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Prolog: Making a procedure to print Hello World

I want to load this simple something into my Editor:

Write:-repeat,write("hi"),nl,fail.

So that it prints "hi".

What should I do?

I'm currently trying to do File->New

and Saving a file named Write into E:\Program Files\pl\xpce\prolog\lib

When doing the query:

?-Write.

It's printing:

1 ?- Write.
% ... 1,000,000 ............ 10,000,000 years later
% 
%       >> 42 << (last release gives the question)

Why?

Solution

  • EDIT

    I did some more research. Apparently this is what SWI-Prolog does when you ask it about an uninstantiated variable.

    $ prolog
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 5.6.64)
Copyright (c) 1990-2008 University of Amsterdam.
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- X.
% ... 1,000,000 ............ 10,000,000 years later
% 
%       >> 42 << (last release gives the question)
?-

    UPDATE

    Changing the name to lowercase works. Uppercase is for variables:

    helloworld.prolog:

    helloworld:-write('Hello World!'),nl,fail.

    Then:

    $ prolog
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 5.6.64)
Copyright (c) 1990-2008 University of Amsterdam.
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- ['helloworld.prolog'].
% helloworld.prolog compiled 0.00 sec, 1,376 bytes
true.

?- helloworld.
Hello World!
false.

?-

    Notice that you have to consult the file first. I tried this out and it works for sure.