/p>\n

\"Visual<\/a>
Visual Prolog Project<\/strong><\/em><\/figcaption><\/figure>\n

When I click “Finish”, the IDE generates the necessary files in the selected directory.<\/p>\n

Here are the two predicates that I export from the DLL<\/strong><\/em> (they are declared in the “class”<\/strong><\/em> file):<\/p>\n

\"The<\/a>
The Class File<\/strong><\/figcaption><\/figure>\n

Here is the corresponding implementation:<\/p>\n

\"The<\/a>
The Implementation File<\/strong><\/figcaption><\/figure>\n

When I create the DLL<\/strong><\/em> project, the IDE automatically generates the “main”<\/strong><\/em> module that takes care of creating and initializing the DLL<\/strong><\/em>. Here is the generated code:<\/p>\n

\"DLL<\/a>
DLL Initilization<\/strong><\/figcaption><\/figure>\n

The “Build”<\/strong><\/em> command (Control + Shift + B) causes the IDE to compile the project and emit the DLL<\/strong><\/em> as well as the LIB<\/strong><\/em> file. The DLL<\/strong><\/em> is saved in the “exe64”<\/strong><\/em> subdirectory and the LIB file in the “Lib64”<\/strong><\/em> directory inside the Project directory “DllTest”<\/strong><\/em>.<\/p>\n

Using the DLL from a C++ Program:<\/h3>\n

I decided to load the DLL<\/strong><\/em> dynamically in my C++<\/strong><\/em> program, so there was no need for the LIB<\/strong><\/em> file. I wrote a simple wrapper<\/strong><\/em> to interface with the Visual Prolog<\/strong><\/em> code:<\/p>\n

\"The<\/a>
The Wrapper Class<\/strong><\/figcaption><\/figure>\n

Take a look at line 40<\/strong><\/em>. Since the Prolog “lookup”<\/strong><\/em> procedure retuns the result via “out”<\/strong><\/em> parameter, I need to pass the address<\/strong><\/em> of the “result”<\/strong><\/em> variable. Visual Prolog<\/strong><\/em> will store the looked up value in this address.<\/p>\n

And here is the “main”<\/strong> <\/em>function:<\/p>\n

\"C++<\/a>
C++ Main Entry Point<\/strong><\/em><\/figcaption><\/figure>\n

First, I have to create an instance of the “wrapper”<\/strong><\/em> class, initializing it with the correct path<\/strong><\/em> of the DLL<\/strong><\/em> to be used. The prolog calls are then routed through this object. Nothing fancy here.<\/p>\n

I used Embarcadero’s RAD Studio<\/a> ver 10.4.2<\/strong><\/em> to build the C++<\/strong><\/em> application (64-bits).<\/p>\n

Here is the output from the program:<\/p>\n

\"Program<\/a>
Program Output<\/strong><\/figcaption><\/figure>\n

The program works as expected. When time permits, I intend to check out the other interesting features that Visual Prolog<\/strong> <\/em>has to offer.\u00a0<\/span><\/p>\n

You can download the Visual Prolog\u00a0<\/strong><\/em>project here<\/strong><\/em><\/a>. The C++ <\/strong><\/em>source file is here<\/strong><\/em><\/a>.<\/p>\n

Have a nice weekend!<\/p>\n","protected":false},"excerpt":{"rendered":"

Visual Prolog\u00a0has its roots in Turbo Prolog, which was popularized by Borland in the mid 1980s. It is developed and supported by PDC A\/S, Denmark. So how is Visual Prolog different from other Prolog implementations out there, for example, SWI-Prolog or Sicstus Prolog? Here are the key differences: 1) It is not an ISO Prolog\u00a0 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[49,17,147],"tags":[149,283],"class_list":["post-2433","post","type-post","status-publish","format-standard","hentry","category-c","category-programming","category-prolog","tag-dll","tag-visual-prolog"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9OLnF-Df","jetpack-related-posts":[{"id":1770,"url":"https:\/\/www.rangakrish.com\/index.php\/2019\/11\/10\/calling-c-methods-from-sicstus-prolog-through-com-interface\/","url_meta":{"origin":2433,"position":0},"title":"Calling C# Methods from Sicstus Prolog through COM Interface","author":"admin","date":"November 10, 2019","format":false,"excerpt":"Recently\u00a0I needed to make use of a C# library (which I had implemented a few years ago) from Sicstus Prolog. Calling C\/C++ functions from Sicstus Prolog is fairly well documented. When it comes to C#\/.NET, the official documentation recommends the PrologBeans library. 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In order to\u2026","rel":"","context":"In "Natural Language Processing"","block_context":{"text":"Natural Language Processing","link":"https:\/\/www.rangakrish.com\/index.php\/category\/natural-language-processing\/"},"img":{"alt_text":"Creating WordNet Prolog Image","src":"https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2018\/08\/Creating-image.png?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2018\/08\/Creating-image.png?resize=350%2C200 1x, https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2018\/08\/Creating-image.png?resize=525%2C300 1.5x"},"classes":[]},{"id":1004,"url":"https:\/\/www.rangakrish.com\/index.php\/2018\/08\/05\/sicstus-prolog-building-a-windows-dll\/","url_meta":{"origin":2433,"position":2},"title":"Sicstus Prolog – Building a Windows DLL","author":"admin","date":"August 5, 2018","format":false,"excerpt":"Last week I upgraded to the latest version (4.4.1) of Sicstus Prolog\u00a0for Windows.\u00a0Since the Prolog engine can be embedded (royalty free) in other applications, it is useful to understand how to create a DLL (on Windows) for this purpose. In today's article, I would like to outline this process in\u2026","rel":"","context":"In "C++"","block_context":{"text":"C++","link":"https:\/\/www.rangakrish.com\/index.php\/category\/c\/"},"img":{"alt_text":"Creating Prolog Program Image","src":"https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2018\/08\/Saving-Prolog-Image.png?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2018\/08\/Saving-Prolog-Image.png?resize=350%2C200 1x, https:\/\/i0.wp.com\/www.rangakrish.com\/wp-content\/uploads\/2018\/08\/Saving-Prolog-Image.png?resize=525%2C300 1.5x"},"classes":[]},{"id":3555,"url":"https:\/\/www.rangakrish.com\/index.php\/2024\/11\/22\/multiobjective-optimization-moo-in-lisp-and-prolog\/","url_meta":{"origin":2433,"position":3},"title":"Multiobjective Optimization (MOO) in Lisp and Prolog","author":"admin","date":"November 22, 2024","format":false,"excerpt":"Recently I came across a nice article\u00a0by Jose Crespo, where the author stresses that the future of programming revolves around the application of math concepts such as Functor, Monads, Folds, etc. In addition, he argues that familiarity with C\/C++ is essential in this modern AI age. 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