> For the complete documentation index, see [llms.txt](https://cleberjamaral.gitbook.io/mind/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cleberjamaral.gitbook.io/mind/knowledge/programming/prolog.md).

# prolog

Here I have some notes about prolog. I am using [GNU Prolog](http://www.gprolog.org/). More information can be found at [GNU Prolog manual](http://www.gprolog.org/manual/gprolog.html) and [GNU Prolog tutorial](http://mgencer.com/files/PrologTutorial.html).

### First steps

Prolog is a symbolic language in which we declare facts and rules to then ask questions that will be answered based on these data. 

### Installing gnu prolog

Download and uncompress [gprolog-1.4.5](http://www.gprolog.org/). After going to gprolog folder:

`$ ./configure`\
`$ make`\
`$ sudo make install`

### Running a simple application on gnu prolog

Starting in a very simple way, let us prepare a set of facts. In gnu prolog, it must be written in a file. Let us considerer the file **zoo.pl** with the following content:

`animal(turtle).` \
`animal(tiger).` \
`animal(giraffe).`

Running gnu prolog on the folder we have the file zoo.pl:

`$ gprolog`\
`GNU Prolog 1.4.5 (64 bits) Compiled Apr 12 2020, 18:50:29 with gcc` \
`By Daniel Diaz` \
`Copyright (C) 1999-2020 Daniel Diaz`\
`|?-` 

Importing **zoo.pl** and making first assertion:

`|?- consult(zoo).`\
`|?- animal(X).`

The answer will be `X = turtle ?`, pressing `;` it shows `X = tiger ?`, pressing `;` again it shows the last true value for X: `X = giraffe`. The command `consult(file)` and be replaced by `[file]`.

In fact, currently, it is all we have in the database as we can check using listing command:

`|?- listing.`\
\
`% file: /media/data/zoo.pl`\
\
`animal(turtle).` \
`animal(tiger).` \
`animal(giraffe).`\
\
`yes`\
`|?-`

To exit from gnu prolog:

`|?-` Ctrl+C, then `e` (to exit).

### Adding new facts

`|?- assertz(bigger(giraffe,lion)).`\
`|?- assertz(bigger(lion,turtle)).`

### Appending elements to a list

```
append_element([],E,[E]). 
append_element([H|T],E,[H|L]) :- append_element(T,E,L).
```

### To be continued...

I am following the material from <http://www.cs.trincoll.edu/~ram/cpsc352/notes/> which is very practical.