How to start the REPL?

How does one envoke the top-level read-eval-print loop?

Context: I want a stand-alone program that does the equivalent of:

swipl -g my_main -- --port=9999 

but using initialization/2, so that I can compile it and start it:

my_program.qlf --port=9999

(I don’t want to run it as a daemon, at least not right now.)

I get part of what you want but can’t connect all of the dots to understand exactly what you want.

Have you looked at boot/ to see if what you desire already exist as a predicate? I know it is in the ball park. :thinking:

I don’t know why I missed it the first time: the answer is prolog (see the comments for '$runtoplevel in boot/

My code now is:

:- initialization(my_program_main, main).
my_program_main :-
    http_server([port(...)]), % starts http server in separate threads
    prolog.  % top level REPL

If I don’t have the call to prolog, the program halts. (If I don’t want the REPL, I suppose I could use thread_httpd:http_current_worker/2 or thread_httpd:current_server/5 and do a thread_join.)

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Alternatively, make the entry point call

set_prolog_flag(toplevel_goal, prolog)

See library(http/http_unix_daemon), enable_development_system/0. If you want a web server on Unix, I’d use this as a basis. Besides all the stuff dealing with Unix daemon processes in several scenarios (start as root to use an privileged port, (not) fork, relay messages to syslog, etc) it also does a lot of work in controlling interaction, setting up the server including HTTPS, etc. For a simple interactive session use e.g.

myapp --port=3000 --interactive