Question

?-dynamic(setup/5).
setup :-
    seeing(S),
    see('people.txt'),
    read_data,
    write('data read'),
    nl,
    seen,
    see(S).
read_data :-
    read(A),
    process(A).
process(A) :- A == end_of_file.
process(A) :-
    A \== end_of_file,
    write('1'),
    read(B),
    read(C),
    read(D),
    read(E),
    assertz(person(A,B,C,D,E)),
    read_data.

and the text are

john.will.30.london.doctor.
martha.will.33.portsea.doctor.
henry.smith.26.manchester.doctor.

the result is coming out

?- setup.

* Syntax Error

* Syntax Error

* Syntax Error

* Syntax Error

* Syntax Error
data read
yes

What happens? What did I do wrong?

Answer 1

You are reading with read/1 which expects valid Prolog text as input. However, your data is

john.will.30.london.doctor.

which is invalid. Write something like

person(john,will,30,london,doctor).

instead. Most often, people do not read in such data manually. Instead, they load the file with ['datafile.pl'] or other commands.