Hello World (Prolog)

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Prolog is a logic programming language that deduces new facts from a knowledge base consisting of facts and rules. The following rule prints a "Hello World!" message:

<<hello_world.pl>>=
hello_world :- write('Hello World!').

write/1 is a built-in predicate which writes a Prolog term to the standard output stream and always succeeds.

Now start the Prolog interpreter which will prompt you to enter a query. Type the following to load the source file:

?- consult(hello_world).
% hello compiled 0.00 sec, 612 bytes
Yes

consult/1 is another built-in predicate that will load the given file as a Prolog program.

Now make the following query:

?- hello_world.
Hello World!
Yes

The "Yes" is the response to your query and indicates that Prolog could deduce hello_world. This is because write always succeeds.

You could just as well have queried directly in the interpreter without writing a rule:

?- write('Hello World!').
Hello World!
Yes

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