I'm trying to write a prolog server to be able query a knowledge base written in prolog from a client written in another programing language (Python, JavaScript, whatever...) much as one can an SQL database.
I would have thought this was quite a common thing to do, but I can't find any examples on the web.
All the required socket functions seem to be listed at https://www.dcc.fc.up.pt/~vsc/Yap/documentation.html#Sockets and the reason I'm using yap rather than swi-prolog is I want to use a Unix socket, not a TCP/IP socket. But I'll use AF_INET here since AF_UNIX isn't supported by swi-prolog.
Writing a server that writes a string from the client is easy:
#!/usr/bin/yap -L --
:- initialization(main).
main :-
socket('AF_INET', Socket),
socket_bind(Socket, 'AF_INET'('localhost', 1234)),
socket_listen(Socket, 2),
socket_accept(Socket, _Client, Stream),
read(Stream, Term),
write(Term),
socket_close(Socket).
And the simple Python 3 client I'm using looks like this:
import socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect(('localhost', 1234))
sock.send(b"'Hello World\n'")
sock.close()
Where it gets tricky is getting the server to echo the string back to the client, which requires socket_select/5 as far as I understand. But I've no idea from the available documentation how to use it.
