User Input , How can we do it?

Question

How can we get something from user in prolog : for example :

animal(dog).
animal(cat).
write('please type animal name:'),nl.
/* How to read from user and store it to X 
and then check that user has typed animal name ?*/
?-animal(X).

Answer 1

You can use read for that. For example you could write read(X), animal(X). into the prolog interpreter or write this into a script file:

:- read(X), animal(X).

If you then enter a valid animal name into the prompt, it will be bound to X. If you enter an invalid name, it won't.

Or you could define a procedure like this:

read_animal(X) :-
  write('please type animal name:'),
  nl,
  read(X),
  animal(X).

And then call it in the in the interpreter like read_animal(X)..

Note that the input needs to be terminated by a ..